Influence of Local Structure on Superconducting Properties of Samples in YBaCuO and Related Systems

HTSC - 6885

Work Area: High-Tc Superconductivity

Keywords high Tc superconductivity

Start Date: 1 July 92 / Duration: 24 months / Status: running

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Abstract HTSC aims to determine the local structure of samples of high Tc superconductors. The aim is the establishment of meaningful relationships between the local structure, the synthesis procedures, and the fundamental physical properties. The ultimate goal will be to attain control of the local structure and to produce samples with a given local structure, which will allow meaningful physical measurements. The emphasis will be on the identification of flux pinning centres.

Aims

The scientific goal of the Working Group is the determination of the local structure of Cu oxide high Tc superconductors. Samples of Cu oxide superconductors contain superstructures, microwins, non stoichiometry in the anion sublattice, cation ordering, point and extended defects, and intergrowth.With such samples, if we limit ourselves to Bragg scattering, we can only determine the average structure. In order to approximate the local arrangement we are: (i) using more than one radiation (X-ray, neutrons, electrons); (ii) taking into account the diffuse scattering; (iii) carrying out high resolution electron microscopy; (iv) using absorption techniques (EXAFS and XANES).

Activities

Within the framework of the WG two workshops have been organised, the first at El Escorial (Spain) on 16-17 October 1992 and the second at Port Hydra (Greece) on 7-8 May 1993. The WG laboratories have access, via collaborations with Darmstadt and Ris_, to the large installations of a synchroton light source (Hasylab) and neutron scattering facility (Ris_). A round table about the future of the WG was held at the end of the meeting.

At Port Hydra the workshop comprised ten lectures given by members of the WG laboratories and eighteen posters. Dr. A. Bianconi (University of Rome) spoke about the problems of the local structure in Bi2Sr2CaCu2O8+x. Dr. D. Jefferson (Cambridge University) illustrated the microstructural irregularities in various oxide superconductors, and Dr. J.P. Locquet (IBM Zürich) spoke about a new growth mechanism of thin films of high Tc superconductors.

Progress and Results

Some of the most important contributions made by the Working Group are:

• The synthesis of new Cu oxide superconductors obtained by replacing, in known Cu-oxide compounds, Cu polyhedra by anionic groupings, such as CO3-2, SO4-2, NO3-1, BO3-3. For example, (Y1.6CA0.4)2Ba4Cu5(CO3,NO3)O11 and TISr4-xBaxCu2CO3O7 (1The synthesis of a new Hg-bearing Cu oxide compound, HgBa2CuO4+d, which was found to become superconducting at 94 K. This proved to be the first member of a new homologous series of high Tc superconductors, HgBa2Ca1-nCunO2n+2+d , where a record Tc (134 K) was found for the third member (ETH-Zürich).
• The study of the microstructure of YBa2(Cu1-xC0x)3O7-d and its correlation with the superconductivity properties. It has been shown that the twin planes in superconductivity YBCO samples act as pathways for magnetic flux creep rather than as pinning centers. Inter-grain flux percolates along the twin walls into the superconducting grains and inter-grain critical current density is reduced by intra-grain mesostructural properties.
• The study of the phase diagram of YBa2Cu306+X for 0.85

  Potential

  The new oxide high Tc superconductors obtained by replacing Cu polyhedra by CO3-2, SO4-2, NO3-1 and BO3-3 groupings open up the possibility of changing the distances between the CuO2 superconducting layers on an ad hoc basis. The replaced Cu polyhedra are those which do not participate directly in the superconducting mechanisms.

  The new Hg-bearings series, HgBa2Ca1-nCunO2n+2+d , is also very promising because its members exhibit the highest Tc's. For example, for n = 1, 2, and 3, Tc (onset) is 94, 126, and 134 K, respectively.

  The technique of relating the twin structure of 123 samples with the critical current density, developed by the Darmstadt group, also has good potential.

  Latest Publications

  • Ren Y, Schmahl W W, Brecht E and Fuess H Intergrain flux-pinning in relation to structural phase transformation and tweed formation in YBa2(Cu1-xFex)3O7-y Physica C 199, 414-424 (1992)
  • Liu R S, Hervieu M, Michel C, Maignan A, Martin C, Raveau B and Edwards P P The variation in microstructure for the Tl2Ba2Ca2Cu3O10-8 phase with Tc of 119 and 127 K Journal of Solid State Chemistry 100, 186 (1992)
  • Bordet P, Chaillout C, Fournier T, Marezio M, Kaldis E, Karpinski J and Jilek E Evidence by x-ray diffraction for two apical oxygen sites in a copper-dificient YBa2Cu2.78O7 Physical Review B 47, 3465-3468 (1993)
  • Maignan A, Van Tendeloo G, Hervieu M, Michel C and Raveau B A new "1212" mercury-based superconductor Y0.6Ca0.6Ba2[Hg1-xMx]Cu2O6+y Physica C, 212, 239 (1993)
  • Krekels T, Milat O, Van Tendeloo G, Van Landuyt J, Amelinckx S, Slater P R, Greaves C SO4 chain formation and ordering in (Y,Sr,Ca)Sr2Cu2.78(SO4)0.22O7-8 Physica C, 210, 439 (1993)

  Information Dissemination Activies

  The research on high Tc superconductivity carried out within the framework of the Working Group is published in international journals such as Physica C, Nature, Journal of Solid State Chemistry, Physical Review, etc. and presented at international meetings, where very often the members of the WG are invited speakers.

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  Coordinator

  CNRS - F
  Laboratoire de Cristallographie
  BP 166
  F - 38042 GRENOBLE CEDEX 09
  

  Participants

  RUCA Antwerpen - B
  ETH Zürich - CH
  Technische Hochschule Darmstadt - D
  Ris_ National Laboratory - DK
  Università Complutense Madrid - E
  CRISMAT CAEN - F
  NCSR Demokritos - GR
  Università di Parma - I
  Trinity College Dublin - IRL
  Universiteit Delft - NL
  Istituto Superior Tecnico - P
  University of Birmingham - UK
  

  CONTACT POINT

  Dr. M. Marezio
  tel +33/76 88 10 40
  fax +33/76 88 10 38
  

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  HTSC - 6885, August 1994

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  html version of synopsis by Nick Cook