Elastic and thermal transport properties of (Pr1−xSmx)0.7Ca0.3CoO3 at metal-insulator transition

Abstract

In a Pr-Ca-Co-O system, a metal-insulator transition (MIT) accompanied with a spin-state transition (SST) of Co3+ takes place, at which the large volume contraction is also observed because of the tilting of the CoO6 octahedra. To study lattice dynamics at the MI-SST, we have measured the thermal conductivity κ(T), thermal diffusivity α(T), thermal dilatation dL(T)/L and sound velocity v(T) for (Pr1−xSmx)0.7Ca0.3CoO3. κ(T) shows a drop or a kink and α(T) shows a dip around the MI-SST temperature, TMI. v(T) gradually decreases from the higher temperature than TMI and abruptly drops at TMI. About 50 % of the dip of α(T) originates from the decrease of the sound velocity at TMI. The gradual decrease in v(T) above TMI suggests that the anomaly of the lattice linked to the MI-SST starts from fairly higher temperature.