12 Synthesis and Thermophysical Characterization of Bismuth based HighT c Superconductors
Dissipation phenomena in high temperature superconductors are directed by the microstructure that builds up during the preparation process. Therefore, detailed investigations of the electrical and thermal transport and ac magnetic susceptibilities in superconductors prepared either in the form of single crystals, thin films or polycrystalline are important for understanding superconductivity as well as for useful applications. The effect of elements (Pb, Fe, Co, Ni, V, Zn) doping in Bi based superconducting materials has been extensively investigated Remschnig et al. 1991; Awana et al. 1992; Maeda et al. 1990; vom Hedt et al. 1994; Pop et al. 1997; Mori et al. 1992; Kim et al. 1992; Gul et al. 2008; Maqsood et al. 1992 It was reported that the superconducting properties of these materials are affected with increase of the amount of doping, regardless of the nature of the dopants. The repression of superconductivity was concluded to be due to local disorder induced by the amount of doping. However, the details of the current limiting means in the Bi 2223 system are not well established. Consequently, it is of interest to try these doping elements in the Bi 2223 system with a different nominal composition, of which we intend to investigate Bi1.6Pb0.4Sr1.6Ba0.4Ca2Cu3Oy in order to provide additional observations to contribute further understanding of their role on the superconductivity of the system. It is well established that ceramic high Tc superconductors include a collection of tiny, randomly oriented anisotropic grains which are connected to each other by a system of so called 'weak links' or 'matrix' The linear temperature dependence of the electrical resistivity is one of the most important characteristics of the normal phase kinetics of high Tc layered cuprates (Batlogg, 1990) In superconductors where the dc electrical resistivity diverges to zero below Tc, the thermal conduction is almost a unique measurement to study the transport properties below Tc. The magnitude and temperature dependence of the thermal conductivity are parameters which have an impact on a broad spectrum of devices. In high TC superconductors, such information is even more valuable to know how the free carriers and lattice vibrations contribute to the transport of heat. Transient Plane Source (TPS) technique is a well