Thermal conductivity (and thermoelectric power) of neutron irradiated Bi-based high critical temperature superconductors

Ceramic superconductors with a nominal composition Bi1.5Pb0.5Sr2Ca2 Cu3O10 were irradiated by fast neutrons (E > 0.1 MeV) with fluences up to 2 * 10(18) cm(-2). The thermal conductivity kappa and the thermoelectric power were simultaneously measured by means of a steady flow method. The thermal conductivity magnitude and temperature variation are comparable to data previously reported by other authors. We evaluate that the electron thermal conductivity contributes to no more than 5 % of the measured kappa which is thus dominated by the phonon component. Neutron irradiation increases the density of structural defects. This gradually reduces kappa absolute values in the normal state. The highest fluences reduce the magnitude of kappa and the height of the maximum in the superconducting state. This is accompanied by an electrical resistivity increase. Since the electrical resistivity changes much raster with irradiation fluence than the thermal conductivity does we conclude that the irradiation affects more the electron than the phonon scattering. From the thermoelectrical power data we calculate the Fermi level value which is insensitive to the irradiation.