Thermal conductivity, thermopower, and figure of merit of La1-xSrxCoO3 -: art. no. 155116

We present a study of the thermal conductivity kappa and the thermopower S of single crystals of La1-xSrxCoO3 with 0 <= x <= 0.3. For all Sr concentrations, La1-xSrxCoO3 has rather low kappa values. For the insulators (x < 0.18) this arises from a suppression of the phonon thermal conductivity by lattice disorder due to temperature- and/or doping-induced spin-state transitions of the Co ions. For larger x, the heat transport by phonons remains low, but an additional contribution from mobile charge carriers causes a moderate increase of kappa. The thermopower of the low-doped crystals is positive and shows a pronounced maximum as a function of temperature. With increasing x, this maximum broadens strongly and its magnitude decreases. For the highest Sr content (x=0.3), S becomes negative in the intermediate temperature range. From S, kappa, and the electrical resistivity rho, we derive the thermoelectric figure of merit Z=S-2/kappa rho. For intermediate Sr concentrations we find notably large values of Z, indicating that Co-based materials could be promising candidates for thermoelectric cooling.