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: