Thermal conductivity and electrical resistivity of cemented carbides, titanium diboride and high temperature ceramic superconductors

It has been reported that YBa{dollar}sb2{dollar}Cu{dollar}sb3{dollar}O{dollar}sb{lcub}rm 7-x{rcub}{dollar} exhibits a significant rise in thermal conductivity just below the superconducting transition temperature, T{dollar}sb{lcub}rm c{rcub}{dollar}. This rise, or phonon bump, has been attributed to decreased scattering of phonons by electrons. The phonon bump in a high temperature superconductor is here quantitatively analyzed for the first time. The effect is attributable to a factor of two decrease in phonon-electron scattering below as compared to above T{dollar}sb{lcub}rm c{rcub}{dollar}. Thus phonon-electron scattering in YBa{dollar}sb2{dollar}Cu{dollar}sb3{dollar}O{dollar}sb{lcub}rm 7-x{rcub}{dollar} appears to play a part in lattice thermal resistance even in the superconducting state. The small phonon bump in YBa{dollar}sb2{dollar}Cu{dollar}sb3{dollar}O{dollar}sb{lcub}rm 7-x{rcub}{dollar} is to be contrasted with the dramatic rise in lattice thermal conductivity of superconducting NbC{dollar}sb{lcub}rm x{rcub}{dollar}, which increases two orders of magnitude as NbC{dollar}sb{lcub}rm x{rcub}{dollar} passes through T{dollar}sb{lcub}rm c{rcub}{dollar}.; Electrical resistivity measurements of the Bi-Sr-Ca-Cu-O superconducting system with different compositions show interesting behaviors. Two compositions exhibit resistivity saturation below room temperature. All compositions contain a phase which demonstrates a superconducting phase transition at 85{dollar}spcirc{dollar}K; one composition manifests a superconducting phase transition at 115-120{dollar}spcirc{dollar}K.; In cemented carbides it is found that phonon and electron scattering from defects is the dominant cause of variations in thermal and electrical conductivity above 80{dollar}spcirc{dollar}K. Cemented carbides made primarily of nostoichiometric cubic carbides possess a dramatically lower thermal conductivity than WC-based cemented carbides.; An increase in amount of binder phase lowers the thermal conductivity of a cemented carbide. This effect is ascribed to phonon and electron scattering from dissolved W and C atoms in the binder phase.; An increase in carbide grain size increases the thermal conductivity of a cemented carbide. This effect is attributed to an increase in carbide grain contiguity and the dominant role of the carbide phase in thermal conduction in WC-based cemented carbides. This conclusion is strengthened by the observation of a large decrease in thermal conductivity with the addition of a third phase of a solid solution of nonstoichiometric cubic carbide grains.; In high purity polycrystalline titanium diboride it is found that scattering of phonons and electrons from defects is an important cause of thermal resistivity. The scattering centers are boron vacancies and particles of elemental carbon. (Abstract shortened with permission of author.)...