Structural, electronic and thermoelectric behaviour of CaMnO3 and CaMnO(3-δ)

First principle calculations were employed to investigate the orthorhombic perovskite CaMnO3 and the impact of reduced oxygen content on the electronic, structural and thermoelectric properties. On partial reduction to CaMnO2.75, oxygen vacancies order in a zig-zag arrangement and a further reduction to CaMnO2.5, is predicted to form a brownmillerite-like structure. We found that reduced structures have a Large volume expansion which can be related to the formation of domains and cracking in experimental samples. On calculating the thermoelectric properties, we found that the partially reduced structures have more favourable Seebeck coefficients compared to the highly reduced structures. The structures can aka be separated into two classes based on the resistivity showing Low or high resistance depending on the oxygen vacancies arrangement and content. However none of the intrinsically doped structures shows enhanced power factors and ZT.