Final Report on: The Rolling Grant on High Temperature Superconductors from Fundamentals to Applications

EPSRC GR/J85523 01/06/94 to 31/05/98

Principal Investigator

Professor Colin Gough
Director of Superconductivity Research, University of Birmingham Professor of Condensed Matter Physics

Co-applicants

Physics
Professor Joe Vinen FRS, Professor Ted Forgan, Dr Chris Muirhead, Dr Alastair Rae

Chemistry
Professor Peter Edwards, Professor Colin Greaves, Dr Ian Gameson

Materials Science
Professor Stuart Abell, Professor Rex Harris

Electrical Engineering
Dr Mike Lancaster, Dr Fred Huang

Contents:

  • Background
  • Summary of Birmingham Highlights
  • Sub-sections:
     

  • Pulsed Laser Deposition Facility
  • Microstructural Characterisation
  • Physical Characterisation and Enabling Science
  • Flux Lattice Studies
  • Device Physics
  • Textured Film Materials
  • Novel Superconductors
  • Synthesis Of Improved Performance Superconductors
  • Microwave Properties, Device and Antenna Applications


  • Background

    The multidisciplinary Birmingham Superconductivity Group was formed very soon after the discovery of high temperature superconductors in 1987 and was based on pre-existing research collaborations on conventional superconductors involving Physics, Chemistry, Metallurgy and Materials Science and Electronic and Electrical Engineering. Although the IRC in Superconductivity was awarded to Cambridge University, the SERC and subsequently EPSRC have continued to support a strong interdisciplinary programme at Birmingham, which has been largely complementary to that at Cambridge, through a continuing sequence of Rolling Grants of which this was the last to be awarded under the old arrangement.

    Such grants, including the present one, have been regularly reviewed on a two-yearly cycle, on which the decision for a further 4-year?s funding was dependent. Each two-year review involved the preparation of a new 4-year research proposal , a panel visit of "experts" and the normal peer review assessment. Now that the overlapping renewable rolling grant has disappeared from favour, the Birmingham programme was reviewed just over a year ago, for a continued 3-year programme, under the normal responsive mode grant arrangements within Functional Materials, though a panel visit was also arranged because of the size of the application. This Final Report reproduces much of the material considered by the EPSRC in supporting the Birmingham Superconductivity Programme for a further three year?s funding from June 1st 1998 to 2001.

    For convenience we will describe achievements under the following headings, which closely mirror the programmes funded under the Rolling Grant from 1994-1998 and the continued programme under the recently awarded grant. A summary of some of major advances in the period 1994-1998 provides a quick overview of the Birmingham programme. Each of the programmes below typically involved 1 PDRA and some technical support.

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    Summary of Birmingham Highlights (1994 - 1998)

    The Superconductivity Group has published over 200 refereed journal and conference papers since 1994. Lists of publications for each of the component programmes are attached to the end of case for support for each of the sub- programmes attached as Appendices to the end this section. The majority of the applicants have given a significant number of invited talks at major international conferences and have served on the Organising and Programme Committees of almost every major international conferences on HTS. We list below a number of highlights from the Rolling Grant and from closely related research and collaborations. A significant number of the highlighted topics are world-firsts. Not all these highlights, particularly on the more applied side, were directly funded from the Rolling Grant programme, but none of them would have been possible without the infra-structure of equipment, facilities and local expertise that has been made possible by the continued sequence of Rolling Grants over the last ten years.

    1. Paramagnetic Meissner Effect in 2212-BSCCO, disproving a p-junction explanation - PRB 53, 12441 (1996)
    2. Flux lattice/melting/nucleation in YBCO thin film microbridges (with DRA Malvern) -EUCAS 95, IOP, pp 1343
    3. First observation/modelling of flux diffusion in YBCO/PBCO superlattice films -Solid State Comm. 101, 51(1997)
    4. Universality of flux noise and observation of creep at individual flux quantum level -PRB 55, April (1997)
    5. Determination of intrinsic noise of a GHz rf-SQUID -EUCAS 95, IOP, pp 1629
    6. First observation of diffusive flux motion in HTS superlattices -Solid State Comm.101, 51 (1997)
    7. Field dependence of c-axis conductivity in 2212-BSSCO single crystals - PRB 51, 6655 (1995)
    8. Growth, structural and physical characterisation of YBCO/PrBCO superlattice structures (EC Network on HTS Multilayers and Superlattices) - IEEE Trans on Appl. Sup. 5, 1646 (1995)
    9. The irreversibility line, flux dynamics and low field re-entrant phase for 2d flux lines - PRL 75, 1835 (1995)
    10. Flux lattice melting and 3d-2d vortex pinning transformation in BSCCO using mSR and neutron diffraction (this and below involves collaboration with Warwick and St Andrews) -IWCC7 Alpbach, invited talk.
    11. Direct evidence for flux lattice melting in YBCO by neutron diffraction - LT21 invited talk
    12. First investigation of thermal fluctuations of vortices in HTS by mSR -PRL 75, 922 (1995).
    13. mSR measurements of l(T,B) in YBCO and related structures (with Zurich)- PRB 52, 541 (1995)
    14. Theory of magnetisation jumps at flux lattice melting (collaboration with Farrell) - PRB 53, 11807 (1996)
    15. Ambient pressure, bulk synthesis of 1223 Hg-cuprate HTS with Tc ~ 135K- Advanced Materials, 11, 925 (1995)
    16. Structure of 1223 Hg-cuprate up to 105 Atmospheres (with RAL and CNRS) - PRB 52, 15551 (1996)
    17. First powder-in-tube processing for Hg-cuprate silver-sheathed wires- Physica C 273, 193 (1997)
    18. Anisotropic penetration depth of Hg-cuprate compounds (with IRC Cambridge) PRB 53, 2999 (1996)
    19. Synthesis, structure and properties of HgBa2CuO4+d - PRB in press (1997)
    20. First oxide-fluoride superconductor; Nature 369 382 (1994)
    21. Highest Tc material with La2CuO4 type structure; Physica C 241 151 (1995)
    22. Oxy-anion substitutions, M2S-HTSC IV, Grenoble (1994) Invited Talk
    23. Band structure (experimental and theoretical) for Sr2CuO2F2+d - Phys Rev B 52, 2390 (1995)
    24. Extended substitutional range of (La,Y),Ba2Cu3O7+d by thin film Chemistry- Physica C 235-240, 701 (1994)
    25. Magnetic identification of 3d-2d vortex transition in BSCCO -Physica C 235-240, 2713 (1994)
    26. Highest Jc in YBCO-Pt doped thick films - Physica C 271, 164 (1996) and patent.
    27. Highest Jc in YBCO thick film on Ag-substrate by dip-pyrolysis- Physica C 235-40, 629 (194) and patent.
    28. Transport and magnetic critical currents in YBCO thick films (with Cambridge IRC)- J.Appl.Phys 76, 1720 (1994)
    29. Development of barrier layer technology for YBCO thick films on technical (i.e. inexpensive) substrates-ASC 96.
    30. Growth spirals on YBCO thin film are not simple screw-dislocations -Phil. Mag, Letts. 70, 47 (1994) and British Association of Crystal Growth- Young Scientist of the Year Award 1995.
    31. Discovery, structure and characterisation of monoclinic 2212-BSCCO phase-Physica C 235-240, 533 (1994)
    32. Low temperature SEM for local s/c properties and correlation with underlying defect structures (DRA-Malvern and others) - Appl. Phys. Letts. 64, 920 (1994)- and potential commercialisation by Oxford Instruments.
    33. Novel coplanar technique to extract absolute values of l(T,B) - IEEE-MTT 43, 306 (1995)
    34. Temperature and field dependence of l(T,B) and m-wave losses in YBCO/GBCO thin films - LT21, pp 1087 (1996)
    35. Microwave properties of B-dependence high anisotropy of HTS crystals -PRB 50, 448 (1994)
    36. Wide range of HTS microwave filter structures developed including a novel delay line architecture, slow-wave delay lines, switchable filter banks, novel dielectric resonator geometries -IEEE-MTT 44, 1339 (1996)
    37. Demonstration of the world's first HTS superdirectional antenna array in both wire and a 16 element planar thick film circuit.
    38. Coplanar resonator system for ultrasensitive ESR for small samples -EUCAS 95, pp 1215 and patent.
    39. Novel, hollow, dielectric resonator for high sensitivity HTS m-wave measurements - ASC 96 & M2S-HTS 97
    40. Optimisation of thick film properties for microwave applications (patent)
    41. lowest reported surface resistance for thick film material in large area planar and three dimensional structures- IEE Trans. Microwave Techniques 44, 1356 (1996).
    42. Commercial application of microwave thick film resonators for cellular telephone base stations in USA (currently 6 sites) using Birmingham material and technology (Illinois Superconductors).
    43. World record, 13.2 kA current lead (EURUS) using HTS ceramic wires from Birmingham - for Large Hadron Collider experiment at CERN (two leads each required for ~ 800 superconducting magnets).
    44. Novel toroidal Fault Current Limiter designed and demonstrated - for aerospace and power applications - using Birmingham HTS thick films (new project with Elec. Eng and industry - results presented at ASC 96) .
    45. Design and implementation of state of art, microwave filter for the major European consortium developing HTS front-end receivers for mobile communications systems (presented at all major international applied superconductivity conferences in 1998).
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    We are grateful to the EPSRC for their strong support in funding the Birmingham superconductivity core research programme since its formation in 1987 and for the last four years of this Rolling Grant in particular.

    Final reports for each sub-section of the Rolling Grant from 1994 -1998 follow as appendices:
     

    Pulsed Laser Deposition Facility
    Interdisciplinary Facility
    Prof C E Gough, Dr C M Muirhead, Prof J S Abell and Dr M J Lancaster
     

    The Pulsed Laser Deposition Facility (PLDF) was first set_up in 1992 with central funds from the University of Birmingham as the result of an initiative by Prof. C.E. Gough on behalf of the Superconductivity Research Group. EPSRC-support has been received since June 1994 for staffing and operating the Facility, which is housed in the School of Electrical & Electronic Engineering. Since then, much of the HTS-research in the Schools of Physics, Chemistry, Metallurgy and Materials, and Electrical Engineering has been crucially dependent on the provision of high-quality epitaxial thin films from the Facility.

    Scientific guidance for the activities in the PLDF has been provided by Prof. C.E. Gough and the HTS-Management Committee; responsibility for solving project-related technical problems rests with a small team of active researchers, one from each School, working closely with the two PDRA?s in the Facility, Dr. F. Wellhöfer, and Dr. P. Woodall funded partly by the EPSRC funding for a technician, but upgraded to a PDRA using additional contributions from the school of Electronic and Electrical Engineering.

    Since April ?94, some 800 films have been grown by pulsed laser deposition (PLD), and provided the basis for wide-ranging investigations on various aspects of fundamental and applied science in the four different Schools. To date, the PLDF has concentrated its efforts on optimising the growth of single sided YBCO films on MgO- and STO-single crystal substrates. Prior to being distributed to the various Schools, the thin films were initially routinely characterised in the PLDF, i.e. the surface of the films assessed using polarised light, AFM and STM, Jcmag tested at 77K, and Tc determined from ac-susceptibility data. The atomic-force, scanning tunnelling and optical microscopes with polarised light were bought with EPSRC-funds specifically for the PLDF.

    The Facility has served as a central laboratory for researchers from all over campus and has also attracted a large number of external visitors, who have often sought and received detailed technical advice. It has been used to enable visiting European Research Fellows to familiarise themselves with pulsed-laser deposition technology for multi-layered structures, and the use of AFM/STM techniques for assessing variations in the surface-quality of thin films as a function of changing deposition parameters. Invited talks have been given by the two PDRA?s in the PLDF at several workshops aimed at PLD-process development and HTS-thin film quality assurance, and at local FE Colleges. Good external relationships have also been secured by the provision of occasional thin film samples to external visitors free of charge, some of which subsequently developed into fruitful international collaborations as evidenced elsewhere in this application.
     
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    Publications 1994 to 1998

    1. Synthesis and characterisation of laser ablated Yba2-xSrxCu3O7 thin films. Greaves, Slater, Jones, Asab, Shaffery, Gameson, Edwards, Sutton, Wellhofer, Woodall; Physica C, Superconductivity, 235 (1) 701-702
    2. Investigation of the influence of Al-doping on the microstructures of laser ablated epitaxial YBCO thin films on (100) MgO. Yeadon, Hirst, Locherer, Crosch, Abell, Aindow, Wellhöfer, Woodall, Salje. Inst. Phys. Conf. Ser. No 147 p 421-424; EMAG ?95
    3. Development of the surface morphology of laser ablated epitaxial thin films of YBCO on MgO Yeadon, Aindow, Wellhöfer, Woodall, Abell;. Inst. Phys. Conf. Ser. No 147 p 263-266; EMAG ?95
    4. Properties of laser ablated epitaxial thin and ultrathin YBCO-films Yeadon, Aindow, Abell, Slaski, Gough, Woodall, Wellhöfer; Inst. Phys. Conf. Ser. No 148 p 991-994; EUCAS ?95
    5. Experimental study of flux noise in YBCO/PBCO superlattices. Kiss, Klein, Smithyman, Muirhead, Wellhöfer, Woodall; Inst. Phys. Conf. Ser. No 148 p 1027-1030; EUCAS ?95
    6. The effect of selected parameters on the growth of MgO buffer layers by pulsed laser deposition. Sharp, Woodall, Wellhöfer, Sutton, Abell & Earwaker; Inst. Phys. Conf. Ser. No 148 p 875-878; EUCAS ?95
    7. The effect of variations in laser fluence and pulse repetition rate on YBCO thin films. Norris, Aindow, Earwaker, Woodall, Wellhöfer; Inst. Phys. Conf. Ser. No 148 p 879-882; EUCAS ?95
    8. New high temperature superconductive microstrip lines and resonators. Hong, Lancaster, Porch, Avenhaus, Woodall, Wellhöfer; Inst. Phys. Conf. Ser. No 148 p 1195-1198; EUCAS ?95
    9. Microwave surface resistance of unpatterned and patterned YBCO thin films produced by PLD. Porch, Avenhaus, Wellhöfer, Woodall Inst. Phys. Conf. Ser. No 148 p 1039-1042 ; EUCAS ?95
    10. Microwave surface impedance of YBCO thin films in DC applied magnetic fields. Powell, Porch Wellhöfer, Woodall, Gough; Inst. Phys. Conf. Ser. No 148 p1119-1122; EUCAS ?95
    11. Switched YBCO lumped element bandstop filter. Avenhaus, Porch, Huang, Lancaster, Woodall, Wellhöfer; Electronic Letters Vol. 31 No.12 (1995)
    12. Microstructure and properties of laser ablated epitaxial YBCO thin films for electronic device applications. Yeadon, Aindow, Wellhöfer, Abell, Avenhaus, Lancaster, Woodall;. IEEE Transactions on Applied Superconductivity, Vol.5, No.2 (1995) 1214-1217
    13. Magnetic noise properties of YBCO/PBCO superlattices. Drouet, Foulds, Klein, Muirhead, Smithyman, Wellhöfer, Woodall; IEEE Transactions on Applied Superconductivity, Vol.5, No.2 (1995) 1646-1648
    14. Critical currents of laser-ablated epitaxial thin and ultrathin YBCO films. Slaski, Woodall, Wellhofer, Yeadon, Gough; Proc. 8th International Workshop on Critical Currents in Superconductors - Kitakyushu Japan (1996) 423-426, World Scientific.
    15. Microwave surface impedance of YBCO. Powell, Porch, Wellhofer, Humphreys, Gough; Czechoslovak Journal of Physics, 46 (s2) 1089-1090
    16. Induction of superconductivity in pulsed laser ablated La2CuO4 thin films by post deposition fluorination Lees, Gameson, Jones, Edwards, Greaves, Wellhofer, Woodall, Langford & Slaski; "Physica C", Superconductivity, 270 (3-4) 305-310 (1996)
    17. Frequency dependence of the ac-sheet conductivity in thin YBCO-films. Björnander, Magnusson, Svedlinh, Nordblad, Norton, Wellhöfer; Physica C, Superconductivity, 272 (3-4) 326-334 (1996)
    18. Laser ablated ferroelectric and superconducting thin films for microwave applications, Powell J. R., Porch A., Wellhofer F., Darlington C. N., Lancaster M. J., Bollmeier T., and Stritzker B, IEE Colloquium on the Microwave Applications of Superconductors April 19th 1996
    19. The effect of selected process parameters on laser ablated YBCO thin films on SrTiO3 substrates. F. Wellhofer, P. Woodall, D.J. Norris, M. Aindow, M. Slaski, L.G. Earwaker. Journal Of Alloys And Compounds, Vol.251, No.1-2, pp.123- 128 (1997)
    20. Mapping the variations in properties of PLD films of YBCO deposited over large areas. P. Woodall, F. Wellhofer, D.J. Norris, M. Aindow, L.G. Earwaker. Journal Of Alloys And Compounds, Vol.251, No.1-2, pp.172- 175 (1997)
    21. Induction of high-temperature superconductivity in pulsed laser ablated La2CuO4 thin films by room temperature chemical oxidation. Lees, Edwards, Gameson, Jones, Slaski, Rial, Amador, Moran. "Advanced Materials" (1997), Vol.9, No.10, p.823
    22. The effects of Al substitution on the microstructure and properties of laser-ablated epitaxial YBCO films on (001) MgO, M. Yeadon, P. Hirst, K. Locherer, J. Chrosch, J.S. Abell, M. Aindow, F. Wellhofer and E. Salje, Physica C 274 (1997)
    23. Topographical development and misfit relief in laser-ablated heteroepitaxial YBCO thin films, M. Yeadon, M. Aindow, F. Wellhofer and J.S. Abell, Journal Of Crystal Growth, Vol.172, No.1-2, pp.145-155 (1997)
    24. STM surface modification of YBa2Cu3O7-d thin films. S.E. Johnson, M. Yeadon, M. Aindow, P. Woodall, F. Wellhofer, J.S. Abell. Institute Of Physics Conference Series, No.153, pp.437-440 (1997)
    25. Magnetic noise in YBCO thin films and its relationship to growth morphology. J. Smithyman, C. Muirhead, M. Aindow, F. Wellhofer, P. Woodall. IEEE Transactions On Applied Superconductivity, Vol.7, No.2 Pt2, pp.1624-1627 (1997)
    26. The effect of substrate vicinal offcut on the morphology and defect microstructure of YBa2Cu3O7-x thin films on (001)SrTiO3. D. Vassiloyannis, D.J. Norris, S.E. Johnson, M. Aindow, P. Woodall, F. Wellhofer. Institute Of Physics Conference Series, No.153, pp.449-452 (1997)
    27. A demonstration of the HTS microwave sub-system with pulse tube cooler, Hong Li, Wenxiou Zhu, Jinghui Cai, Pingsheng Zhang, Yuan Zhou, Aisheng He, Zhonglin Gong, Yusheng He, Smith P., Button T., Alford NMcN., Lancaster M. J., Porch A., Avenhaus B., Woodall P., Wellhofer F., Gough C. E., Kaiser G., Seidel P., and Thurk M. Physica C 282-287 pp 2527-2528 (1997)
    28. Demonstration of HTS microwave sub-systems with a pulse tube cryocooler, H.Li, W.X.Zhu, J.H.Cai, P.S.Zhang, Y.Zhou, A.S.He, Z.L.Gong, T.S.He, P.A.Smith, T.W.Button, J.E.Holmes, M.J.Lancaster, A.Porch, B.Avenhaus, P.Woodall, F.Wellhofer, C.E.Gough, G.Kaiser, P.Seidel, M.Thurk, Physica C, Vol.282, No.Pt4, pp.2527-2528 (1997)
    29. Electron beam induced voltage contrast and modulated optical reflectance studies of YBCO thin, film resonators, S.A.L. Foulds, D. Almond, P. Nokrach, F. Wellhofer, P. Woodall and J.S. Abell, Sup. Sc. Techn. 11 (1998) 378-382.
    30. Field, temperature, and frequency dependence of the surface impedance of YBa2Cu3O7 thin films, J R Powell, A Porch, R G Humphreys, F Wellhofer, M J Lancaster, C E Gough, Physical Review B-Condensed Matter, Vol.57, No.9, pp.5474- 5484 (1998)
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    MC - Microstructural Characterisation
    Professor Stuart Abell
     

    Microstructural characterisation has always been a central activity for the whole Birmingham Superconductivity programme, developing and underpinning our understanding of the relationship between processing and superconducting properties of a wide range of materials, including thin and thick films, textured bulk samples, single crystals, wires and tapes, and newly synthesised materials. The programme also supports basic research on the morphology and growth mechanisms of crystals and epitaxial thin films, and is responsible for developing novel characterisation techniques for correlating microstructural and superconducting properties. The support in this area provided by the rolling grant was for 1 PDRA and an experimental officer (EO) post; the primary role of the PDRA during the period of the grant has been to continue development of the LTSEM/EBIV technique for imaging the spatial distribution of critical currents in thin film device structures, while the EO post has been responsible for providing the inter-disciplinary materials characterisation.

    The establishment of the EBIV technique has allowed the electrical properties of a wide variety of device configurations to be studied in collaboration with a number of thin film groups, eg. Conductus, DRA, IRC. Several technical developments in the LTSEM system have allowed significant improvements in signal to noise and data acquisition to be achieved. These include beam blanking to provide well-defined electron pulses, reducing image noise, a temperature sensor at the sample to provide more accurate temperature measurement, a heat sunk amplifier chip to yield an order of magnitude reduction in signal to noise, a sample field coil to provide small fields ~1mT, software development and new in-column electronics to allow I/V curves to be obtained, modified radiation shields to reduce base sample temperature. The performance of a DRA flux transformer has been studied under various bias conditions leading to a major redesign of the crossover steps[1,2]. Recent studies have centred on c-axis microbridges from DRA. The effect of film thickness and step height on current carrying capacity of microbridges traversing steps in a substrate has been studied in collaboration with IRC Cambridge[3]. Software development has allowed 2D high, low and band pass filtering to be applied to images [4]. A collaboration with Oxford Instruments is considering the commercial exploitation of this technique, and that of secondary electron voltage contrast, in order that the company can offer an additional property mapping technique to their range of SEM facilities. In particular, correlations between voltage contrast imaging and high spatial resolution microstructural back scattered electron diffraction images will be of considerable significance for device characterisation.

    Current microstructural research ranges from investigating the growth mechanisms of epitaxial YBCO films on different substrates and characterising the resultant microstructure, to studying the defect microstructure of device configurations such as step edge junctions. Correlations between voltage contrast observations and detailed microstructure are now being established. Microstructure and surface morphology are being studied using scanned probe microscopy (SPM) scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Problems associated with substrate surface quality can be minimised by the deposition of homo-epitaxial layers (MgO on MgO). MgO barrier layers can be utilised to take advantage of technical substrates, such as sapphire and silicon, while avoiding problems of interdiffusion. The development of the microstructure and surface morphology of PLD films has been studied by SPM and TEM. The high density of spiral growth features at the film surface correspond to threading dislocations observed by TEM. Correlations with critical current measurements indicate that the dislocations act as strong secondary pinning sites for magnetic flux [5]. Careful analysis of the nature of the dislocations shows them to be mixed in character introduced as half loops, and not screw dislocations formed by the coalescence of incoherent growth fronts as previously reported [6]. The topographical development and misfit relief have been studied on MgO and STO and the critical thickness at which spirals are observed are consistent with emergent threading half loop segments introduced in response to the residual misfit [7]. The misfit dislocations at the film substrate interface have been identified by HREM and the nature of the interface established as semi-coherent rather than grapho-epitaxial as proposed previously [8]. Recent work in collaboration with Cambridge University (Prof. E. Salje) has studied the effect of Al substitution on the twin microstructure of laser ablated thin films by means of HRXRD, allowing mismatch strain and mosaicity to be characterised[9]. Corresponding SPM and TEM observations reveal that the spiral density increases dramatically with Al and at a critical concentration a twin to tweed transition occurs associated with the film exhibiting macroscopic tetragonality [10]. The effect of variations in selected deposition parameters on the microstructure and crystallinity of the films has been investigated by RBS, ion beam channelling and HREM [11]. The crystallinity at the film surface is better than at the interface and HREM showed the corresponding presence of misfit dislocations at the interface [8]. The line profiles of patterned YBCO tracks as a function of film thickness and ion milling angles has been studied by SEM and the quality of subsequent growth over these steps has been investigated by TEM in a collaboration with DRA.

    Detailed TEM observations of dislocation networks in BSCCO crystals have been particularly successful in establishing a direct correspondence between the control of defect structures by heat treatment and the associated changes in flux pinning behaviour determining the critical currents and magnetic properties. [12]. These studies also led to the discovery of an orthorhombic to monoclinic transformation with associated twinning [13]. TEM has also been instrumental in analysing the role of flux pinning additions in thick films.

    Microstructural characterisation is playing an increasingly significant role in the fundamental understanding and the technological development of HTS materials. Interfacial structures in BSCCO wires and tapes are critical to the optimisation of the Jc behaviour, dislocation structures in bulk and thick film materials and in single crystals determine the superconducting properties, and control of microstructure at the nanometer to micron scale is going to play an increasingly important role in future materials developments. As thin film technology becomes more sophisticated and device configurations more complex, the need to study growth morphologies and defect microstructures of single and multi-layer films, and to understand the underlying growth mechanisms of both superconducting and insulating layers becomes increasingly important. In particular, the growth of atomically smooth surfaces is vital to multi-layer configurations.

    The correlation between device performance as revealed by LTSEM / EBIV and the prevailing microstructure is of fundamental importance in the optimisation of film properties and determining their dependence on growth parameters. This dependence of critical current distribution and underlying layer configuration and prevailing defect microstructure has been demonstrated by observations on TEM cross section samples of a variety of DRA device structures such as simple bi-layer cross-overs, and more complex multilayer step junctions. The step angles ion beam milled into underlying layers have been shown to have a significant effect on the quality of growth of subsequent layers and the resultant presence of line and planar defects at the steps. The morphology of growth over these steps has been characterised by STM/AFM and correlated with the EBIV performance of these steps under current bias conditions.

    The EBIV technique is now an established facility and can give valuable data on suitable samples. In that sense it can now be regarded as an addition to the wide range of microscopic techniques available in Birmingham. It has, however, become increasingly apparent that the detailed microstructural examination of films, crystals etc. provides an unequalled range of information vital to our understanding of thin film growth processes and the correlation of defect microstructures and superconducting behaviour. A recent development has been the correlation of low temperature voltage contrast and room temperature modulated optical reflectance observations on thin film microwave resonators [60]. This work provides evidence that the normal state MOR signal can be used to infer the spatial distribution of superconducting behaviour on a wide range of materials and is currently the subject of a separate EPSRC proposal.

    The increased use of magneto-optical characterisation to map the spatial distribution of current flow and flux penetration in HTS materials is having a profound effect on our understanding of how precisely these materials behave under operational conditions. Several groups have demonstrated the power of this approach in mapping current flow in BSCCO wires and tapes, and for flux penetration studies on bulk materials and single crystals.(eg. Phys. Rev. B53,1996, 8687, Super. Sci. Techn. 8,1995,199). Little work has been reported on observations on thick and thin films and it is in this area that we have recently been concentrating our efforts. We are in the process of developing our own magneto optic microscope facility including the growth of the required magneto optic thin films by laser ablation. While waiting for our own system to be operational and properly funded under the renewed grant, we are collaborating closely with ISTEC, Larbalestier?s Group in the States and other European Groups correlating superconducting properties of thin films, thick films and single crystals with magneto-optic images of the microscopic flux distributions.

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    Publications (1994-1998)

      1. Spatially Resolved Critical Current Limitations in YBCO Multilayer Structures, C.A. Hollin, S.W. Goodyear, N.G. Chew, R.G. Humphreys and J.S. Abell, App. Phys. Lett., 64 (1994) 918-920.
      2. The Origins of Growth Spirals on Laser-Ablated YBa2Cu3O7-d Thin Films, M. Aindow and M. Yeadon, Phil. Mag. Letts 70: 47-54 (1994).
      3. Correlation of magnetic properties with structural defects in 2212 BSCCO crystals, G. yang, P. Shang, S.D. Sutton, I.P. Jones, J.S. Abell and C.E. Gough, Physica B 194-196 (1994) 1543-1544.
      4. Correlation between Magnetisation and Flux Creep in RBCO (R=Y,Tm),A.A. Zhukov, L.F. Cohen, G. Perkins, A.D. Caplin, S.A. Klestov, V.I. Voronkova, A. Marshall and J.S. Abell, Physica B 194-196 (1994) 1921-1922
      5. Scaling Features in M-H Loops of YBCO Single Crystals, M. Oussena, S. Porter, P.A.J. deGroot, A. Marshall and J.S. Abell, Physica B 194-196 (1994) 1883-1884
      6. Magnetisation Scaling on YBCO Single Crystals, M. Oussena, P.A.J. de Groot, A. Marshall and J.S. Abell. , Phys. Rev. B. 49 (1994) 1484-1487.
      7. A compositional and structural study of the phase Ba(Zr,Cu)O3, A. Marshall, T.C. Shields and J.S. Abell, J. Mater. Sci., 29 (1994) 1930-1934.
      8. Magnetic Identification of 3D to 2D Decomposition transition in BSCCO 2212 Single Crystals, G. Yang, J.S. Abell and C.E. Gough, Proc. IWCC, Alpbach, (1994) 264-267.
      9. A study in flux dynamics of RBCO Single Crystals, L.F. Cohen, A.A. Zhukov, G. Perkins, H.J. Jensen, S.A. Kestlov, V. Voronkova, J.S.Abell, T.Wolf and A.D.Caplin, Proc. IWCC, Alpbach (1994) 217-220.
      10. Magnetic identification of 3D to 2D vortex transitions in BSCCO single crystals, G. Yang, C.E. Gough and J.S. Abell, Physica C 235-240 (1994) 2713-2714.
      11. Synthesis and characterisation of laser ablated YBa2-xSrxCu3O7 thin films, C. Greaves, P.R. Slater, M.O. Jones, A. Asab, P. Shaffery, I. Gameson, P.P. Edwards, S. Sutton, F. Wellhofer and P. Woodall, Physica C 235-240 (1994) 701-702.
      12. Studies by neutron diffraction and µSR of flux lattice orientation, pinning, melting and decomposition in HTC superconductors, E.M. Forgan, R. Cubitt, M.T. Wylie, G. Yang, S.L.Lee, H. Keller, D. McK. Paul, M. Yethiraj, H.A. Mook and P.H. Kes, Proc. IWCC, Austria (1994) 21-26
      13. Monoclinic phase transformation and related (100) twinning in BSCCO single crystals, P. Shang, G.Yang, I.P. Jones, C.E. Gough and J.S. Abell, Ibid. 533-534.
      14. The microstructure of the twin to tweed transition in Al substituted YBCO single crystals, P.J. Hirst, A. Drake, M.Rand and J.S. Abell, Ibid. 371-372.
      15. Spatially resolved electrical characterisation of YBCO/PrBCO multilayer structures, C.A. Hollin, S.W. Goodyear, N.G. Chew, R.G. Humphreys and J.S. Abell, Ibid. 721-722.
      16. Magnetic Relaxation Behaviour of YBCO and BSCCO Crystals, L.F. Cohen, D. Lacey, G. Perkins, A.D. Caplin, J.S. Abell, A.A. Zhukov and V.I. Voronkova, Ibid. 2885-288
      17. Vector Magnetisation studies of interlayer coupling and intrinsic pinning in YBCO, D. Lacey, L.F. Cohen, G.K.Perkins, J.S. Abell and A.D. Caplin, Ibid 2595-2596.
      18. A study of an YBCO flux transformer using LTSEM beam induced voltage contrast, S.A.L. Foulds, Sutton, M.N. Keene and J.S. Abell, Inst.Phys.Conf.Ser. 148 (1995)1581-1584.
      19. Filtering options for low temperature SEM beam induced voltage contrast images, S.A.L. Foulds, K.J.Hulbert, P.Zarucki and J.S.Abell, Inst. Phys. Conf. Ser. 148 (1995)313-316.
      20. Microstructures and Properties of Laser-Ablated Epitaxial YBa2Cu3O7-d Thin Films for Device Applications, M. Yeadon, M. Aindow, F.Wellhöfer, J.S. Abell, B. Avenhaus, M.J. Lancaster and P. Woodall, IEEE Trans. Appl. Supercond. 5: 1214-1217 (1995).
      21. Investigation of the Influence of Al-Doping on the Microstructures of Laser-Ablated Epitaxial YBa2Cu3O7-d Thin Films on (001) MgO, M. Yeadon, P.J. Hirst, K.R. Locherer, J. Chrosch, J.S. Abell, M. Aindow, F. Wellhöfer, P. Woodall and E.K.H. Salje, in "Electron Microscopy and Analysis 1995" editor D. Cherns, Inst. Phys. Conf. Ser. 147:421-424 (1995).
      22. The Effect of Variations in Laser Fluence and Pulse Repetition Rate on YBCO Thin Films, D.J. Norris, M. Aindow, L.G. Earwaker, P. Woodall, and F. Wellhöfer, in "Applied Superconductivity 1995" ed. D. Dew-Hughes, Inst. Phys. Conf. Ser. 148: 879-882 (1995).
      23. Physical and microstructural properties of low resistance contacts to YBCO, C.A. Hollin and J.S. Abell., Superconductor Science and Technology 8 6-14 (1995)
      24. Microstructures and properties of laser-ablated Epitaxial YBCO Thin Films for Electronic Device Applications. M. Yeadon, M. Aindow, F. Wellhofer, J.S. Abell, B. Avenhaus, M.J. Lancaster and P. Woodall, IEEE Trans. Appl. Supercond. 5 (1995) 1214-1217.
      25. The Specific Heat of YBCO Single Crystals, N. Overend, M.A. Howson, S. Abell and J. Hodby, J. of Superconductivity, 8 (1995)
      26. The effect of thickness on the magnetic properties of melt processed YBCO thick films, N.J.C. Ingle, D.A. Cardwell, A.R. Jones, F. Wellhofer and T.W. Button, Supercond. Sci. Technol. 8 (1995) 282-290.
      27. Field and temperature dependence of the c-axis critical current in BSCCO single crystals at the melting and two-dimensional decomposition fields, Sheng Luo, Guang Yang and C.E. Gough, Phys. Rev. B 51 (1995) 6655-
      28. Magnetisation measurements on 2212 BSCCO single crystals - anomalies at the irreversibility temperature., M. Slaski, G. Yang, C.M. Muirhead and C.E. Gough, Ibid. 125-128.
      29. Misfit Dislocations in Heteroepitaxial YBa2Cu3O7-d on (001)MgO, M. Aindow, D.J. Norris and T.T. Cheng, Phil. Mag. Lett. 74: 267-272 (1996).
      30. Doping studies on the orthorhombic to monoclinic phase transformation in BSCCO, G. Yang, P. Shang, I.P. Jones, J.S. Abell and C.E. Gough, Physica C 260 103-110 (1996)
      31. A comparison of critical and lowest-Landau-level scaling of the specific heat of several YBCO single crystals, N. Overend, M.A. Howson, I.D. Lawrie, S. Abell, J.W. Hodby, S.E. Inderhees and M.B. Salamon, Phys.Rev.B 54 9499-9508 (1996)
      32. Growth and Microstructure of BSCCO 2212 crystals, G. Yang, J.S. Abell, P. Shang, I.P. Jones and C.E. Gough, J. Crystal Growth 166 820-824 (1996)
      33. Texture formation in silver-sheathed Bi-based superconducting tapes, J. Jiang and J.S. Abell, Inst. Phys. Conf. Ser. 148 407-410 (1995)
      34. Properties of laser ablated thin and ultra-thin YBCO films, M. Yeadon, M. Aindow, J.S. Abell, M. Slaski, C.E. Gough, P. Woodall and F. Wellhofer, Ibid. 991-994
      35. The effect of selected parameters on the growth of MgO buffer layers by pulsed laser deposition, E. Sharp, S.D. Sutton, J.S. Abell, P. Woodall, F. Wellhofer and L.G. Earwaker, Ibid. 875-878.
      36. Investigation of the influence of Al doping on the microstructure of epitaxial thin films of YBCO on (001) MgO, M. Yeadon, P.J. Hirst, K.R. Locherer, J. Chrosch, J.S. Abell, M. Aindow, F. Wellhofer, P. Woodall and E.K.H. Salje, Ibid. 421-424.
      37. Development of the surface morphology of laser ablated epitaxial thin films of YBCO on MgO, M. Yeadon, M. Aindow, F. Wellhöfer, P. Woodall and J.S. Abell, Ibid. 263-266.
      38. Phase transformation in BSCCO 2212 single crystal, G. Yang, P. Shang, I.P. Jones, J.S. Abell and C.E. Gough, Ibid., 441-444
      39. Electron back scatter diffraction study of melt processed HTC superconductor YBCO, T.C. Shields, A. Drake and J.S. Abell, Ibid. 425-428.
      40. The effects of precursor powder on the texture formation in BSCCO/Ag tapes, J. Jiang and J.S. Abell, Proc. TMS Meeting, Anaheim( 1996) 13-21.
      41. In-situ kinetic neutron diffraction study of melt cast BSCCO rods under an applied dc field, P.S. Whitfield, J. Bhakta, J.S. Abell, Ibid. 197-202
      42. X-ray analysis of mesoscopic twin structures, K.R. Locherer, S.A. Hayward, P.J. Hirst, J. Chrosch, M. Yeadon, J.S. Abell and E.K.H. Salje, Phil. Trans. R. Soc. Lond. A 354 (1996) 2815-2845
      43. Preparation of High Temperature Superconducting Silver-Sheathed HgBaCuO4+x Tapes, G.B. Peacock, M. Khaliq, G. Yang, T.C. Shields, I. Gameson, J.S. Abell and P.P. Edwards, Physica C 272 (1997) 193-197 .
      44. Effects of a geometrical length scale on the arrowhead magnetisation of Bi2Sr2CaCu2Oy single crystals. G Yang, J S Abell, C E Gough. Physica C, Vol.282, No.Pt4, (1997) pp.2007-2008
      45. The effects of Al substitution on the microstructure and properties of laser-ablated epitaxial YBCO films on (001) MgO, M. Yeadon, P. Hirst, K. Locherer, J. Chrosch, J.S. Abell, M. Aindow, F. Wellhofer and E. Salje, Physica C 274 (1997)
      46. Monoclinic 2212-BSCCO single crystals: Phase evolution, superconductivity and doping studies, G. Yang, P. Shang, I.P. Jones, J.S. Abell, C.E. Gough, Physica C, Vol.282, No.Pt2, pp.1093-1094 (1997)
      47. The Effects of Al Substitution on the Microstructure and Properties of Laser-Ablated Epitaxial YBa2Cu3O7-d Films on (001) MgO, M. Yeadon, P.J. Hirst, K.R. Locherer, J. Chrosch, J.S. Abell, M. Aindow, F. Wellhöfer and E.K.H. Salje, Physica C Vol.274, No.1-2, pp.117-124 (1997)
      48. Topographical development and misfit relief in laser-ablated heteroepitaxial YBCO thin films., M. Yeadon, M. Aindow, F. Wellhofer and J.S. Abell, Journal Of Crystal Growth, Vol.172, No.1-2, pp.145-155 (1997)
      49. Investigation of critical currents in YBCO tracks over steps in SrTiO3 substrates using low temperature SEM beam induced voltage contrast. S.A.L. Foulds, J.S. Abell, D.J. Kang, E.J. Tarte. IEEE Transactions On Applied Superconductivity, Vol.7, No.2 Pt2, pp.2142-2145 (1997)
      50. Aluminium segregation of TiAl during single crystal growth. Y.J. Bi, J.S. Abell. Scripta Materialia, Vol.37, No.6, pp.743-752 (1997)
      51. Utilisation of beam-blanking in electron beam induced voltage contrast studies of high-Tc superconducting thin films. S.A.L. Foulds, J.S. Abell. Institute Of Physics Conference Series, No.153, pp.61-64 (1997)
      52. TEM study of YBCO thin film multi-layer devices, M.A. Barnett, J.S.Abell, M.Aindow, N.G. Chew, P.J.Hirst and R.G. Humphreys, MRS Proceedings (1997)
      53. TEM study of facet junctions in YBa2Cu3O7-d PrBa2Cu3O7-d thin film patterned multilayer structures. M. Barnett, M. Aindow, J.S. Abell, P.J. Hirst, N.G. Chew, R.G. Humphreys. Institute Of Physics Conference Series, No.153, pp.417-420 (1997)
      54. STM surface modification of YBa2Cu3O7-d thin films. S.E. Johnson, M. Yeadon, M. Aindow, P. Woodall, F. Wellhofer, J.S. Abell. Institute Of Physics Conference Series, No.153, pp.437-440 (1997)
      55. Utilisation of beam blanking in electron beam-induced voltage contrast stuies of HTC superconducting thin films, S.A.L. Foulds and J.S. Abell, Inst Phys. Conf. Ser. 153 61-64 (1997)
      56. Magneto-optic and electron beam-induced voltage contrast studies of YBCO thin films. M. Zamboni, S.A.L. Foulds, S. Koishikawa, K. Matsumoto, M. Murakami, J.S. Abell. Institute Of Physics Conference Series, No.158, pp.85-88 (1997)
      57. The growth of YBa2Cu3O7-d and PrBa2Cu3O7-d over argon ion milled steps. P.J. Hirst, M. Barnett, N.G. Chew, J.S. Abell, M. Aindow, R.G. Humphreys. Institute Of Physics Conference Series, No.158, pp.185-188 (1997)
      58. Magnetic noise in YBCO thin films and its relationship to growth morphology. J. Smithyman, C. Muirhead, M. Aindow, F. Wellhofer, P. Woodall. IEEE Transactions On Applied Superconductivity, Vol.7, No.2 Pt2, pp.1624-1627 (1997)
      59. The effect of selected process parameters on laser ablated YBCO thin films on SrTiO3 substrates. F. Wellhofer, P. Woodall, D.J. Norris, M. Aindow, M. Slaski, L.G. Earwaker. Journal Of Alloys And Compounds, Vol.251, No.1-2, pp.123- 128 (1997)
      60. Mapping the variations in properties of PLD films of YBCO deposited over large areas. P. Woodall, F. Wellhofer, D.J. Norris, M. Aindow, L.G. Earwaker. Journal Of Alloys And Compounds, Vol.251, No.1-2, pp.172- 175 (1997)
      61. The effect of substrate vicinal offcut on the morphology and defect microstructure of YBa2Cu3O7-x thin films on (001)SrTiO3. D. Vassiloyannis, D.J. Norris, S.E. Johnson, M. Aindow, P. Woodall, F. Wellhofer. Institute Of Physics Conference Series, No.153, pp.449-452 (1997)
      62. A TEM study of secondary epitaxial orientations in laser-ablated YBa2Cu3O7-d thin films. D.J. Norris, M. Aindow. Institute Of Physics Conference Series, No.153, pp.441-444 (1997)
      63. Electron beam induced voltage contrast and modulated optical reflectance studies of YBCO thin, film resonators, S.A.L. Foulds, D. Almond, P. Nokrach, F. Wellhofer, P. Woodall and J.S. Abell, Sup. Sc. Techn. 11 (1998) 378-382.
      64. Magneto-optical characterisation of BSCCO single crystals, M. Zamboni, S. Koishikawa, M. Murakami, G. Yang and J.S. Abell, Proc. Int. Wkshp. Moscow, (1998)
      65. A study of the STM Surface Modification of YBCO Thin Films, S.E. Johnson, P. Woodall and J.S. Abell, Physica C submitted
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    PCES - Physical Characterisation and Enabling Science
    Professor C E Gough, Professor W F Vinen, Dr Chris Muirhead and Dr A I M Rae
     

    Magnetic Research and Characterisation: This component of the rolling grant programme supports the characterisation and research of magnetic and electrical properties of HTS materials underpinning almost all research activities within the Core Programme, the National Crystal Growth Facility, our EC Network programmes, and all other materials-based superconductivity research at Birmingham. In addition to routine VSM, SQUID, ac-susceptibility and electrical transport measurements. Physics has also provided a high resolution powder diffraction facility, which has been extensively used for detailed x-ray analysis of HTS crystals and thin films (Dr Ian Langford), and a Rutherford Back Scattering (RBS) facility (Dr Lindsay Earwaker), which has provided valuable information on the stoichiometry and uniformity of PLD thin films, but was not available after 1997 as the accelerator is being converted to a dedicated medical application. Around 300 samples a year are characterised on the VSM and ~ 200 on the SQUID susceptometer. The pie-charts illustrate the wide multidisciplinary usage of these facilities: note that a single "measurement" on the SQUID susceptometer may take ½ a day, whereas up to 6 measurements a day (24 hours) is often possible on the less sensitive but higher field VSM. Magnetic characterisation by SQUID magnetometry provides the necessary proof of existence of superconductivity in new materials synthesised by the chemists(10-24), without which new discoveries have no validity. These facilities have also been used for a number of collaborative research projects including : the "fishtail" and "arrowhead" magnetic anomalies in YBCO and BSCCO, and their dependence on doping and materials processing(1-4,6,7), the tetragonal to monoclinic phase transition in vacuum annealed BSCCO (19), and the electrical and magnetic properties of superlattice, multilayer structures and ultra-thin (a few unit cells) films (9). Considerable effort has recently been directed to the magnetic and superconducting transitions in hybrid HTS/colossal magneto-resistive sandwich structures for potential spin-injection physics (35). In addition, the magnetic characterisation facilities are used by many other researchers for routine characterisation, without specific citation to the PDRA (Slaski) supporting such characterisation.

    Fundamental and enabling science. Although this part of our programme was not funded by the EPSRC at the last roll in 1994,and we received no additional grants for activities in this area, we have used departmental and redirected funds within the rolling grant to maintain a vigorous research programme on fundamental and enabling science [25-34, including 2 PRB and 1 PRL papers], which have involved important additional input from Prof. W F Vinen FRS and C M Muirhead. Our main activities have included: problems relating to the symmetry of the superconducting order parameter, the microscopic origins of HTS, and the influence of magnetic structures (flux lines/pancakes/lattices/liquids, etc) on superconducting properties in applied fields. Highlights have included a detailed experimental and theoretical investigation of the anomalous "Paramagnetic Meissner effect" [30- PRB 53 12441 (1996)], proving that a p-junction model (spin reversal or d-wave in origin) cannot explain the phenomenon. Measurements (DRA CASE studentship) of the dynamic resistance of thin film microbridges over 9-orders range in magnitude, confirming universal scaling of the liquid-glass transition in films and identifying nucleation at the edges of films as a primary source of noise [29 -EUCAS 95]. Dr Alastair Rae led a computational project on the dynamics of 2-d flux lattice arrays in the presence of random pinning and thermal activation, demonstrating a clear distinction between regimes where the irreversibility line was determined by thermal activation and by a glass/liquid phase transition, in addition to confirming the existence of a low field, re-entrant liquid phase [26 - PRL 75, 1835, 12995]. 4-point measurements of the field dependent c-axis conduction in 50 micron square 2212-BSSCO single crystals [27, PRB 50, 6655, 1995] were shown to correlate with Ted Forgan?s neutron and muon determination of the 3d-2d flux lattice decomposition field.. This has led to a collaboration with Dr August Yurgens (Chalmers) involving 4-point measurements of the field dependence of c-axis tunnelling between individual CuO2 planes, in mesa structures lithographically patterned on the atomically flat, cleaved surface, of NCGF 2212-BSCCO crystals (paper to be submitted to PRL). We are currently developing our own mesa fabrication technology, using ion-beam milling and other clean-room facilities, in collaboration with the Device Physics programme. This is now the principal focus of our continuing research, aimed at elucidating the role of c-axis tunnelling in determining HTS normal and superconducting properties, and the development of a single crystal HTS device technology. This is based on the reproducible, intrinsic Josephson coupling between individual atomic planes. We will first fabricate and characterising single crystal rf and dc SQUIDs, with a vertical coulomb blockade array as a longer term objective.

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    Publications (1994-1998)

    Magnetic Properties

      1. Correlation of magnetic properties with structural defects in 2212-BSCCO crystals, G Yang, P Shang, S D Sutton, I P Jones, J S Abell and C E Gough, Physica B 194-196 (1994) 1543-1544.2
      2. Anomalous ac magnetic responses in an YBa2Cu3O7 crystal with H perpendicular to c, L.K.Heill, M.G.Karkut, M.Slaski, and K.Fossheim, Physica C, 235-240 (1994) 3191
      3. Magnetic identification of 3d to 2d decomposition transition in BSCCO 2212 single crystals, G Yang, J S Abell and C E Gough, Proceedings of the 7th International Workshop on Critical Currents in Superconductors, Alpbach, Austria, January 1994, published by World Scientific, pp264-267.
      4. Neutron diffraction and mSR of flux line lattice, decomposition into pancakes, magnetisation and pinning mechanisms in 2212-BSSCO single crystals, E M Forgan, R Cubitt, M T Wylie, G Yang and C E Gough, Invited Talk, 1994 International Workshop on Superconductivity, Kyoto, Japan, 6-9th June, 1994 (invited Talk)
      5. Anisotropic strong pinning in melt-processed YBa2Cu3O7, L K Heill, M G Karkut, M Slaski, L T Sagdahl & K Fossheim, Proceedings of the 7th International Workshop on Critical Currents in Superconductors, Alpbach, Austria, January 1994, published by World Scientific, pp403-406.
      6. Magnetisation measurements on 2212 BSCCO single crystals - anomalies at the irreversibility temperature, M Slaski, G Yang, C M Muirhead & C E Gough, Proceedings of the 7th International Workshop on Critical Currents in Superconductors, Alpbach, Austria, January 1994, published by World Scientific, pp125-128.
      7. Magnetic identification of 3d to 2d vortex transitions in Bi2Sr2CaCu2Ox single crystals, G Yang, C E Gough and J S Abell, Physica C 235-240 (1994) 2713-2714.
      8. Magnetisation, magnetic susceptibility and microwave surface impedance of (Y0.84Sr0.16)SrBaCu2.68(SO4)0.21Oy and (Y0.74Ca0.16Sr0.1)Sr1.5Ba0.5Cu2.74 (SO4)0.15Oy, M Slaski, C E Gough, A P Kharel, A Porch, P Slater, R A Jennings and C Greaves, EUCAS 95, pp1047-1050 (1995).
      9. Critical currents of laser-ablated thin and ultrathin YBCO films, M.Slaski, P.Woodall, F.Wellhofer, M.Yeadon, and C.E.Gough, Critical Currents in Superconductors", edited by T.Matsushita and K.Yamafuji, World Scientific, proceedings of the 8th IWCC - Kitakyushu, 1996, 423
      10. Magnetic levitation using a cryotiger cooler. C E Gough, R Saini, G Walsh, J P G Price, J S Abell, R Claridge. Institute of Physics Conference Series, No.158 (1997) pp.817-820
      11. Effects of a geometrical length scale on the arrowhead magnetisation of Bi2Sr2CaCu2Oy single crystals. G Yang, J S Abell, C E Gough. Physica C, Vol.282, No.Pt4, (1997) pp.2007-2008
    Characterisation
      1. Synthesis and the superconducting properties of the strontium copper oxy-fluoride Sr2CuO2F2+d, M Al-Mamouri, P P Edwards, C Greaves & M Slaski, Nature 369 (1994) 382-384.
      2. Se and Te substitutions in YSr2Cu3O7-d and [Y/Ce]2Sr2Cu3O9-y, P.R.Slater, C.Greaves, M.Slaski, E.Z.Kurmaev, S.Uhlenbrock, and M.Neumann, Physica C 231 (1994) 109
      3. Synthesis and superconducting properties of the fluorite block system [YCe]2Sr2-xBaxCu3O9-y substituted by oxy-anions (BO33-, SO42-, PO43-), P.R.Slater, C.Greaves, and M.Slaski, Physica C 235-240 (1994) 741,
      4. Monoclinic phase transformation and related (100) twinning in BSCCO single crystals, P Shang, G Yang, I P Jones, C E Gough and J S Abell, M2S-HTSC-4, Physica C 235-240 (1994) 533-534.
      5. Superconductivity up to 64 K in the copper oxyfluorides Sr2-xAxCuO2F2+y (A=Ca, Ba) prepared using NH4F as a fluorinating reagent, P.R.Slater, P.P.Edwards, C.Greaves, I.Gameson, M.G.Francesconi, J.P.Hodges, M.Al-Mamouri, and M.Slaski, Physica C 241 (1995) 151
      6. An improved route to the synthesis of superconducting copper oxyfluorides SRs-xAxCuO2F2+d (A = Ca, Ba) using transition metal difluorides as fluorinating reagents, P R Slater, J P Hodges, M G Francesconi, P P Edwards, C Greaves, I Gameson and M Slaski, Physica C 253 6-22 (1995).
      7. Properties of laser-ablated epitaxial thin and ultrathin YBa2Cu3O7-x films, M Yeadon, M Aindow, J S Abell, M Slaski, C E Gough, P Woodall and F Wellhöfer EUCAS 95pp991-994 (1995).
      8. An effective synthesis of HgBa2Ca2Cu3O8+y: the highest superconductor, G.B.Peacock, I.Gameson, M.Slaski, W.Zhou, J.R.Cooper, and P.P.Edwards, Advanced Materials, 7 (1995) 925
      9. Synthesis and Structure of the Calcium Copper Oxyfluoride, Ca2CuO2F2+ . M. Al-Mamouri, P.P. Edwards, C. Greaves, P.R. Slater and M. Slaski. J. Mater. Chem., 5 (1995) 913-916.
      10. Doping studies on the orthorhombic to monoclinic phase transformation in Bi2Sr2Ca1Cu2Oy, G Yang, P Shang, I P Jones, J S Abell and C E Gough, Physica C 260 (1996) 103 -110.
      11. Observation of superconductivity (Tc=50K) in a new tetragonal alkaline earth cuprate Sr0.8Ba1.2CuO3+d, synthesised at ambient pressure, J.P.Hodges, P.R.Slater, P.P.Edwards, C.Greaves, M.Slaski, G.Van Tendeloo, and S.Amelinckx, Physica C 260 (1996) 249
      12. The effect of selected process parameters on laser ablated YBCO thin films on SrTiO3 substrates, F.Wellhofer, P.Woodall, D.J.Norris, M.Aindow, M.Slaski and L.G.Earwaker, EMRS -1996 - Strassbourg - France
      13. Induction of superconductivity in pulsed laser ablated La2CuO4 thin films by post-deposition fluorination, S.T.Lees, M.O.Jones, P.P.Edwards, C.Greaves, F.Wellhofer, P.Woodall, I.Langford, and M.Slaski , Physica C 270, 305-310 (1996)
      14. Room temperature oxidation of La2CuO4 thin films, S.T.Lees, M.O.Jones, I.Gameson, P.P.Edwards, M.Slaski and E.Moran, Advanced Materials - in preparation
      15. Optimisation of fluorination conditions for La2CuO4 thin films, S.T.Lees, M.O.Jones, I.Gameson, P.P.Edwards, M.Slaski, I.Langford, F.Wellhöfer, and P.Woodall, Physical Rev B - in preparation
      16. Monoclinic 2212-BSCCO single crystals: Phase evolution, superconductivity and doping studies. G Yang, P Shang, I P Jones, J S Abell, C E Gough. Physica C, Vol.282, No.Pt2, (1997) pp.1093-109
    Fundamental and Enabling Science
      1. High temperature superconductors, C E Gough, Encyclopaedia of Advanced Materials, Eds. S Bloor, R J Brook, M C Flemings, S Mahajan, R W Cahn, pp993-1000 (Pergamon Press, Oxford, 1994).
      2. Computer simulations of flux motion in high temperature superconductors, M J Probert and A I M Rae, LT-20 Conference, August 1993, Eugene, Oregon, Physica C 205 (1995) 180-182.
      3. Field and temperature dependence of the c-axis critical current in 2212-BSCCO single crystals at the melting and 2d-decomposition fields, Sheng Luo and C E Gough, Phys Rev B 51 (1995) 6655-6662.
      4. Nature of the irreversibility line in high-temperature superconductors, M I J Probert and A I M Rae, Phys Rev Letts 75 (1995) 1835-1838.
      5. Noise measurement over the vortex glass transition in YBCO thin film microbridges, J E Porter, W F Vinen and R G Humphreys, EUCAS 95, pp1343-1346 (1995).
      6. Paramagnetic Meissner effect in high temperature superconductors: Experiments and interpretation, Y He, C M Muirhead and W F Vinen, Phys.Rev. B 53 18 (1996) 12441-12453.
      7. The interpretation of experimentally measured magnetic susceptibilities of a SQUID ring in terms of the quantum mechanics of a double Josephson junction. A.I.M.Rae. Supercond. Sci. Technol. 9, (1996) 34-42.
      8. The Paramagnetic Meissner Effect in BSCCO Powders. Y He, C M Muirhead and W F Vinen. Proc. LT21(Prague), Czech. Jnl. Phys. 46 (Suppl), (1996) 1221-1222. (Invited talk)
      9. The c-axis V-I Characteristics of 2212-BSCCO single crystals. Sheng Luo, Yusheng He and C E Gough. Proc. LT21(Prague), Czech. Jnl. Phys. 46 (Suppl), (1996) 1695-1696.
      10. Model of flux-line lattice melting in a crystal of finite thickness. A I M Rae. Proc. LT21(Prague), Czech. Jnl. Phys. 46 (Suppl), (1996) 1807-1808.
      11. Glass transition related Josephson junction network model for Bi:2212 single crystal. S Luo, Y S He, C E Gough. Physica C, Vol.282, No.Pt4, (1997) pp.2437-2438
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    FLS - Flux Lattice Studies
    Prof Ted Forgan and Dr Alastair Rae
     

    This programme has involved the use of low angle neutron diffraction and muon spin rotation to probe the local field within the bulk of high Tc superconductors and hence to elucidate the very rich magnetic phases of these materials. We shall not separate out the neutron and muon aspects of the programme, since the techniques are complementary, the experiments and their analysis are largely carried out by the same personnel, and are often on the same samples. It should be emphasised that many of the results described here are the result of collaborations with other institutions, but there has always been a major and often a leading Birmingham input of work and ideas.

    (a) Experiments on BSCCO

    Just before the period of the rolling grant, we obtained the first direct microscopic evidence for flux lattice melting in single crystals of BSCCO-2212, using both muSR and neutron scattering. The neutron experiment was successful because of our systematic studies with muons, which indicated the correct temperature and field ranges in which to observe a flux line lattice (FLL) in this material. We were able to push to the limit the resolution of the SANS instrument at Riso, which was the only suitable machine available to us at the time, in order to reach the low field required. Above 0.1 T, the FLL signal disappears, due to decomposition of flux lines into individually pinned pancake vortices. These experiments led to great interest and to a large number of invitations to speak at international conferences [e.g. 1,3,7] during the first year of the grant. However, most of the initial follow up work was done with muons, because at Oak Ridge there was insufficient resolution and intensity and the ILL was closed for repairs. With muons, we have been able to deepen our understanding of the FLL in BSCCO. The muSR technique was used for the first time to give information about the amplitude of thermal fluctuations of flux lines [9], and by fitting both the temperature dependence of the signal in the flux solid and the flux lattice melting curve, we could deduce a value for the Lindemann ratio which causes melting - a quantity which is usually taken as an unknown parameter ~ 0.1 to 0.3, which is adjusted to fit experiments. Furthermore, as a result of theoretical work by Blatter, it became clear that in very anisotropic layered superconductors, electromagnetic coupling of pancakes can be more important than Josephson coupling between the planes over most of the B-T phase diagram. Our muon results [Phys.Rev.B - in press] show that BSCCO is indeed in this limit, and that the crossover field at which decomposition occurs should be a function not of the anisotropy parameter but of the value of the penetration depth in the basal plane. Our recently published results on a range of samples [17] show that these ideas are supported by experiment.

    Once the ILL was restarted, we had sufficient resolution and intensity to take forward the SANS work on BSCCO. One of the important results is a non-monotonic temperature-dependence in the signal at fields where the flux lattice is beginning to decompose into pancakes. This can only understood if an increase in temperature is improving the perfection of the flux lattice, which implies that the pancakes are thermally depinning out of the dislocated state [15]. Theory by Nelson (PRL., in press) has been stimulated by this work. In addition, we see distinct signs of a first order FLL melting transition at low fields, but a second order (glass?) melting at high fields, above the crossover field. At low fields, our phase diagram agrees with that obtained by Zeldov from local magnetisation measurements; however, he sees a curving of the first order transition line to low temperatures, where it ends in a critical point, and no transition above the crossover field. Since we can actually see the flux lattice diffraction pattern, and its disappearance at the melting temperature in these high fields, we feel that our microscopic results [15, and to be published] give a reliable indication of the phases adopted in BSCCO. Not only is this work on the stability of flux lines of considerable scientific interest, it also is an important basis for understanding the pinning of flux lines in BSCCO.

    (b) Experiments on YBCO

    Apart from systematic measurements such as [8], most of the interest in YBCO is at high fields, where muSR is difficult to employ. Since ILL has reopened, we have had the necessary neutron intensity to follow the FLL SANS signal in YBCO to temperatures close to Tc, in order to determine if there were signatures of flux lattice melting in this region. Our sample is heavily twinned, so initial measurements were taken with the field at a large angle to the twin planes, in order to minimise the effects of pinning. However, later measurements with the field parallel to the c-axis have shown very similar results. In all cases at high fields, the flux lattice signal goes linearly to zero as the temperature is increased to the melting temperature [14 and to be published]. Thus, we see a second -order phase transition, which is doubtless related to the twin-plane pinning; however, the linear temperature-dependence represents a mean-field behaviour of the FLL order parameter, which is a challenge for theorists to explain. At low fields, the temperature-dependence of the signal is more nearly parabolic, approaching zero with zero slope: this is the behaviour to be expected in a superconductor approaching Hc2 when thermal fluctuations are negligible. In all cases, the melting temperature of the FLL in our twinned crystal, as a function of field and field direction, is identical to that seen by apparently first order changes in resistivity in untwinned crystals. However, in resistivity measurements, twinning smears out the transitions, whereas neutron diffraction still reveals unsmeared (but second-order) transitions. This shows the importance of using measurements (such as neutron diffraction) which record thermodynamic order, to reveal the true nature of the phase diagram. Above the phase transition in both BSCCO and YBCO the signal is zero; we can therefore state with certainty that in the flux liquid state the flux lines are not straight- otherwise we would observe a ring of scattering. This provides backup for the results of "flux transformer" geometry resistivity measurements. Indeed it appears that the melting transition is accompanied by a breakup of the flux lines into pancakes, so we may more accurately refer to the transition as "sublimation" . We have recently been able to acquire untwinned crystals from ISTEC which are of sufficiently large size and good quality to allow neutron measurements; initial indications are that the flux lattice phase transition becomes sharper in these crystals.

    (c) Scientific debate

    We have published a PRL comment [6], pointing out the defects in a Letter from a U.S. group, who unwisely claimed to have observed FLL melting in the middle of the mixed state in niobium. The same group later published some high-resolution observations of the FLL diffraction pattern in YBCO. They correctly interpreted these as due to several distorted triangular lattices coexisting within the sample, but foolishly ascribed the orientation and distortion to d-wave effects; this has misled many theoreticians into trying to reproduce their structures. We pointed out [10] that the orientation is controlled by twin planes, and the distortion is largely due to anisotropy between the a and b directions in the basal plane. Finally, we should mention that some respected theoreticians (eg M.A.Moore, preprint) claim that flux lattice melting never occurs, and the disappearance of diffraction spots represents a rapid crossover of length scales. An extremely sharp melting transition would represent a falsification of this theory: our experiments have not so far seen a sufficiently sharp transition to do this, and insofar as our measurements cast doubt on the local magnetisation data of Zeldov, his sharp transitions may also not represent a disproof.

    (d) Other achievements

    For information, we mention that we have been involved in neutron and muSR measurements on a variety of unconventional superconductors of current interest [2,4,13]; however, two other important high-Tc activities should be mentioned. The first is the thermodynamic consideration and modelling (with AIMR) of the spatially inhomogeneous state which is observed by local magnetisation measurements [12,20 and to be published]. It is clear from this work that the discussion in the literature of magnetisation jumps is far too simplistic. In addition, we have performed simulations of flux pinning and flow [18,19] which have nicely shown the relationships between single and collective pinning, and TAFF and vortex glass melting, and have also predicted that moving flux lines can be more ordered than static pinned ones.

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    Publications (1994-1998)

    1. M.Yethiraj, H.A.Mook, E.M.Forgan, R.Cubitt, M.T.Wylie, D.M.Paul, S.L.Lee, J.Ricketts, P.H.Kes and K.Mortensen. (1994). "Small-angle neutron-scattering study of the flux line lattice in a single crystal of Bi2Sr2CaCu2O8+x". J.Appl.Phys. 76, 6784-7.
    2. R.Cywinski, Z.P.Han, R.Bewley, R.Cubitt, M.T.Wylie, E.M.Forgan, S.L.Lee, M.Warden and S.H.Kilcoyne.(1994). "A m SR determination of the penetration depth in superconducting YNi2B2C". Physica C 233, 273-80.
    3. E.M.Forgan, R.Cubitt, M.T.Wylie, G.Yang, S.L.Lee, H.Keller, D.McK.Paul, M.Yethiraj, H.A.Mook and P.H.Kes.(1994) "Studies by neutron diffraction and m SR of flux lattice orientation, pinning, melting and decomposition in high-Tc superconductors". Proc 7th International Workshop on Critical Currents in Superconductors, ed H.W.Weber, pp21-26 (World Scientific 1994)
    4. S.Lee, M.Brunner, H.Keller, M.Warden, D.Zech, R.Bewley, R.Cywinski, Z.P.Han, R.Cubitt, E.M.Forgan, M.T.Wylie and S.H.Kilcoyne. (1994). "m SR investigation of the superconducting properties of YNi2B2C". Physica C 235, 2535-6.
    5. R.Cubitt, E.M.Forgan, M.T.Wylie, G.Yang, S.L.Lee, H.Keller, D.M.Paul, H.A.Mook, M.Yethiraj, P.H.Kes, T.W.Li, A.A.Menovsky, Z.Tarnawski and K.Mortensen. (1994). " Small-angle neutron diffraction studies of vortex structures in high-temperature superconductors". Physica C 235, 2583-4.
    6. E.M.Forgan, R.Cubitt, M.Yethiraj, D.K.Christen, D.M.Paul, S.L.Lee and P.L.Gammel. 1995. "Comment on 'Vortex dynamics and melting in niobium' ". Phys.Rev.Lett. 74, 1697.
    7. E.M.Forgan, R.Cubitt, M.T.Wylie, S.L.Lee, H.Keller, D.McK.Paul, M.Yethiraj, H.A.Mook P.H.Kes, T.W.Li, A.A.Menovsky, Z Tarnawski, N.Koshizuka, J.Ricketts and K.Mortensen.(1994) "Observation of the flux line lattice by neutron diffraction and muon spin rotation". Proc ISS-94 (Advances in Superconductivity, VII, eds. K.Yamafuji and T.Morishita, pp 413-418, Springer, 1995)
    8. P.Zimmermann, H.Keller, S.L.Lee, I.M.Savic, M.Warden, D.Zech, R.Cubitt, E.M.Forgan, E.Kaldis, J.Karpinski and C.Kruger. 1995. "Muon-Spin-Rotation Studies of the Temperature-Dependence of the Magnetic Penetration Depth in the YBa2Cu3Ox Family and Related-Compounds", Physical Review B-Condensed Matter 52, 541-552.
    9. S.L.Lee, M.Warden, H.Keller, J.W.Schneider, D.Zech, P.Zimmermann, R.Cubitt, E.M.Forgan, M.T.Wylie, P.H.Kes, T.W.Li, A.A. Menovsky and Z.Tarnawski. 1995. "Evidence for 2-Dimensional Thermal Fluctuations of the Vortex Structure in Bi2Sr2CaCu2O8+d from Muon Spin Rotation Experiments", Physical Review Letters 75, 922-925.
    10. E.M.Forgan and S.L.Lee. 1995. "Vortex Lattice Symmetry and Electronic-Structure in YBa2Cu3O7", comment in Physical Review Letters 75, 1422.
    11. D.M.Paul, E.M.Forgan, R.Cubitt, S.L.Lee, M.Wylie, H.A.Mook, M.Yethiraj and K.Mortensen. 1995. "Neutron-Scattering From The Flux-Line Lattice In Bi2Sr2CaCu2O8+g", Physica B 213, 107-109.
    12. D.E.Farrell, E.Johnston-Halperin, L.Klein, P.Fournier, A.Kapitulnik, E.M.Forgan, A.I.M.Rae, T.W.Li, M.L.Trawick, R.Sasik and J.C.Garland. 1996. "Magnetization Jumps and Irreversibility in Bi2Sr2CaCu2O8", Physical Review B-Condensed Matter 53, 11807-11816.
    13. A.Huxley, R.Cubitt, D.McPaul, E.Forgan, M.Nutley, H.Mook , M.Yethiraj, P.Lejay and J.M.Penisson. 1996. "A neutron study of the flux lattice in the superconductor CeRu2.", Physica B 224, 169-171
    14. M.T.Wylie, E.M.Forgan, S.Lloyd, S.Lee, R.Cubitt, M.Yethiraj and H.A.Mook. 1996. "Observation of flux lattice melting in YBCO by small angle neutron scattering", Proc LT-21: Czech J.Phys 46, Suppl.S3, 1569-70
    15. E.M.Forgan, M.T.Wylie, S.Lloyd, S.L.Lee and R.Cubitt. 1996. "Observation of a re-emergence of the flux lattice in BSCCO", Proc LT-21: Czech J.Phys 46, Suppl.S3, 1571-2.
    16. P.H.Kes, H.Pastoriza, T.W.Li, R.Cubitt, E.M.Forgan, S.L.Lee, M.Konczykowski, B.Khaykovich, D.Majer, D.T.Fuchs, E.Zeldov. 1996. "Flux lattice melting and dimensional crossover in Bi-2212 single crystals", Journal de Physique I, 6, 2327-2354.
    17. C.M.Aegerter, S.L.Lee, H.Keller, E.M.Forgan, S.H.Lloyd. 1996 "Dimensional Crossover in the magnetic phase diagram of Bi2.15Sr1.85CaCuO8+d crystals with different oxygen stoichiometry" Phys.Rev.B 54, 15661-15664
    18. M.J.Probert and A.I.M.Rae. 1995 "Computer simulations of flux motion in high temperature superconductors", Physica C 205, 180-182.
    19. M.J.Probert and A.I.M.Rae. 1995 "The nature of the irreversibility line in high temperature superconductors", Physical Review Letters 75, 1835-1838.
    20. A.I.M.Rae. 1996. "Model of flux lattice melting in a crystal of finite thickness", Proc LT-21: Czech J.Phys 46, Suppl.S3, 1807-1808.
    21. A.I.M.Rae. 1996. "Interpretation of experimentally measured susceptibilities of a SQUID ring in terms of the quantum mechanics of a double Josephson junction", Supercond.Sci.Technol. 9, 34-42.
    22. S.L. Lee, C.M. Aegerter, H. Keller, M. Willemin, B. StaublePumpin, E.M. Forgan, S.H. Lloyd, G. Blatter, R. Cubitt, T.W. Li, P. Kes. 1997. "Role of electromagnetic coupling in the low-field phase diagram of Bi2.15Sr1.85CaCu2O8+d ." Physical Review B-Condensed Matter, 55, No.9, pp.5666- 5669
    23. S.L. Lee, S.J. Blundell, F.L. Pratt, P.A. Pattenden, E.M. Forgan, T. Sasaki, C.M. Aegerter, M. Hunt, K.H. Chow, W. Hayes, J. Singleton, H. Keller, I.M. Savic. 1997. "Muon-spin rotation studies of the flux lattice in kappa-(BEDT- TTF)(2)Cu(SCN)(2)". Synthetic Metals, 85, No.1-3, pp.1495-1496
    24. E.M. Forgan, M.T. Wylie, S. Lloyd, M.P. Nutley, S.L. Lee, R. Cubitt, C. Aegerter, H. Keller, T.W. Li. 1997. "m SR studies of the vortex lattice in high-T-c and other superconductors". Hyperfine Interactions, 105, No.1-4, pp.61-69
    25. M. Yethiraj, D.M. Paul, C.V. Tomy, E.M. Forgan. 1997. "Neutron scattering study of the flux lattice in YNi2B2C". Physical Review Letters, 78, No.25, pp.4849-4852
    26. S.L. Lee, F.L. Pratt, S.J. Blundell, C.M. Aegerter, P.A. Pattenden, K.H. Chow, E.M. Forgan, T. Sasaki, W. Hayes, H. Keller. 1997. "Investigation of vortex behavior in the organic superconductor kappa-(BEDT-TTF)(2)Cu(SCN)(2) using muon spin rotation". Physical Review Letters, 79, No.8, pp.1563-1566
    27. C.M. Aegerter, J. Hofer, I.M. Savic, H. Keller, S.L. Lee, C. Ager, S.H. Lloyd, E.M. Forgan. 1998. "Angular dependence of the disorder crossover in the vortex lattice of Bi2.15Sr1.85CaCu2O8+d by muon spin rotation and torque magnetometry". Physical Review B-Condensed Matter, 57, No.2, pp.1253- 1258
    28. D.M. Paul, C.V. Tomy, C.M. Aegerter, R. Cubitt, S.H. Lloyd, E.M. Forgan, S.L. Lee, M. Yethiraj. 1998. "Nonlocal effects and vortex lattice transitions in YNi2B2C". Physical Review Letters, 80, No.7, pp.1517-1520
    29. S.L. Lee, C.M. Aegerter, C. Ager, E.M. Forgan, S.H. Lloyd, H. Keller. 1998. "Muon-spin rotation (m SR) measurements on Bi2Sr2CaCu2O8+d in the presence of columnar defects". Journal Of Magnetism And Magnetic Materials, 177, No.Pt1, pp.523-524
    30. C. Ager, S.L. Lee, C.M. Aegerter, F. Pratt, S.J. Blundell, S.H. Lloyd, T. Sasaki, E.M. Forgan, H. Keller. 1998. "Angular-dependent muon-spin rotation on the mixed state of the organic superconductor K-(BEDT-TTF)(2)CU(SCN)(2)". Journal Of Magnetism And Magnetic Materials, 177, No.Pt1, pp.561-562
      Return to Contents 
    DP - Device Physics
    Dr Chris Muirhead
     
     
    The programme during the last three years has been focused on a number of problems relating to flux motion and noise in thin films and devices, with a view to understanding the underlying physics and limitations on performance of current HTS devices. Over the last two years Dr Mark Colclough, an EPSRC Advanced Fellow, has been playing an increasing role in helping us to develop our clean room and microfabrication facilities in parallel with his development of a scanning SQUID microscope, which will play an increasingly important role in our future programmes in our device physics programme.

    Significant advances have been:

    The programme over the last 3 years has been an extension of our earlier work on flux motion at the quantum scale and our joint work on HTS SQUID devices. CMM was responsible for the design of the PLDF and has provided academic and technical support since its inception in 1992.

    During the last year, CMM and MSC have designed and commissioned a small clean room (overall class 1000 but around 10 in the lithography areas), with accurate temperature and humidity control. It is equipped with facilities for optical lithography including a mask aligner and ion beam miller with in-situ sputtering. This now supports not only the Device Physics and Fundamental Science parts of our thin film programme, but also the active-device microwave work with Electrical Engineering, and samples for EBIV microscopy in Metallurgy. We have also developed a unique SQUID voltmeter system, which can be switched rapidly between the high and low current parts of a junction characteristic, to investigate correlations between critical current and resistive noise, which is very sensitive to the underlying physics of junctions.

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    Publications (1994 - 1998)

    1. A Flett, Y He, C M Muirhead, M S Colclough and K Char. An investigation of flux noise processes in biepitaxial YBCO junctions. Physica B, 87-8, 194-6 (1994)
    2. S A Foulds, C M Muirhead and R G Humphreys Flux noise in an epitaxial thin film YBCO ring close to the superconducting transition temperature. Physica B 194-6, 1619-20 (1994)
    3. L B Kiss, P Svedlindh, M BjÜrnander, P Norblad, C M Muirhead, J Smithyman, U Klein and Z Gingl. Why is noise so strong in high temperature superconductors ?Invited paper at the 13th International Conference on Noise in Physical Systems. World Scientific, 105-111 (1995)
    4. M Druoet, S A Foulds, L B Kiss, U Klein, J Smithyman, C M Muirhead, F Wellhöfer and P Woodall. Magnetic noise properties of YBCO/PBCO superlattices. IEEE Transactions on Magnetics, 2973-5 (1995)
    5. A Flett, M S Colclough, Y He, C Muirhead, R A Robinson and K Char. Voltage-current characteristics and noise properties of SNS junctions. IEEE Transactions on Applied Superconductivity, Vol 5, No 2, (1995)
    6. L B Kiss, U Klein, J Smithyman, C M Muirhead, F Wellhöfer and P Woodall. Experimental study of flux noise in YBCO/PBCO superlattices. IOP Conference Series, 148, 1027-30 (1995)
    7. R A Robinson, C M Muirhead and U. Klein. Noise properties of integrated microwave SQUIDs. IOP Conference Series, 148, 1629-32 (1995)
    8. L B Kiss, U. Klein, C M Muirhead, J Smithyman and Z Gingl. Diffussive fluctuations, Long and short-time cross correlations in the motion of vortex pancakes in different layers of YBCO/PBCO superlattices. Solid State Communications, Vol. 101, No 1, 51-56 (1997)
    9. S A L Foulds, J Smithyman, G F Cox and C M Muirhead. Magnetic flux noise in superconducting rings and discs close to the superconducting transition. Physical Review B, 9 pages, April 97.
    10. J Smithyman, C M Muirhead, M Aindow, F Wellhöfer and P Woodall. Magnetic noise in thin films and its relationship to growth morphology. IEEE Transactions on Applied Superconductivity, Vol 7 No.2 Pt2, pp.1624-1627 (1997)
    11. M A Bari, O Cabeza, L Capogna, P Woodall and C M Muirhead. Conduction mechanisms in c-axis oriented YBCO base trilayer junctions with ferromagnetic A0.7B0.3MnO3 magnetite barriers. IEEE Transactions on applied superconductivity, Vol 6 (In print)
    12. A.H. Miklich, D. Koelle, T.J. Shaw, F. Ludwig, D. T. Nemeth, E. Dantsker, J. Clarke, N. McN. Alford, T.W. Button, M. S. Colclough; Low-frequency excess noise in YBa2Cu3O7-x dc superconducting quantum interference devices cooled in static magnetic-fields . Appl. Phys. Lett. 64 3494-3496 (1994).
    13. K.E. Myers, K. Char, M.S.Colclough, T.H. Geballe; Noise characteristics of YBa2Cu3O7-d / CaRuO3 / YBa2Cu3O7-d Josephson junctions .Appl. Phys. Lett. 64 788-790 (1994).
    14. A. Flett, Y. He, C.M. Muirhead, M.S. Colclough, K. Char; An investigation of flux noise processes in biepitaxial YBCO junctions. Physica B 194 87-88 (1994).
    15. A. Flett, M.S. Colclough, Y. He, C.M. Muirhead and R.A. Robinson, K. Char; Voltage-current characteristics and noise properties of SNS junctions IEEE Trans. appl. superconductivity 5 2973-2975 (1995).
    16. L.P. Lee, M. Teepe, V. Vinetskiy, R. Cantor and M.S. Colclough; Key elements for a sensitive 77 kelvin dc SQUID magnetometer. Appl. Phys. Lett. 66 3059-3061 (1995).
    17. M.S. Colclough; New image for SQUIDs. Physics World 8 33-34 (1995).
    18. M.S. Colclough. The SQUID magnetometer: an application of thin film superconductors. In "Science and technology of thin films"; eds. F.C. Matacotta and G. Ottaviami, World Scientific (1995)
    19. M.S. Colclough. SQUID control apparatus with non-cryogenic flux-locked loop disposed in close proximity to the SQUID; US Pat. 5532592, 1996.
    20. C.C. Speake, C. Trenkel and M.S. Colclough; Force and force gradients due to trapped flux in superconducting accelerometer. Fundamental physics in space symposium 1996 ed. R. Reinhard. (submitted)
    21. M.J. Barker and M.S. Colclough; A two-dimensional capacitive position sensor with rotation output. Review of Scientific Instruments, Vol.68, No.8, pp.3238- 3240 (1997)
    22. M.A. Bari, O. Cabeza, L. Capogna, P. Woodall, C.M. Muirhead, M.G. Blamire. Conduction mechanisms in c-axis oriented YBCO based trilayer junctions with ferromagnetic A(0.7)B(0.3)MnO(3) manganite barriers. IEEE Transactions on Applied Superconductivity, Vol.7, No.2 Pt3, pp.2304-2307 (1997)
    23. S.A.L. Foulds, J. Smithyman, G.F. Cox, C.M. Muirhead, R.G. Humphreys. Magnetic flux noise in superconducting rings and disks close to the superconducting transition. Physical Review B-Condensed Matter, Vol.55, No.14, pp.9098-9106 (1997)
    24. F. Wellhöfer, P. Woodall, D.J. Norris, S. Johnson, D.Vassiloyannis, M.Aindow, M. Slaski and C.M. Muirhead. The effect of substrate-off-cut on the properties of epitaxial thin films of Yba2Cu3O7- grown by pulsed laser deposition. Accepted for publication in Surface Science.
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    TFM - Textured Film Materials
    Professor Stuart Abell and more recently Dr Tim Button
     

    Thick film processing has formed a central part of the Superconducting Materials Group (SMG) programme at Birmingham (led by Prof J S Abell) since work on superconducting oxides began, and has been successfully reviewed and supported at each renewal of the rolling grant. The Birmingham thick film programme is the most successful in the UK and progress is comparable with the best in the world in this area. The close collaboration over the years with ICI has taken on a new dimension since the last review with the incorporation of the ICI group into the IRC /School as the Functional Materials Group (FMG) led by Dr T W Button. This interaction has been and will continue to be complementary.

    During the last three years our understanding of YBCO thick film materials has increased enormously, leading to dramatic improvements in properties and one of the first applications of HTS technology into the commercial market as outlined below. The influence of flux pinning additions to YBCO films deposited on YSZ substrates has been studied. These include BaSnO3, CeO2 and BaZrO3. Higher Jc values have been attributed to microstructural modifications associated with these additions, for example the observation of 10nm BaSnO3 particles and defects at particle/matrix interfaces 13. A systematic study of Pt doping (Johnson Matthey CASE) has shown that Jc values can be enhanced by a factor of 4, when optimally doped and is the subject of a patent application. The addition of Pt, either in elemental or compound form, acts to refine the 211 size and distribution, thus controlling the generation of dislocation networks, providing flux pinning centres 16,17,20,22,26.

    The RF properties of the films have been improved and the surface resistance Rs values are now only a factor of 5 larger than the best epitaxial thin films, and have comparable RF power dependence 28,30,36,38,39,41,42,43. This has led to a particularly notable achievement during the last year where YBCO thick film filters, manufactured using technology developed in Birmingham, have been successfully tested in cellular communications base stations in the US by Illinois Superconductor Corporation. These filters are now available commercially.

    Microstructural characterisation by XRD, SEM and TEM has played a central role in our understanding of features responsible for improved properties and, in collaboration with Cambridge, has led to a model of current flow in these materials 2,3,8,31. More recent work has focused on the fabrication of NdBCO films, following reported enhanced properties in bulk material due to novel pinning centres. Preliminary work employing reduced partial pressure processing has achieved Tc of 90K with Jc values of a few hundred Acm-2. Plasma sprayed layers of YSZ, Y2O3 and BaZrO3 deposited on alumina substrates have proved to be effective barriers against Al3+ diffusion, thus creating the possibility of incorporating these and other technical substrates in RF and microwave device design 6,14,21.

    Alternative film deposition techniques based on dip pyrolysis and sol-gel routes have demonstrated the potential for chemical routes, which are particularly encouraging for scaling up to large area coverage 7. A value of Jc=2x104 Acm-2 for YBCO on Ag substrates has been obtained by the pyrolysis route 7, and the process has been patented. These approaches form the basis of a recently awarded British Council / DAAD Academic Research Collaboration grant between Birmingham and IFW Dresden which will provide a focus for the potential of these techniques.

    Considerable interest is developing in the use of thick film components in power engineering applications such as fault current limiters and discussions are in progress with a number of companies as to possible ways of exploiting the technology in this application area. For example GEC have supported a feasibility study at the University, and Birmingham are partners with them and BICC, Oxford Instruments and Southampton University in a DTI proposal to design and build a demonstrator power network system, incorporating an inductive FCL design. Rolls Royce are supporting a CASE award in materials development for a resistive FCL design, which involves a collaboration with the IRC Cambridge. In collaboration with the School of Elec. Eng. a prototype inductive FCL device has been fabricated with YBCO thick films as the superconducting element. Thick films have several advantages in such a device, for example, good heat dissipation characteristics due to their large surface area, the YSZ substrate provides considerable mechanical support, and the components can be stacked up and easily replaced if necessary 25.

    Other applications being actively pursued exploit the good RF and DC properties, low flux noise and low phase noise characteristics 44 of the films and include high Q resonators, low noise magnetic shields 27,33, large area antennas 40 and flux transformers. The continued success of the combined Birmingham thick film programme has been instrumental in generating additional external funding of over £100k per annum during the last few years, and we are involved in a large number of collaborations in the UK (IRC Cambridge, UMIST, South Bank, Portsmouth, GEC, Elec.Eng, Oxford Instruments, Nottingham,NPL) , Europe (EURUS, Thomson, KFA Julich, IFW Dresden) and the USA (UC Berkeley, Los Alamos, Conductus, AEL Industries, U Houston, Kalamzoo, IBM, ISC, Amuneal, EURUS) aimed at developing HTS thick films and bulk materials (e.g. current leads 29,35) for applications.

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    Publications (1994-1998)

    1. A compositional and structural study of the phase Ba(Zr,Cu)O3, A. Marshall, T.C. Shields and J.S. Abell, J. Mater. Sci., 29 (1994) 1930-1934.
    2. Transport and Magnetic Critical Current Measurements in Melt Processed YBCO Thick Films, A.R. Jones, D.A. Cardwell, N.J.C. Ingle, S.P. Ashworth, A.M. Campbell, N. Alford, T.W. Button, F. Wellhofer and J.S. Abell, Proc. IWCC, Alpbach (1994) 109-112.
    3. Investigation of the Critical State in Melt Processed YBCO Thick Films, D.A. Cardwell, A.R. Jones, N.J.C. Ingle, A.M. Campbell, T.W. Button, N. Alford, F. Wellhofer and J.S. Abell, Cryogenics 34 (1994) 671-677.
    4. Critical Currents in BSCCO 2212 Fibres, R.G.L. Hodges and J.S. Abell, Proc. IWCC Alpbach (1994) 459-462.
    5. Infra-red thermal imaging of hot zones produced in BSCCO glass precursors by DCZ, J.R. Bhakta, I.R. Harris, J.S. Abell and P.W. Webb, Physica C 235-240 (1994) 535-536.
    6. Reactive formation Of YBCO thick films on Y2O3 substrates, T.C. Shields and J.S. Abell, Ibid. 391-392.
    7. Preparation of YBCO films on YSZ and silver substrates by the Dipping Pyrolysis Process, H. Yokota and J.S. Abell, Ibid. 629-630
    8. Correlation of transport and magnetic critical currents in melt processed YBCO thick films, A.R. Jones, D.A. Cardwell, N.J.C. Ingle, S.P. Ashworth, A.M. Campbell, N. Alford, T.W. Button, F. Wellhofer and J.S. Abell, J. Appl. Phys. 76 (1994) 1720-1725
    9. The Bi2O3 - SrO3 Phase Diagram, E.Y. Vstavskaya, A.Y. Zuev, V.A. Cherepanov, S.D. Sutton and J.S. Abell, J. Phase Equilibria 15 (1994) 573-577.
    10. The Phase Diagram of the Bi- Sr - Cu - O System, E.Y. Vstavskaya, V.A. Cherepnov, A.Y. Zuev, S.D. Sutton and J.S. Abell, J. Materials Chem. 4 (1994) 1871-1873.
    11. Physical and microstructural properties of low resistance contacts to YBCO, C.A. Hollin and J.S. Abell., Superconductor Science and Technology 8 (1995) 6-14.
    12. Influence of the Mould temperature on the properties of Melt Cast BSCCO Precursors, J. Bhakta, I.R. Harris and J.S. Abell, IEEE Trans. Appl. Supercond. 5 (1995) 1482-1485.
    13. A study of YBCO thick films with BaSnO3 additions, T.C. Shields. T.J. Gray, Y.J. Bi and J.S. Abell, PhysicaC 249 (1995) 387- 395.
    14. Production of superconducting ceramic YBCO thick films by reaction of eutectic melts with yttria substrates., T.C. Shields and J.S. Abell, British Ceramic Proceedings : Ceramic Films and Coatings 54 (1995) 249-259.
    15. Texture formation in silver-sheathed Bi-based superconducting tapes, J. Jiang and J.S. Abell, Inst. Phys. Conf. Ser. 148 (1995) 407-410.
    16. Enhanced properties in screen printed YBCO thick films with additions of platinum and/or Ba4Cu1+xPt2-xO9z, J. Langhorn, Y.J. Bi and J.S. Abell, Ibid. 199-202.
    17. Improved Microstructural features in screen printed YBCO thick films with Pt additions, J. Langhorn, Y.J. Bi and J.S. Abell, Inst. Phys. Conf. Ser. 147 (1995) 413-416
    18. The effects of precursor powder on the texture formation in BSCCO/Ag tapes, J. Jiang and J.S. Abell, Proc. TMS Meeting, Anaheim( 1996) 13-21.
    19. In-situ kinetic neutron diffraction study of melt cast BSCCO rods under an applied dc field, P.S. Whitfield, J. Bhakta, J.S. Abell, Ibid. 197-202
    20. Enhanced properties in screen printed YBCO thick films with doping additions of Pt and Rh, J. Langhorn, Y.J. Bi and J.S. Abell, Ibid. 269-274.
    21. YSZ barrier layers by atmospheric plasma spraying, S.C. Watcham and J.S. Abell, Ibid. 241-248.
    22. Platinum group metals as flux pinning additions in screen printed superconducting YBCO thick films, J.B. Langhorn, Y.J. Bi and J.S. Abell, Physica C, 271 (1996) 164-170.
    23. Preparation of superconducting BSCCO by radiative and novel electrical resistance heat treatment of melt cast precursor rods, J.S. Abell and J.R. Bhakta, Chapter in Superconducting Glass-Ceramics in BSCCO : Fabrication and Application, World Scientific, in press
    24. A H Miklich, D Koelle, T J Shaw, F Ludwig, D T Nemeth, E Dantsker, J Clarke, N McN Alford, T W Button and M S Colclough, "Low-frequency excess noise in YBa2Cu3O7-x dc Superconducting Quantum Interference Devices Cooled in Static Magnetic Fields", Appl Phys Lett, 64 (1994), 3494-3496.
    25. T W Button, N McN Alford and P A Smith, "Melt processed YBa2Cu3O7 Thick Films", Proc 8th Cimtec World Ceramics Congress, Forum on New Materials, Florence, Italy, 29 June - 4 July 1994.
    26. N McN Alford, T W Button, S J Penn and P A Smith, "YBa2Cu3Ox Low Loss Current Leads", Proc 8th Cimtec World Ceramics Congress, Forum on New Materials, Florence, Italy, 29 June - 4 July 1994.
    27. P A Smith, N McN Alford and T W Button, "Radio-Frequency Power Performance of Thick Films and Bulk Melt Textured YBCO", Proc 8th Cimtec World Ceramics Congress, Forum on New Materials, Florence, Italy, 29 June - 4 July 1994.
    28. N J C Ingle, D A Cardwell, A R Jones, F Wellhofer and T W Button, " The Effect of Thickness on the Magnetic Properties of Melt Processed YBCO Thick Films", Supercond Sci Tech, 8 (1995) 282-290.
    29. W A Phillips, D Jedamzik, K Lamacraft, S Zammattio, R B Greed, S J Hedges, P R Whitehead, B F Nicholson, T W Button, P A Smith, N McN Alford, N Peters and J Grier, "An Integrated 11GHz Cryogenic Downconvertor", Presented at ASC 94, Boston, IEEE Trans Applied Superconductivity, Vol 5 No 2, (1995) pp 2283-2286.
    30. F Ludwig, E Dantsker, R Kleiner, D Koelle, J Clarke, S Knappe, D Drung, H Koch, N McN Alford and T W Button, "Integrated High-Tc Multiloop Magnetometer", Appl Phys Lett, 66 (1995) 1418-1420.
    31. M Hosking, Y G Proykova, A Hewitt, N McN Alford and T W Button, "A Superconducting and Integrated Microwave Transmitter and Receiver in Microstrip Using Thick Film YBCO", Presented at ASC 94, Boston, IEEE Trans Applied Superconductivity, Vol 5 No 2 (1995) pp 2287-2290.
    32. N McN Alford, T W Button, S J Penn and P A Smith, "YBa2Cu3Ox Low Loss Current Leads", Presented at ASC 94, Boston, IEEE Trans Applied Superconductivity, Vol 5, No 2 (1995) pp 809-812.
    33. S J Penn, T W Button, P A Smith and N McN Alford, "Radio-frequency and Low Noise Performance of YBCO Thick Films", Presented at the European Conference on Applied Superconductivity EUCAS 95, Edinburgh, Scotland, 3-6 July 1995, Applied Superconductivity 1995, Ed D Dew-Hughes, IOP Publishing, Bristol, pp1051-1054 (1995).
    34. T W Button, P A Smith, N McN Alford, R B Greed, M J Adams and B F Nicholson, "Low Phase Noise Oscillators incorporating YBCO Thick Film Cavity Resonators", Presented at the European Conference on Applied Superconductivity EUCAS 95, Edinburgh, Scotland, 3-6 July 1995.
    35. S K Remillard, L J Klemptner, J D Hodge, T A Freeman, P A Smith and T W Button, "Generation of Intermodulation Products by Granular YBa2Cu3O7-x Thick Films", Presented at the SPIE 1995 International Symposium on Optical Science, Engineering and Instrumentation, 9-14 July 1995, San Diego, SPIE Proceedings, Vol 2559 (1995) pp59-68. .
    36. N McN Alford, S J Penn, T W Button and P A Smith, "Thick Film Applications of High Temperature Superconductors", Presented at IEE Meeting on Practical Applications of High Temperature Superconductors, London, 4 May 1995.
    37. D Lacey, G Drossos, Z Wu, L E Davis, T W Button and P A Smith, "Miniaturised HTS Microstrip Patch Antenna with Enhanced Capacitive Loading", Presented at the IEE Colloquium, "Superconducting Microwave Circuits", 19 April 1996, London, published in the IEE Digest, Ref 1996/094.
    38. P A Smith, T W Button, G Dolman and C Meggs, "Performance of YBCO Thick Films in High-Q Structures", Presented at the IEE Colloquium, "Superconducting Microwave Circuits", 19 April 1996, London, published in the IEE Digest, Ref 1996/094.
    39. T W Button, P A Smith, G Dolman, C Meggs, S K Remillard, J D Hodge, S J Penn and N McN Alford, "Properties and Applications of Thick Film High Temperature Superconductors", IEEE Transactions on Microwave Theory and Techniques, Special Issue on the Microwave and Millimeter Wave Applications of High Temperature Superconductivity, 44 (1996) 1356-1360.
    40. P A Smith, T W Button, J Holmes, G Dolman, C Meggs, S K Remillard and J D Hodge, "YBCO Thick Films for High Q Resonators", Presented at the Applied Superconductivity Conference, 25-30 August 1996, Pittsburgh, USA, to be published in IEEE Transactions on Applied Superconductivity.
    41. S J Penn, N McN Alford and T W Button, "High Q Dielectric Resonators using YBa2Cu3Ox Thick Films and Polycrystalline Dielectrics", Presented at the Applied Superconductivity Conference, 25-30 August 1996, Pittsburgh, USA, to be published in IEEE Transactions on Applied Superconductivity.
    42. N Mc Alford, S J Penn and T W Button, High Temperature Superconducting Thick Films and Bulk Materials, to be published in "Functional Materials in the New Millenium: From Science to Applications", The Institute of Materials Monograph Series, 1996, in press.
    43. N Mc Alford, S J Penn and T W Button, "High Temperature Superconducting Thick Films", submitted to Supercond Sci Technol, 1996.
    44. Preparation of High Temperature Superconducting Silver-Sheathed HgBaCuO4+x Tapes, G.B. Peacock, M. Khaliq, G. Yang, T.C. Shields, I. Gameson, J.S. Abell and P.P. Edwards, Physica C 272 (1997).
    45. Comparative study of miniaturised HTS microstrip H-shaped antennas with and without enhanced capacitance. Z. Wu, D. Lacey, G. Drossos, L.E. Davis, T.W. Button, P. Smith. PHYSICA C, Vol.282, No.Pt4, pp.2511-2512 (1997)
    46. High Q dielectric resonators using YBa2Cu3Ox thick films and polycrystalline dielectrics. S.J. Penn, N.M. Alford, T.W. Button. IEEE Transactions on Applied Superconductivity, Vol.7, No.2 Pt3, pp.3500-3503 (1997)
    47. YBCO thick films for high Q resonators, P.A. Smith, T.W. Button, J. Holmes, G. Dolman, C. Meggs, S.K. Remillard, J.D. Hodge, IEEE Trans. Applied Superconductivity, Vol.7, No.2 Pt2, pp.1763-1765 (1997)
    48. HTS cavities for low phase noise oscillator applications. T.W. Button, P.A. Smith, N.M. Alford, R.B. Greed, M.J. Adams, B.F. Nicholson. IEEE Trans. Applied Superconductivity, Vol.7, No.2 Pt3, pp.3064-3066 (1997)
    49. Fabrication of high-temperature superconducting HgBa2CuO4+d within silver-sheathed tapes. G.B. Peacock, I. Gameson, P.P. Edwards, M. Khaliq, G. Yang, T.C. Shields, J.S. Abell. Physica C, Vol.273, No.3-4, pp.193-197 (1997)
    50. Microstructural characterisation of Terfenol-D crystals prepared by the Czochralski technique. Y.J. Bi, J.S. Abell. Journal of Crystal Growth, Vol.172, No.3-4, pp.440-449 (1997)
    51. Optimisation of the Properties of HTC Thick Films, T.C. Shields, T.W. Button, J. Langhorn, S.C. Watcham and J.S. Abell, IEEE Transactions on Applied Superconductivity, Vol.7, No.2 Pt2, pp.1478-1481 (1997)
    52. Study of Fault Current Limiter using YBCO Thick Film Material, D.J.Moule, P.D.Evans, T.C.Shields, S.A.L.Foulds, J.P.G.Price and J.S.Abell, IEEE Transactions on Applied Superconductivity, Vol.7, No.2 Pt1, pp.1025-1028 (1997)
    53. Processing of NdBCO thick films on YSZ substrates. T.C. Shields, A. Riley, J.S. Abell. Institute of Physics Conference Series, No.158, pp.209-212 (1997)
    54. Optimisation of the precursor powder for Bi-2223/Ag tapes. J. Jiang, J.S. Abell. Institute of Physics Conference Series, No.158, pp.953-956 (1997)
    55. Effects of precursor powder particle size on critical current density and microstructure of Bi-2223/Ag tapes. J. Jiang, J.S. Abell. Superconductor Science & Technology, Vol.10, No. 9, pp.678-685 (1997)
    56. High-temperature superconducting thick films. N.M. Alford, S.J. Penn, T.W. Button. Superconductor Science & Technology, Vol.10, No.4, pp.169-185 (1997)
    57. Influence of Microstructure on Power Dissipation in Bulk Y-Ba-Cu-O Structures, T.R. Askew, M.G. Metzler, M.S. Herron, and T.W. Button, IEEE Transactions on Applied Superconductivity, Vol.7, No.2 Pt2, pp.1600-1603 (1997)
    58. Electron-beam-induced voltage contrast and modulated optical reflectance studies of YBCO thin film resonators. S.A.L. Foulds, D.P. Almond, P. Nokrach, F. Wellhöfer, P. Woodall, J.S. Abell. Superconductor Science & Technology, Vol.11, No.4, pp.378- 382 (1998)
    59. Effects of precursor powder particle size on critical current density and microstructure of Bi-2223/Ag tapes. J. Jiang, J.S. Abell. Physica C, Vol.296, No.1-2, pp.13-20 (1998)
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    NS - Novel Superconductors
    Professor Colin Greaves and Dr Ian Gameson
     

    Over the period of the Rolling Grant programme, more than 80 papers have been published in refereed journals in the area of high temperature superconductors, with additional interests being in the synthesis of new ionic conductors and magnetic materials. A key aspect of current research interests in High-Tc compounds is the development of synthetic pathways for materials which exhibit limited stability fields, particularly those which are unstable at conventional ceramic processing temperatures. A variety of synthetic procedures have been used including hydrothermal, sol-gel, high pressure and thin film methods. In addition, thermally unstable oxide-fluoride superconductors have been successfully synthesised using a variety of chimie douce methods.

    The EPSRC Rolling Grant programme has provided firm platforms for world leading research in the areas of oxyanion and fluoride substitutions for the synthesis of new superconductors. Examples include the first suggestion that CO32- groups can be substituted into Cu-containing perovskites, the first sulphate and phosphate based cuprate superconductors and the first oxide-fluoride superconductor in which fluoride ions play a major structural role..

    Considerable experience in the most important areas (XRD, neutron diffraction, SQUID magnetometry) has been acquired and collaborations with researchers of international standing has provided additional important expertise (HREM, MASNMR, Mössbauer spectroscopy, and XPS / X-ray emission spectroscopy), which has contributed to the success of the programme.

    In the period 1994-1998, research has been focused on the synthesis of new cuprate superconductors, employing strategies founded on both cation and anion (especially oxyanion and fluoride) substitutions. 36 publications for this period are listed below. Important objectives of major High-Tc superconductivity research programmes should be the development of materials with improved performance, and demonstration of their use in real and significant applications. Although high quality synthetic programmes, such as those currently supported at Birmingham, may play a leading role towards achieving these objectives, a major re-appraisal of strategy seemed timely, and significant changes in direction are proposed under the recently funded new programme. Chemistry research at Birmingham has had an important influence on research and development worldwide, especially in the areas of oxyanion (carbonate, sulphate etc) and fluoride containing superconductors. Although interesting aspects of such materials remain unexplored, and will continue to be studied at postgraduate student level, the principal aims of this programme have been redirected towards the synthesis of totally new classes of materials. The major thrust of the continuing programme will be the synthesis of new superconductors in which the structural units linking the superconducting CuO2 layers are substantially altered relative to known compounds.

    1994-1998 Summary

    EPSRC Support for one PDRA (PR Slater; MG Francesconi from Jan 1996) was provided and research has been performed mainly in the following areas:

    The most significant advance has been the synthesis of - and demonstration of superconductivity in - a new class of materials, the copper oxide-fluorides. Establishing the structure, chemical composition and properties of Sr2CuO2F2+d has been crucial to our understanding of these materials. Subsequent work worldwide has seen the synthesis of related materials with Tc up to 111K [Physica C 257, 313 (1996)]. Subsequent work [39] has shown that removal of the excess F (d ) causes a structural transition from T (La2CuO4) to T' (Nd2CuO4). This is the first observation of such a transition merely by adjusting the anion content.

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    Publications

    1. Anion substitutions and insertions in copper oxide superconductors. M.G. Francesconi, C. Greaves. Superconductor Science & Technology, 10, No.7A, pp.A29-A37 (1997)
    2. Fluorination of the Ruddlesden-Popper type cuprates, Ln(2- x)A(1+x)Cu(2)O(6-y) (Ln = La, Nd; A = Ca, Sr). P.R. Slater, J.P. Hodges, M.G. Francesconi, C. Greaves, M. Slaski. Journal of Materials Chemistry, 7, No.10, pp.2077-2083 (1997)
    3. Substitution of SO42- anions in La1.85Sr0.15CuO4: structure and superconductivity. H.M. Palmer, C. Greaves, M. Slaski, V.A. Trofimova, Y.M. Yarmoshenko, E.Z. Kurmaev. Physica C, 291, No.1-2, pp.104-112 (1997)
    4. Fluorination of the Ruddlesden-Popper Type Cuprates, Ln2-xA1+xCu2O6-y (Ln=La,Nd; A=Ca,Sr). P.R. Slater, , J.P. Hodges, M.G. Francesconi, C. Greaves and M. Slaski. J. Mater. Chem. 7, 2077-2083 (1997).
    5. Synthesis, Structure and XPS Characterisation of the new Stoichiometric Phase Sr2CuO2F2. J.L. Kissick, C. Greaves, P.P. Edwards, V.M. Cherkashenko, E.Z. Kurmaev, S. Bartkowski and M. Neumann. Phys. Rev. B 56, 2831-2835 (1997).
    6. The Use of Fluorine for Synthesising New and Modified Superconductors. C. Greaves. Actas de la 26 Reunion Bienal de la Real Sociedad Espanola de Quimica. 715 (1997).
    7. Synthesis and structure of Bi14O20(SO4), a new bismuth oxide sulfate. M.G. Francesconi, A.L. Kirbyshire, C. Greaves, O. Richard, G. VanTendeloo. Chemistry of Materials, 10, No.2, pp.626-632 (1998)
    8. Electronic and structural effects of substituting Sr (for Ba) and Cr (for Cu) in YBa2Cu3O7-d . R.A. Jennings, C. Greaves. Superconductor Science & Technology, 11, No.3, pp.273- 277 (1998)
    9. Fluorine insertion in inorganic materials. C. Greaves, M.G. Francesconi. Current Opinion in Solid State & Materials Science, 3, No.2, pp.132-136 (1998)
    10. Superconducting Sr2-xAxCuO2F2+d (A=Ca,Ba) - Synthetic Pathways and Associated Structural Rearrangements. M.G. Francesconi, P.R. Slater, J.P. Hodges, C. Greaves, P.P.Edwards, M. Al-Mamouri and M. Slaski. J. Solid State Chem., 135, 17-27 (1998).
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    SIPS - Synthesis Of Improved Performance Superconductors
    Professor Peter P Edwards FRS, Dr Ian Gameson
     

    A major theme in this area continues to be the investigation of composition-dependent physical properties, especially in relation to the Superconductor-Insulator Transition in high temperature superconductors, and the search for new superconductors. The discovery of a new class of oxide fluoride superconductors by the Birmingham group was highlighted (Kitazawa, summary lecture, Grenoble 1994) as one of the major developments in new materials; this work led to several international patents with Merck. Professor Edwards and colleagues, in association with BICC, also holds the primary international patent on Mercury Superconductors. Dr. Ian Gameson has been a Lecturer in Inorganic Chemistry at Birmingham since April 1992. Throughout his research career he has been interested in the application of diffraction techniques to determine the structure of ordered phases. He has extensive experience in the use of X-ray and powder neutron diffraction for the determination of both the general and subtle structural features of superconducting oxides Recent work in this area includes an in-situ high pressure (8.5 GPa) neutron diffraction study of the effect of pressure on the highest Tc materials HgBa2Cu2Cu3O8+d. Features of his current synthesis work include the development of simplified routes to the preparation of large (>10g) quantities of HgBa2Cu2Cu3O8+d as well as exploring ways of inducing superconductivity, in laser ablated thin films, via post ablation synthesis.

    Recent Research Highlights

    The Birmingham group has recently completed a major review of mercurocuprates, encompassing chemistry, synthesis, crystal and electronic structure. This review is to be published as part of the NATO ASI proceedings on materials aspects of High Tc and celebrating the first decade of High Temperature Superconductivity.

    Synthesis

    We have demonstrated a reproducible, large scale synthetic route to Hg-1223 with the core prerequisites of high phase purity (>90%), with no other superconducting phases present, and large sample mass (>10g in a single batch). To achieve such results we have developed a new ?space filling? reaction vessel that both traps the volatile mercury and minimises the reaction volume.

    The availability of bulk 135K Hg-1223 has led to detailed measurements of the anisotropic magnetic penetration depth of grain-aligned Hg-1223 (with IRC, Cambridge and Clarendon, Oxford) as well as the first studies of the surface chemistry of these materials (with IRC, Cambridge).

    Structure and Characterisation

    In-situ pressure studies of Hg-1223, using powder neutron diffraction have been carried out in collaboration with the groups from Grenoble and Rutherford Appleton Laboratories. These studies reveal a dramatic shortening of the apical Cu-O bond distance, which in these compounds is anomalously large at ambient pressure. A major experimental goal, worldwide, is now to stabilise - at ambient pressure - this structural distortion which has been linked to the occurrence of the record-high Tc (164K) in Hg-1223 at high pressure.

    A joint neutron/X-ray diffraction study of HgBa2CuO4+d has revealed new insights into the local chemical structure, most notably with the observation of a displacement of the Hg ions from their ideal position upon oxygen intercalation, as the compound moves across the Semiconductor (d = 0) - to Superconductor (d ~ 0.1) Transition.

    Applications

    In collaboration with colleagues in Metallurgy and Materials Science at Birmingham, we have recently reported the fabrication of HgBa2CuO4+d within a silver-sheathed tape (Tc = 96K); this represents an important step towards the strategic goal of 135K superconducting tapes of the mercurocuprates.

    We will further investigate new routes to the bulk synthesis of higher homologues of the mercurocuprate series. Recently, a report has appeared of the synthesis of HgBa2Ca3Cu4O8+d (Hg-1234) by a conventional, rather than a high pressure route. This compound, and possibly the double layer mercury cuprate (HgO)2Ba2YCu2Oy look ideal candidates for our recently developed 'space-filling' reaction vessels (see earlier), which were so effective in the bulk synthesis of Hg1223.

    To underpin our proposed studies of mercurocuprates in wire and tape form, we are investigating with colleagues from Metallurgy and Materials Science, grain-growth, morphology and texturing both sealed tube and open synthesis conditions.

    By varying the control parameters of firing temperature, duration, and cycling/ quenching procedures - found recently to be particularly effective in grain growth and the enhancement of superconducting volumes within tapes - we are working on the optimization of the texturing of this 135K superconductor. Preliminary results are particularly encouraging, and highlight the very great potential for our studies.

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    Publications 1994-1998 (I. Gameson and P.P. Edwards)

      Book: "The Metal-Nonmetal Transition Revisited" P.P. Edwards and C.N.R. Rao, F.R.S., eds., (Taylor and Francis, London) (1995)
         
      Journals:
         
    1. "A Study of the Orientation Dependence of the 63Cu Nuclear Magnetic Resonance in the (Tl0.5Pb0.5)Sr2(Ca1-yYy)Cu2O7-d System", G.P. Dai, D.P. Tunstall, R.S. Liu and P.P. Edwards, Physica C 220, 93-100, (1994).
    2. "Structure of the Li1+xTi2-xO4 Superconducting System: A - Neutron Diffraction Study", M. Dalton, I. Gameson, A.R. Armstrong and P.P. Edwards, Physica C 221, 149-156, (1994).
    3. "The Continued Absence of EPR at High Temperatures in Ln2Cu1-xZnxO4 (Ln = La, Nd)",R. Janes and P.P. Edwards, J. Phys. Condens. Matter, 6, L315-L318, (1994).
    1. "Synthesis and Superconducting Properties of the Strontium Copper Oxyfluoride Sr2CuO2F2+d", M. Al-Mamouri, P.P. Edwards, C. Greaves and M. Slaski, Nature, 369, 382-384 (1994).
    2. "63Cu NMR Shift and Relaxation Behaviour in Tl2Ba2Ca2Cu3O10-d", Z.P. Han, R. Dupree, R.S. Liu and P.P. Edwards, Physica C 226, 106-112 (1994).
    3. "The Hg-Bearing Cuprate Superconductors: The Relationship Between the Oxygen Content and Tc in Hg-1212 and the Effect of Pressure on the Structure and Tc in Hg-1223", M. Marezio, J.J. Capponi, P.G. Radaelli, P.P. Edwards, A.R. Armstrong and W.I.F. David, Eur. J. Solid State Inorg. Chem., t.31, 843-854, (1994).
    4. "Titanium Nuclear Magnetic Resonance in Metallic Superconducting Lithium Titanate and its Lithium-Substituted Derivatives Li1+xTi2-xO4 (0<x<0.10)", D.P. Tunstall, J.R.M. Todd, S. Arumugam, G. Dai, M. Dalton and P.P. Edwards, Physical Review B, 50, No. 22, 16541-16549 (1994).
    5. "A 7Li NMR Study of the Superconducting Spinel Li1+xTi2-xO4", M. Dalton, D.P. Tunstall, J. Todd, S. Arumugam and P.P. Edwards,, J. Phys. Condens. Matter, 6, 8859-8870 (1994)
    6. "Copper NMR Studies of the Nd2CuO4-xFx System", G.P.Dai, B. Ctortecka, D.P. Tunstall, M. Jones, I. Gameson and P.P. Edwards, Solid State Comm., 91, No. 3, 205-208 (1994).
    7. "Chemical Design and Synthesis of Oxy-Anion and Oxy-Fluoride Cuprate Superconductors", C. Greaves, M. Al-Mamouri, P.R. Slater, P.P. Edwards. Physica C, 235-240, 158-161 (1994).
    8. "Synthesis and Characterisation of Laser Ablated YBa2-xSrxCu3O7 Thin Films", C. Greaves, P.R. Slater, A. Asab, P. Shaffery, I. Gameson, P.P. Edwards, S.Sutton, F. Wellhofer, P. Woodall, Physica C, 235-240, 701 (1994).
    9. "Issues Involved in the Synthesis of Mercury Containing Superconductors" G.B. Peacock, A. Asab, J.P. Hodges, I. Gameson, P.P. Edwards. Physica C, 235-240, 911 (1994).
    10. "Asymmetry of the Apical-Oxygen Vibration Raman Lineshape in the Tl Based 1212 System", T. Mertelj, P. Mihailovic, R.S. Liu, J.R. Cooper, I. Gameson, P.P. Edwards, Physica C, 235-240, 1141 (1994).
    11. "Charge Distribution in (Tl,Pb)Sr2Ca2Cu3O9-d (Tc = 124K): A 17O NMR Study", Z.P. Han, R. Dupree, A.P. Howes, R.S. Liu and P.P. Edwards, Physica C, 235-240, 1709-1710 (1994).
    12. "NMR Studies in the Superconducting Spinel System Li1+xTi2-xO4", M. Dalton, D.P. Tunstall, J. Todd, S. Arumugum, P.P. Edwards, Physica C, 235-240, 1729-1730 (1994).
      1995:
         
    1. "Superconductivity up to 64K in the Copper Oxyfluorides Sr2-xAxCuO2F2+d (A = Ca, Ba) Prepared Using NH4F as a Fluorinating Reagent ", P.R. Slater, P.P. Edwards, C. Greaves, I. Gameson, M.G. Francesconi, J.P. Hodges, M. Al-Mamouri, M. Slaski, Physica C, 241, 151 (1995).
    2. "Further Measurements on the Tl0.5Pb0.5Sr2(Ca1-yYy)Cu2O7-d System Pb NMR and Magnetic Susceptibility" G.P. Dai, D.P. Tunstall, M. Dalton, R.S. Liu and P.P. Edwards, Physica C, 244 207-213 (1995).
    3. "The Metal-Nonmetal Transition: The Continued/Unreasonable Effectiveness of Simple Criteria at the Transition", P.P. Edwards in Perspectives in Solid State Chemistry, ed. K.J. Rao, Narosa Publishing House, New Delhi, 1995, p.250-271.
    4. "The Metal-Nonmetal Transition: A Global Perspective" P.P. Edwards, T.V. Ramakrishnan and C.N.R. Rao, J. Phys. Chem., 99, 5228-5239 (1995).
    5. "Synthesis and Structure of Sr2VN3and Ba2VN3, Two New Nitrodovanadates", D.H. Gregory, M.G. Barker, P.P. Edwards and D.J. Siddons, Inorg. Chem., 34, 3912-3916 (1995).
    6. "Synthesis and Structure of Ca6MnN5: A New Nitromanganate with Planar [MnN3]6- Anions", D.H. Gregory, M.G. Barker, P.P. Edwards, and D.J. Siddons, Inorg. Chem., 34, 5195-5198 (1995).
    7. "An Improved Route to the Synthesis of Superconducting Copper Oxyfluorides Sr2-x AxCuO2F2+d (A = Ca, Ba) using Transition Metal Difluorinating Agents", P.R. Slater, J.P. Hodges, M.G. Francesconi, P.P. Edwards, C. Greaves, I. Gameson and M. Slaski, Physica C, 253 16-22 (1995).
    8. "Single-Step Synthesis and Crystal Structure of HgBa2CuO4+d with a Tc of 97K", A. Asab, A.R. Armstrong, I. Gameson and P.P. Edwards, Physica C, 255, 180-187 (1995).
    9. "Effective Synthesis of HgBa2Ca2Cu3O8+y: The Highest Tc Superconductor, G.B. Peacock, I. Gameson, M. Slaski, W. Zhou, J.R. ooper and P.P. Edwards, Adv. Mat., 7 No. 11, 925-927, (1995).
    10. "Synthesis and Structure of the Calcium Copper Oxyfluoride, Ca2CuO2F2+d, M. Al-Mamouri, P.P. Edwards, C. Greaves, P.R. Slater and M. Slaski, J. Mater. Chem., 5(6), 913-916 (1995).
    11. "The Surface Chemistry of HgBa2CuO4+d. An Investigation by High-Resolution Electron Microscopy" W. Zhou, A. Asab, I. Gameson, D.A. Jefferson and P.P. Edwards. Physica C, 248, 1-10 (1995)
    12. "Further Copper NMR Studies of the Electron Superconductor Nd2CuO3.7F0.3", G.P. Dai, D.P. Tunstall, P.P. Edwards and M.O. Jones, Solid State Comm., 93, No. 12, 989-993 (1995).
      1.  
      1996:
         
    13. "Crystal Structure of HgBa2Ca2Cu3O8+d at High Pressure (to 8.5 GPa) Determined by Powder Neutron Diffraction", A.R. Armstrong, W.I.F. David, I. Gameson, P.P. Edwards, J.J. Capponi, P. Bordet, M. Marezio, Phys. Rev. B., 52, No. 21, 15551-15557 (1996).
    14. "Observation of Superconductivity (Tc = 50K) in a New Tetragonal Alkaline-Earth Cuprate Sr0.8Ba1.2CuO3+d, Synthesised at Ambient Pressure", J.P. Hodges, P.R. Slater, P.P. Edwards, C. Greaves, M. Slaski, G. Van Tendeloo, S. Amelinckx, Physica C, 260, 249-256, (1996).
    15. "Synthesis and Structure of Two New Layered Ternary Nitrides, SrZrN2 and SrHfN2", D.H. Gregory, M.G. Barker, P.P. Edwards and D.J. Siddons, Inorganic Chem., 35, 7608-7613, (1996)
    16. "Synthesis and Crystal Structures of the New Ternary Nitrides Sr3CrN3 and Ba3CrN3", M.G. Barker, M.J. Begley, P.P. Edwards, D.H. Gregory, S.E. Smith, J. Chem. Soc. Dalton Trans., 1, 1-5, (1996)
    17. "X-Ray Emission and Photoelectron Spectra, and the Location of Fluorine Atoms in Strontium and Calcium Copper Oxyfluorides", E.Z. Kurmaev, L.V. Elokhina, V.V. Fedorenko, S. Bartkowski,, M. Neumann, C. Greaves, P.P. Edwards, P.R. Slater, M.G. Francesconi, J. Phys. Cond. Matter, 8, 4874-4854, (1996).
    18. Anisotropic Magnetism Penetration Depth of Grain-Aligned: HgBa2Ca2Cu3O8+d, C. Panagopoulos, J.R. Cooper, G.B. Peacock, I. Gameson, P.P. Edwards, W. Schmidbauer and J.W. Hodby, Phys. Rev. B., 53, R2999-3002, (1996).
    19. "Induction of Superconductivity in Pulsed Laser Ablated La2CuO4 Thin Films by Post-Deposition Fluorination", S.T. Lees, I. Gameson, M.O. Jones, P.P. Edwards, C. Greaves, F. Wellhofer, P. Woodall, I. Langford and M. Slaski, Physica C, 270, 305-310, (1996).
      1997:
    1. "Fabrication of High Temperature Superconducting HgBa2CuO4+d Within Silver-Sheathed Tapes", G.P. Peacock, I. Gameson, P.P. Edwards, M. Khaliq, G. Yang, T.C. Shields, J.S. Abell, Physica C, 273, 193-197 (1997)
    2. "Probing the Order Parameter and the c-axis Coupling of High Tc Cuprates by Penetration Depth Measurements", C. Panagopoulos, J.R. Cooper, T. Xiang, G.B. Peacock, I. Gameson and P.P. Edwards, Phys. Rev. Letts., in press.
    3. "Bulk Synthesis of the 135K Superconductor HgBa2Ca2Cu3O8+d", G.B. Peacock, I. Gameson and P.P. Edwards, Advanced Materials, in press.
    4. The normal state gap in 1 and 2 layer cuprates. R. Michalak, R. Dupree, A. Asab, I. Gameson, P.P. Edwards. Physica B, Vol.230, pp.822-824 (1997)
    5. Synthesis, structure, and properties of the high-temperature superconductor HgBa2CuO4+d . J.P. Hedges, I. Gameson, P.P. Edwards, A.P. Kharel, A. Porch. Physical Review B-Condensed Matter, Vol.55, No.18, pp.12776-12783 (1997)
    6. Synthesis, structure, and XPS characterisation of the stoichiometric phase Sr2CuO2F2. J.L. Kissick, C. Greaves, P.P. Edwards, V.M. Cherkashenko, E.Z. Kurmaev, S. Bartkowski, M. Neumann. Physical Review B-Condensed Matter, Vol.56, No.5, pp.2831- 2835 (1997)
    7. Induction of high-temperature superconductivity in pulsed laser ablated La2CuO4 thin films by room temperature chemical oxidation. S.T. Lees, P.P. Edwards, I. Gameson, M.O. Jones, M. Slaski, C. Rial, U. Amador, E. Moran. Advanced Materials, Vol.9, No.10, p.823 (1997)
    8. Probing the order parameter and the c-axis coupling of high-T-c cuprates by penetration depth measurements. C. Panagopoulos, J.R. Cooper, T. Xiang, G.B. Peacock, I. Gameson, P.P. Edwards. Physical Review Letters, Vol.79, No.12, pp.2320-2323 (1997)
    9. Anisotropic penetration depth measurements of high-T-c superconductors. C. Panagopoulos, J.R. Cooper, T. Xiang, G.B. Peacock, I. Gameson, P.P. Edwards, W. Schmidbauer, J.W. Hodby, Physica C, Vol.282, No.Pt1, pp.145-148 (1997)
    10. The surface chemistry of Hg-containing superconductors by HREM. W. Zhou, C. Panagopoulos, E.T.C. Lee, J.P. Hodges, G.B. Peacock, A. Asab, I. Gameson, P.P. Edwards. Physica C, Vol.282, No.Pt2, pp.909-910 (1997)
    11. Fluorination of mercury-based high-temperature superconductors. G.B. Peacock, I. Gameson, M. Slaski, J.J. Capponi, P.P. Edwards. Physica C, Vol.289, No.3-4, pp.153-160 (1997)
    12. Bulk synthesis of the 135 K superconductor HgBa2Ca2Cu3O8+d . G.B. Peacock, I. Gameson, P.P. Edwards. Advanced Materials, Vol.9, No.3, p.248 (1997)
    13. Mott insulator high T-c bipolaronic superconductor transition in cuprates - Discussion. P.P. Edwards,
    14. 1998:

    15. The effect of nitrates on thallium based oxycarbonate superconductors. M.O. Jones, I. Gameson, P.P. Edwards, B. Raveau. Journal of Superconductivity, Vol.11, No.1, pp.123-124 (1998)
    16. The mechanism of surface decomposition of Tl- and Hg-containing superconductors. W. Zhou, D.A. Jefferson, W.Y. Liang, G.B. Peacock, A. Asab, I. Gameson, P.P. Edwards. Journal of Superconductivity, Vol.11, No.1, pp.13-14 (1998)
    17. Fluorination of underdoped mercurocuprate superconductors. G.B. Peacock, A. Fletcher, M. Slaski, I. Gameson, J.J. Capponi, P.P. Edwards. Journal of Superconductivity, Vol.11, No.1, pp.127-128 (1998)
    18. Synthesis and structure of Hg1-xCrxSr2CuO4+d mercurocuprates. N.C. Hyatt, M.O. Jones, I. Gameson, M. Slaski, G.B. Peacock, J.A. Hriljac, P.P. Edwards. Journal of Superconductivity, Vol.11, No.1, pp.141-142 (1998)
    19. The insulator-superconductor transformation in cuprates. P.P. Edwards, N.F. Mott, A.S. Alexandrov. Journal of Superconductivity, Vol.11, No.1, pp.151-154 (1998)
    20. Superconducting Sr(2-x)A(x)CuO(2)F(2+d ) (A = Ca, Ba): Synthetic pathways and associated structural rearrangements. M.G. Francesconi, P.R. Slater, J.P. Hodges, C. Greaves, P.P. Edwards, M. AlMamouri, M. Slaski. Journal of Solid State Chemistry, Vol.135, No.1, pp.17-27 (1998)
    21. Synthesis and superconductivity of highly underdoped HgBa2CuO4+d . G.B. Peacock, A. Fletcher, I. Gameson, P.P. Edwards. Physica C, Vol.301, No.1-2, pp.1-8 (1998)
    Return to Contents 
     Microwave Properties, Device and Antenna Applications
    Dr Adrian Porch, Dr Mike Lancaster, Dr Fred Huang and Professor Colin Gough
     

    This has been a collaborative programme involving the Schools of Electronic and Electrical Engineering (Dr A Porch and Dr M J Lancaster) and Physics and Astronomy (Prof C E Gough). The programme underpins a wide range of application programmes on HTS microwave devices, antennas and systems supported by additional grants from the EC, EPSRC, DRA, DTI and UK industry. State of the art microwave facilities include three vector network analysers, covering the range 45 MHz - 50 GHz, microwave modelling software (both commercial and in-house software packages), and a number of cryostats allowing measurements to be performed down to 1.2 K in dc applied magnetic fields up to 12 T.

    The Group have contributed significantly to the worldwide understanding of the high frequency science of HTS materials and have also developed a number of innovative microwave devices [1,2]. Recent work (1994 - present) has included the development of a novel coplanar resonator technique [3] for evaluating absolute values of the microwave surface impedance of a variety of HTS thin films between 5 -20 GHz, with a quantitative modelling of the microwave current distributions. This technique offers unparalleled sensitivity for measuring the microwave properties and has the added advantage that coplanar resonators can be basic building blocks for numerous HTS microwave devices. In addition, the antenna work has produces a demonstration of the worlds first HTS superdirectional antenna array in both wire and a 16 element planar thick film circuit. Although not supported in the rolling grant for more than 2 years, this work is now continuing in a separate grant demonstrating new superconducting antenna arrays [22, 33, 46, 59]. The coplanar resonator technique has been used to investigate films deposited by a variety of techniques (Birmingham, DRA and collaborators within the ESPRIT Supermica programme), which has led to optimisation of film growth and processing for highest microwave performance [4-9]. From these studies, we conclude that all deposition techniques are capable of producing very low surface resistance films with good power handling properties, and that that finite losses at low temperatures and the inductive response is consistent with d-wave pairing. These fundamental studies have aided the design, development and demonstration of a number of microwave devices, including miniature adaptive filter banks [1,10,11] and novel delay line resonators and filters [1,12-14]. Measurements in applied static magnetic fields [15-18] have allowed the study of the pinning and damping of flux lines/pancakes in YBCO and GBCO thin films, and 2212-BSSCO, GBCO and YBCO single crystals, where new physics is emerging in the superclean (wct >1) limit (M. Golosovsky et al., Superconductor Science and Technology, 9 1 (1996)). Because losses in parallel fields are low, we have been able to develop an ultra-high sensitivity ESR system [19] based on a HTS coplanar resonator (patent), which has already achieved a performance comparable to the best commercial system. Studies of the flux line response of high quality, small HTS crystals have been made for the first time using a highly-sensitive hollow dielectric resonator [17], free of superconducting materials, so that uniquely we can make high sensitivity measurements over a wide field range. Single crystal measurements are in general agreement with thin film results, except at low temperatures where a linear rather than T2 dependence is observed in the magnetic penetration depth in single crystals. Interestingly, there appears to be fundamental difference between YBCO and 2212-BSCCO with low temperature B-dependences proportional to B and ~B1/2 respectively.

    The group has published well over 100 papers since the start of the rolling grant; over half of these are journal publications, together with three patent applications. Dr Lancaster has recently written a book entitled Passive Microwave Device Applications of High Temperature Superconductors (Cambridge University Press), with 340 pages, 162 figures and 666 references. Over two thirds of the book is based on microwave filters and antennas, the other third is on the physics of superconductors at microwave frequencies. Dr Lancaster is regularly invited to international conferences in order to discuss the work at Birmingham. For example, this year Dr Lancaster has accepted invitations to speak at the International Conference on Microwave and Millimetre Wave Technology in Beijing and the International Symposium on Microwaves and Sub-Millimetre Waves in Kharkov. In June he will be talking at a workshop organised by the US Defence Advanced Research Projects Agency (DARPA); the purpose of which is to give DARPA ideas on future research initiative for HTS in telecommunications. In addition, the group has published invited articles on their HTS work in a number of journals, including a special edition of the IEEE Transactions of Microwave Theory and Techniques. Dr Lancaster has recently been appointed to the IEEE Microwave Theory and Techniques Society International Microwave Symposium technical committee. This is the technical committee looking at superconducting technology for the IEEE MTT-S. Professor Colin Gough played a leading role in setting up the ESPRIT- funded SCENET (European Networks of Excellence in Superconductivity involving ~80 nodes across Europe) and organised an EC Workshop on Materials for Electronic Devices in Rome (January 1998): he has also coordinated and written an agreed European Roadmap for Superconducting Electronics, covering all aspects of superconducting device applications.

    Recently the group in Electrical and Electronic Engineering was awarded a European contract with a number of industrial companies in order to develop HTS systems for mobile communications. The contract, with acronym SUCOMS resulted directly from experience gained in the rolling grand and our other EPSRC device grant. The contract participants are GEC-Marconi, Thomson CSF, Leybold, Wuppertal University and ourselves. The objective is to produce an HTS subsystem for a DCS1800 mobile communications base station. The first system will be trialed in summer 1998 with the French Telecom operator SFR, and also at Expo?98 in Lisbon by the Portuguese operator TMN. At a later date, it will also be trialed in Singapore by SIGTEL. The role of the University of Birmingham is the design of the receive filters, obviously the centrepiece of the system. The filter has now been completed and works well.

    Return to Contents

    Publications from 1994 to 1998

    1. J.R.Powell, A.Porch, R.G.Humphreys, F.Wellhofer, M.J.Lancaster, C.E.Gough, "Field, temperature, and frequency dependence of the surface impedance of YBa2Cu3O7 thin films". Physical Review B-Condensed Matter, Vol.57, No.9, pp.5474- 5484 (1998)
    2. J.S. Hong, M.J. Lancaster, "Cross-coupled microstrip hairpin-resonator filters". IEEE Transactions On Microwave Theory And Techniques, Vol.46, No.1, pp.118-122 (1998)
    3. Yeo K. S. K. and Lancaster M. J. "Variable superconducting ferrite phase shifter" 4th International student seminar on high temperature superconductors at microwave frequencies. May 19-25 1997 Wuppertal University, Germany 1997-09-22
    4. Hong J.-S., Lancaster M. J., Jedamzik D., and Greed R. B., "8-pole superconducting quasi-elliptic function filter for mobile communications application" IEEE MTT-S International Microwave Symposium, Baltimore, USA June 1998
    5. H.Y. Wang, J.S. Hong, M.J. Lancaster, "Aperture coupled high-temperature superconductor microstrip small antennas". Institute of Physics Conference Series, No.158, pp.359-362 (1997)
    6. J.S. Hong, M.J. Lancaster. "Theory and experiment of novel microstrip slow-wave open-loop resonator filters". IEEE Transactions on Microwave Theory And Techniques, Vol.45, No.12 Pt2, pp.2358-2365 (1997)
    7. C. Fraser, M.J. Lancaster, "Microwave filtering realized through incoherent optical processing". IEEE Microwave and Guided Wave Letters, Vol.7, No.8, pp.225-226 (1997)
    8. H.C.H.Cheung, M.Holroyd, F.Huang, M.J.Lancaster, B.Aschermann, M.Getta, G.Muller, H.Schlick, "125% bandwidth superconducting chirp filters". IEEE Trans. Applied Superconductivity, Vol.7, No.2 Pt3, pp.2359-2362 (1997)
    9. J.S.Hong, M.J.Lancaster, "Investigation of microstrip pseudo-interdigital bandpass filters using a full-wave electromagnetic simulator". International Journal Of Microwave And Millimeter-Wave Computer- Aided Engineering, Vol.7, No.3, pp.231-240 (1997)
    10. J.R. Waldram, P. Theopistou, A. Porch, H.M. Cheah, "Two-fluid interpretation of the microwave conductivity of YBa2Cu3O7-d ". Physical Review B-Condensed Matter, Vol.55, No.5, pp.3222- 3229 (1997)
    11. Z.Wu, D.Lacey, G.Drossos, L.E.Davis, T.W.Button, P.Smith, "Comparative study of miniaturised HTS microstrip H-shaped antennas with and without enhanced capacitance". Physica C, Vol.282, No.Pt4, pp.2511-2512 (1997)
    12. S.J.Penn, N.M.Alford, T.W.Button. "High Q dielectric resonators using YBa2Cu3Ox thick films and polycrystalline dielectrics", IEEE Trans. Applied Superconductivity, Vol.7, No.2 Pt3, pp.3500-3503 (1997)
    13. T.W.Button, P.A.Smith, N.M.Alford, R.B.Greed, M.J.Adams, B.F.Nicholson. "HTS cavities for low phase noise oscillator applications". IEEE Trans. Applied Superconductivity, Vol.7, No.2 Pt3, pp.3064-3066 (1997)
    14. P.A.Smith, T.W.Button, J.Holmes, G.Dolman, C.Meggs, S.K.Remillard, J.D.Hodge, "YBCO thick films for high Q resonators". IEEE Transactions On Applied Superconductivity, Vol.7, No.2 Pt2, pp.1763-1765 (1997)
    15. J.R.Powell, A.Porch, M.J.Lancaster, R.G.0Humphreys, C.E.Gough, "Hysteretic microwave measurements of YBCO thin films in small swept applied fields". Institute of Physics Conference Series, No.158, pp.125-128 (1997)
    16. H.Li, W.X.Zhu, J.H.Cai, P.S.Zhang, Y.Zhou, A.S.He, Z.L.Gong, T.S.He, P.A.Smith, T.W.Button, J.E.Holmes, M.J.Lancaster, A.Porch, B.Avenhaus, P.Woodall, F.Wellhofer, C.E.Gough, G.Kaiser, P.Seidel, M.Thurk, "Demonstration of HTS microwave sub-systems with a pulse tube cryocooler". Physica C, Vol.282, No.Pt4, pp.2527-2528 (1997)
    17. J.J.Wingfield, J.R.Powell, A.Porch, C.E.Gough, "Field-dependent surface impedance of YBCO single crystals and evidence for a nonzero Hall term". Physica C, Vol.282, No.Pt3, pp.1597-1598 (1997)
    18. C.E.Gough, A.Porch, M.J.Lancaster, J.R.Powell, B.Avenhaus, J.J.Wingfield, D.Hung, R.G.Humphreys, "High Tc coplanar resonators for microwave applications and scientific studies". Physica C, Vol.282, No.Pt1, pp.395-398 (1997)
    19. A. Porch and C. E. Gough, "Microwave applications of HTS", Current Opinion in Solid State and Materials Science, Vol.2, No.1, pp.11-17 (1997) - Invited Review Article.
    20. Lancaster M. J. "Passive microwave device applications of high temperature superconductors" Cambridge University Press, Cambridge UK 1997.
    21. Hong Li, Wenxiou Zhu, Jinghui Cai, Pingsheng Zhang, Yuan Zhou, Aisheng He, Zhonglin Gong, Yusheng He, Smith P., Button T., Alford NMcN., Lancaster M. J., Porch A., Avenhaus B., Woodall P., Wellhofer F., Gough C. E., Kaiser G., Seidel P., and Thurk M. "A demonstration of the HTS microwave sub-system with pulse tube cooler" Physica C 282-287 pp 2527-2528 1997
    22. Esa M., and Lancaster M. J. "Antena Tercetak Mengalir Lampau Model Kecil Untuk Kegunann Terhad-Ruang" Jurnal Technology UTM V26 June 1997 (In Malysian) pp75-81
    23. Lancaster M. J. and Hong J. S. "Microstrip filters using small resonent components" IEE Colloquium on Microwave components for communication systems 23rd April 1997 University of Bradford.
    24. Hong J. S. and Lancaster M. J., "Investigation of Microstrip Pseudo-Interdigital bandpass filters using full-wave electromagnetic simulator" International Journal of Microwave and millimeterwave computer aided Engineering V7 1997 pp 231-240
    25. Cheung H. C. H., Holroyd M., Hung F., Lancaster M. J., Aschermann B., Getta M., Muller G., Schlick H. "125% Bandwidth Superconducting Chirp Filters" IEEE Trans. on Applied Superconductivity, V7(2) pp 2359-2362
    26. J.J.Wingfield, J.R.Powell, C.E.Gough, A.Porch, "Sensitive measurement of the surface impedance of superconducting single crystals using a sapphire dielectric resonator". IEEE Trans. Applied Superconductivity, Vol.7, No.2 Pt2, pp.2009-2012 (1997)
    27. M. J. Lancaster, J.-S. Hong H. J. Chaloupka, D. Jedamzik, R. B. Greed, G Auger, Y Vourc?h, J. C. Mage "Superconducting Filters for Mobile Communication Base Stations" Acts Mobile Summit, Aalbourg Denmark September 1996
    28. Hong J. S. and Lancaster M. J. "Recent advances in microstrip filters for communications and other applications" IEE Colloquium on Advances in Passive Microwave Components. May 1997 IEE London
    29. Hong J. S. and Lancaster M. J. "Experimental investigation of aperature coupled four-element microstrip H-shaped antenna for multi-function oprtation. 10th International Conference on Antennas and Propagation 14-17 April 1997, IEE Conference puplication numner 436 pp 1.78-1.81
    30. M. J. Lancaster et al., "Miniature superconducting filters", IEEE Trans. MTT 44 1339 (1996)
    31. J. S. Hong et al., "End-coupled microstrip slow wave resonator filter", Electronics Lett., 32 1494 (1996)
    32. J. S. Hong et al., "Couplings of microstrip square open-loop resonators for cross-coupled planar microwave filters", IEEE Trans. MTT, 44 2099 (1996)
    33. T. W. Button et al., "Properties and applications of thick film HTS", IEEE Trans. MTT, 7 1356 (1996)
    34. J. R. Powell et al., "Microwave surface impedance of YBCO thin films in dc applied fields", Czech. J. Phys., 46 1089 (1996)
    35. J. J. Wingfield et al, "Dielectric resonator measurements of Zs on HTS crystals in high dc magnetic fields", Czech. J. Phys., 46 1087 (1996)
    36. Powell J. R., Porch A., Wellhofer F., Darlington C. N., Lancaster M. J., Bollmeier T., and Stritzker B. "Laser ablated ferroelectric and superconducting thin films for microwave applications" IEE Colloquium on the Microwave Applications of Superconductors April 19th 1996
    37. Hong J. S. and Lancaster M. J. "Compact microwave elliptic function filters using novel meander open-loop resonators" Electronics Letters V32(6) pp 563-564 1996
    38. Hong J.-S. and Lancaster M. J. "Couplings of Microstrip Square Open-Loop Resonators for Cross-Coupled Planar Microwave Filters" IEEE Transactions on Microwave Theory and Techniques MTT44(12) pp 2099-2109 November 1996
    39. Hong J. S. "Novel slow-wave ladder microstrip lines and filters" European Microwave Conference 1996 pp431-434
    40. Hong J. S. and Lancaster M. J. "Microstrip H-shaped antenna aperature coupled to a microstrip feedline" 26th European Microwave Conference pp284-287
    41. J. S. Hong et al., "New HTS microstrip lines and resonators", Institute of Physics Conference Series, Vol. 148 1195 (1995)
    42. M. Esa and M.J. Lancaster, "Electrically small high-temperature superconducting symetrical meander dipole antenna" European Conference on Applied Superconductivity Edinburgh UK, 1995.
    43. A. Porch et al., "The coplanar resonator technique for determining the surface impedance of YBCO thin films", IEEE Trans. MTT 43 306 (1995)
    44. B. Avenhaus et al., "Microwave properties of YBCO thin films", IEEE Trans. Applied Superconductivity, 5 1737 (1995)
    45. Porch A, Powell J.R., Lancaster M.J., Edwards J.A. and Humphreys R.G., "Microwave conductivity of patterned YBCO thin films", IEEE Trans. Applied Superconductivity, 5 1987 (1995)
    46. S. Hensen et al., "Optimisation of the microwave properties of high oxygen-sputtered YBCO and YbBCO films", Institute of Physics Conference Series, Vol. 148 1127 (1995)
    47. A. Porch et al., "Surface impedance of YBCO thin films on LaAlO3 and NdGaO3 substrates deposited by MOCVD", Institute of Physics Conference Series, Vol.148 1043 (1995)
    48. B. Avenhaus et al., "Switched YBCO lumped element bandstop filter", Electronics Lett., 31 985 (1995)
    49. J. R. Powell et al., "Microwave surface impedance of YBCO thin films in dc applied magnetic fields", Institute of Physics Conference Series, Vol. 148 1119 (1995)
    50. J. J. Wingfield et al., "Ultra-sensitive ESR system based on a HTC coplanar resonator", Institute of Physics Conference Series, Vol. 148 1215 (1995)
    51. A. Porch et al., "Microwave surface impedance of unpatterned and patterned YBCO thin films produced by pulsed laser deposition", Institute of Physics Conference Series, Vol. 148 1039 (1995)
    52. Hong J. S. and Lancaster M. J. "A novel microwave periodic structure - The ladder microstrip line." Microwave and Optical Technology Letters V9(4) pp 207-210 1995
    53. Hong J. S. and Lancaster M. J. "Bandpass characteristics of new dual-mode microstrip square loop resonators." Electronics Letters V31(11) pp 891-892 1995
    54. Ivrissimtzis L. P., Lancaster M. J., and Alford N. McN, "A supergain YBCO Antenna Array with integrated Feed and Balun" IEEE Trans. on Applied Superconductivity V5(2) pp 3199-3202 1995
    55. Yeadon M., Aindow M., Welhofer F., Abell J. S., Avenhaus B., Woodall P., Porch A., Lancaster M. J. "Microstructural and Microwave properties of Thick Epitaxial films of YBa2Cu3O7-d " IEEE Trans. on Applied Superconductivity V5(2) pp 1214-1217 1995
    56. Cheung H. C. H., Huang F., Lancaster M. J. Humphreys R. G. and Chew N. G. "Improvements in superconducting Linear phase microwave delay line bandpass filters" IEEE Trans. on Applied Superconductivity V5(2) pp 2675-2677 1995
    57. Hong J. S., and Lancaster M. J. "Development of new microstrip pseudo-interdigital bandpass filters" IEEE Microwave and Guided Wave Letters V5(8) pp 261-263 1995
    58. Hong J. S. and Lancaster M. J. "Pseudo-interdigital bandpass filter" British Patent Application No. 9515977.8 Aug. 1995.
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    92. Powell J.R., Porch A., Gough C.E. and Humphreys R.G., `Magnetic field dependence of the microwave surface impedance of YBCO thin films', Presented at CMMP 94, Leeds, 19-21 December, 1994
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