[en] The discovery of superconductivity in the cuprates produced an explosive growth in research, driven by the quest for higher and higher superconducting transition temperatures. In the initial stages, the excitement was tremendous both in the physical sciences and in engineering. However, the complexity of the new materials on the one hand, and the absence of a viable theory on the other, have made further developments much more difficult. It is to be expected therefore, that the early excitement and the subsequent rapid advances have paved the way for more systematic and detailed studies of all aspects of superconductivity. The International Symposium was intended to provide a forum to review the progress in selected areas in superconductivity. The emphasis was on experimental and theoretical studies of the new superconductors, advances in the theoretical understanding, progress in studies of flux pinning and vortex dynamics which affect critical currents, and developments of novel material synthesis methods. Recent developments in the twin areas of thin films and devices were extensively discussed during the symposium. Papers relevant to INIS are indexed separately

[en] The design considerations for high temperature superconducting microwave filters are presented. The filter designed is at C- band with 0.6% bandwidth. The error analysis, insertion loss calculation, power handling capability, input/output connections and package design are discussed. Theoretical calculations gave insertion loss of 0.8 dB at 6 GHz for a conductivity ratio of 50 between high T_c thin film and gold film. (author)

[en] The quaternary chalcogenides SnBi_4-xTe_3-ySe_4-z and PbBi_4-x Te_3-ySe_4-z have been prepared and found to posses orthorhombic structure. The chemical composition of materials is confirmed by EDX. SnBi_4-xTe_3-ySe_4-z and PbBi_4-xTe_3-ySe_4-z exhibit a low resistivity 0.012 ohm.cm and 0.133 ohm.cm at room temperature and carrier concentration 1.62 x 10¹⁶ and 2.34 x 10¹⁶ cm^-3 respectively. The Hall measurements show n-type behaviour with carrier mobility 3036 and 1670 M²/V, and band gaps by diffuse reflectance are found to be 4.01 eV and 3.99 eV for SnBi_4-xTe_3-ySe_4-z and PbBi_4-xTe_3-ySe_4-z, respectively. (author)

[en] It is well known that the anisotropy and wave-vector dependence of the energy-gap function determine many important properties of a superconductor which are relevant for device applications. Apart from a weak dependence on the wave-vector k^-> in the direction perpendicular to the reciprocal layer-plane of a high-T_c layered superconductor, it is shown that anisotropic superconducting order parameters for intra-layer pairing in the class of such materials with orthorhombic crystal structures, can have either pure s-wave like symmetry or mixed d-wave and anisotropic extended s-wave like symmetries in the reciprocal layer-plane. However, in such materials with tetragonal crystal structures, it is possible to have a pure s-wave like symmetry, which may be either isotropic or anisotropic in the layer k^->-space, or a pure d-wave like symmetry, as far the k^->-dependence in the reciprocal layer plane is concerned. In view of this, some suggestions for analysing experimental data will also be presented. (author)

[en] Preliminary analysis of small angle neutron scattering (SANS) data from the flux line lattice (FLL) in a niobium crystal reveals structural disordering near the peak effect in the transport critical current. The disordered FLL seen in field cooled experiments is a structure that has long been used to understand transport data in this regime. However, these SANS data represent the first direct measurements of all three correlation lengths-one longitudinal and two transverse-through the peak effect. In the vicinity of the peak effect, first positional, then orientational order disappear. The longitudinal correlations, which are much longer, have a weak maximum in the vicinity of the peak effect. These static structural data give an insight into the highly disordered flux line structures near the peak effect, but do not distinguish between vortex glass and pinned liquid phases. Dynamic SANS data could, in principle, be used to define the precise nature of the vortex phases in this regime. (author)

[en] Subgap structure at a bias voltage corresponding to odd submultiple of gap energy 2Δ is observed in the I-V characteristics of Nb-AlO_x-Nb Josephson tunnel junction at 1.2K. It is argued that the observation of this structure at a voltage bias of 2Δ/3e in our junctions cannot be explained by mechanisms such as multiple particle tunneling and multiple Andreev reflections. A qualitative explanation for the occurrence of this structure has been offered within the framework of Josephson self coupling mechanism. (author)

[en] Various experiments have indicated that the order parameter in the high-Tc cuprates has a predominant d_x²-y² symmetry. This has important implications for devices based on Josephson junctions. The d_x²-y² symmetry leads for example to intrinsic weak link formation, inhomogeneous current distributions in the junctions and reduced I_cR_n products. This article points out the implications a d_x²-y² symmetry component has for Josephson junction devices, with particular emphasis on devices based on grain boundaries in high-T_c superconducting thin films. (author)

[en] The relation among the crystal structure, electronic structure and superconductivity in high temperature superconducting cuprates is reviewed. (author)

[en] Soon after the discovery of superconductivity at 92K in YBa₂Cu₃O₇, it was shown that Pr suppressed superconductivity in Y_1-xPr_xBa₂Cu₃O₇ when the concentration of Pr exceeded a critical value X_c of 0.55. Further, the value of X_c depended on the ionic radius of the rare earth (at the Y site), X_c being as low as 0.3 for Nd. Several models have been proposed to account for these data but without much success. In the first part we will review the experimental data obtained since 1987. In the second part of this paper, recent results obtained in the last year on the effect of isovalent Sr substitution at the Ba site on x_c will be presented. In particular, it was shown that X_c could be increased from 0.3 to 0.45 when 50% of Ba was substituted by Sr in Nd_1-xPr_xBa₂Cu₃O₇. Further, heating the samples in argon prior to oxygen annealing increased the T_c by 6 to 15K depending on x. In addition, annealing in high pressure oxygen induced superconductivity in certain insulating samples. The normal state properties including Seebeck coefficient will be reported. Neutron diffraction studies indicated a relative slow variation of apical oxygen distance as a function of x(Pr) in Sr substituted systems. In the third part these data will be discussed in the light of certain theoretical models invoking the effect of Prf-CuO₂ hybridisation. Our data show that Sr retards this hybridisation and in addition stress the important role played by oxygen reordering along the chains in the Pr substituted Ln123 compounds. (author)

[en] A survey is given of experiments on low T_c superconductors. Although it is generally agreed that the ease of flux cutting determines critical currents, vortex instabilities lead to complex structures for which there is no satisfactory theory. In high T_c superconductors there has been little evidence of the effects of flux cutting. This is probably due both to the presence of weak links in granular materials and the layered structure of single crystals. In both YBCO and BSCCO the material behaves above the irreversibility line as a standard anisotropic resistive material. However the fact that the c-axis and ab activation energies are very similar, and also much greater than kT gives important clues as to the transport mechanism. (author)