THERMODYNAMIC AND OTHER PROPERTIES OF THE SUPERCONDUCTORS BAPB0.7BI0.3O3 AND BA0.7K0.3BIO3

Results of a thermodynamic analysis are presented for the superconduct ors BaPb0.7Bi0.3O3 and Ba0.7K0.3BiO3. The physical quantities are calc ulated by numerical solutions of the Eliashberg gap equations with the electron-phonon spectra alpha(2)(omega)F(omega) as calculated by Shir ai et al., using a realistic electronic band-structure determined by t he tight-binding approximation. For the superconductor BaPb0.7Bi0.3O3, several models of the alpha(2)(omega)F(omega) were studied looking fo r a better agreement with experimental data. The best fit is achieved with a simple constant scaling (C = 1.25) of the Shirai's spectra. We also calculated the functional derivatives for the critical temperatur e T-c, the critical magnetic field H-c(O), and the deviation function D(t) with respect to changes in alpha(2)(omega)F(omega).