Thermoelectric response driven by spin-state transition in La _1-xCe_xCoO₃ perovskites

An unusual thermoelectric response was observed in n-type perovskite oxide La_1-xCe_xCoO₃. Combining transport and magnetic measurements, we found that the thermoelectric response is driven by the spin-state transition of Co³⁺. This transition destroys the spin blockade effect and induces an abrupt decrease of resistivity as well as an insulator-metal transition. In contrast to the resistivity change, changes in thermopower and thermal conductivity are moderate. Consequently, a peak of figure of the merit ZT is present in a narrow temperature range. The room-temperature ZT ≈ 0.018 of La_0.94Ce_0.06CoO ₃ is comparable to that of p-type Na_xCoO₂. These observations can be helpful for the search and design of new thermoelectric materials.