THERMAL-CONDUCTIVITY OF BISMUTH-LEAD-(2223) SUPERCONDUCTING CUPRATES WITH VANADIUM/NICKEL SUBSTITUTIONS AND EVIDENCE FOR STRONG ELECTRON-PHONON COUPLING

Thermal conductivities of a number of vanadium and nickel substituted 2223 (Bi-Pb)) superconducting cuprates are reported between 10 and 150k. Substitution of both vanadium and nickel in (Bi-Pb) system influence strongly the magnitude of thermal conductivity (k) of the pellets, both above and below T-c. The reduced temperature derivative of the normaliaed conductivity (K-S/K-N) for the reported samples varies between -0.78 and -1.32. Evoking Wiedemann - Franz law the relative magnitude of the carrier and the phonon contributions to total K was estimated. Analysis of K-L data using Tewordt-Wolkhausen expression indicates that for all the samples phonon-defect scattering dominates above T-C. We further calculate the slope of lattice thermal conductivity at T-C and estimate that the slope of carrier thermal conductivity is very large (>8), which indicates strong coupling for some of the carriers in these systems.