High Temperature Thermoelectric Response of Electron-Doped CaMnO3

We report a systematical investigation on the high temperature thermoelectric response of Ca1-xRxMnO3 (R = rare-earth) perovskites in the electron-doped range. The results reveal that electron concentration is the dominant factor for the high temperature electrical transport properties whereas the weight and size of R ions dominate the thermal transport properties. As the doping level varies, the best thermoelectric performance is observed at the relative electron concentration around 0.1. However, in the case of a fixed electron concentration, structural distortions become important since bandwidth has an observable influence on resistivity. By combining the three factors, electron concentration, crystal structure, and the weight/size of R ions, the largest thermoelectric figure of merit ZT for Ca1-xRxMnO3 reaches 0.2 at 1000 K. But this ZT value is still too far from the application criterion (ZT > 1). Using the dynamical mean field theory, we demonstrate that a ZT value larger than one in electron-doped CaMnO3 systems seems rather unlikely. Some strategies for searching new thermoelectric materials with high performance in transition metal oxides are proposed.