Study of the thermal behaviour of Bi(Pb)Sr(Ba)-2223 high- Tc granular superconductors

Abstract

Thermal measurements were performed to correlate the microstructural and morphological modifications induced by barium doping and the superconducting properties of Bi(Pb)Sr(Ba)-2223 superconductors. The samples were prepared by a solid state reaction method. The samples were then analyzed by dc electrical resistivity, thermal transport and thermoelectric properties all as a function of temperature (from room down to 77 K). X-ray diffraction studies were also done and the lattice constants of the material were determined by indexing the diffraction peaks. All the above measurements showed that in the samples, there exists almost a single high- T c phase with T c,0 ≃ 110 ± 1 K. Samples are investigated for thermal transport properties, i.e. thermal conductivity, thermal diffusivity and heat capacity per unit volume, by an advantageous transient plane source method. Simultaneous measurement of thermal conductivity and thermal diffusivity makes it feasible to estimate specific heat and the Debye temperature Θ D, as well as to separate the electron and phonon contributions to thermal conductivity and diffusivity. Thermoelectric power (Seebeck Coefficient) is measured with newly developed and calibrated apparatus. This newly developed apparatus is easy to use, simple in operation and is interfaced to computer for measurements and calculations. Using electrical resistivity, thermal conductivity and thermoelectric power, the figure of merit factor is calculated.