Thermoelectric materials are used to cleanly convert waste heat into electrical energy. Their performance favors high electrical conductivity, large Seebeck coefficient, and low thermal conductivity. CaO(CaMnO3)m compounds are promising due to their intrinsically low thermal conductivity, e.g. 0.75 W m-1 K-1 at 900 K [1], which is associated to internal rock-salt CaO layers residing between adjacent CaMnO3 perovskite sub-cells. This study is aimed at increasing the electrical conductivity of Ca2-xRxMnO4 bulk materials, where R = La or Y and 0.01 ≤ x ≤ 0.20, by doping which is intelligently based on density functional theory (DFT) simulations. We show that substitution of Y for Ca lowers the total lattice potential at CaO layers compared to La-substitution. Thereby, we prepare Ca2MnO4 specimens doped with either Y or La applying standard solid-state reaction routines and sintering [2], and characterize their crystal structure, charge carrier concentration, and electronic transport coefficients in the range of 300-1000 K. It is found that Y-doping generally facilitates electronic transport compared to La-doping by up to two times. This trend is elucidated in terms of the small polaron hopping model, indicating that Y-doping reduces the conduction activation energy by up to 18 % in the range of 300-750 K compared to La-doping. Our results suggest that energy barriers for electronic transport in oxides may be tailored by point defect engineering.

1. A. Baranovskiy, A. Graff, J. Klose, J. Mayer and Y. Amouyal, Nano Energy 47, 451-462 (2018).
2. A. Azulay and Y. Amouyal, Acta Mater. 164, 481-492 (2019).