Thermal conductivity of (Pr1-x REx0.7Ca0.3CoO3 (RE=Sm, Gd) around metal-insulator - spin-state transition

Abstract

We have measured the electrical resistivity, p(T), and thermal conductivity, κ(T), as a function of the temperature for polycrystalline (Pr1-xREx)0.7Ca0.3CoO3 (RE=Sm, Gd). p(T) shows a sharp jump below the metal-insulator (M-I) transition temperature, TM-1, at which the spin-state transition of the Co3+ ions simultaneously takes place with decreasing temperature from the excited (intermediate spin (IS) or high spin (HS)) state to the low spin (LS) state. κ(T) shows a broad peak below TM-I with a slight decrease just above TM-I. The κ(T) peak originates from the decrease of the phonon scattering due to the spin-state transition from Jahn-Teller (JT) active Co3+ (IS or HS) to non JT Co3+ (LS). The phonon scattering mechanism around TM-I is discussed.