Temperature dependence of thermodynamic properties of spinel CuIr2S4

We have investigated the thermodynamic and electrical properties of spinel CuIr2S4. The temperature, T, dependence of the electrical resistivity rho(T), thermal conductivity, kappa(T), and thermoelectric power, S(T), show the abrupt jumps with the relative large hysteresis at a metal-insulator transition temperature T-MI similar to 230 K, with decreasing T. The acoustic-Debye model can fit kappa (T) in the insulating phase(T < T-MI). On the other hand, kappa(T) in the metallic phase (T-MI < T) can be reproduced by the Debye model adopting the optical phonon contributions. S(T) is described qualitatively by the one calculated using the simplified diffusion thermoelectric power formula with the density of state. The enhancement of S(T) in T < T-MI is caused by the existence of the small gap at the Fermi level. The dimensionless figure of merit, ZT, from rho(T), kappa(T), and S(T) shows abrupt jump at T-MI, and the linear increase with increasing T.