Thermal transport properties in the normal state of CaAlxSi2−x superconductors

Normal state electrical and thermal properties, including electrical resistivity (ρ), Seebeck coefficient (S), and thermal conductivity (κ) of the CaAlxSi2−x (x=0.9-1.2) system were investigated. It is found that the electrical resistivity and Seebeck coefficient exhibit a typical metallic character throughout the temperature range investigated, and the metallicity of this series is enhanced with increase in Al/Si ratio. On the other hand, the thermal conductivity shows a weak temperature variation at low temperatures, whereas κ follows a T 2-dependence for T>150 K. Analysis of the electronic thermal resistivity based on Klemen's model reveals that the scattering of electrons from the defects and static imperfections becomes dominant as the temperature approaches Tc. These results are discussed in the light of simultaneous existence of various crystal structures and development of ultra-soft phonon mode recently observed in the CaAlSi system.