High temperature transport properties of thermoelectric CaMnO 3-δ - Indication of strongly interacting small polarons

Abstract

The conductivity and Seebeck coefficient of CaMnO3-δ have been studied at temperatures up to 1000 C and in atmospheres with controlled oxygen partial pressure. Both transport coefficients were varied in situ by the reversible formation of oxygen vacancies up to δ = 0.15. The charge carrier concentration was calculated using a defect chemical model. The Seebeck coefficient could be approximated by Heikes' formula, while the conductivity shows a maximum at a molar charge carrier concentration of 0.25. These results were interpreted as a signature of strong electronic correlation effects, and it was concluded that charge transport in CaMnO3-δ occurs via strongly interacting small polarons. General prospects for strongly correlated materials as potential candidates for high temperature thermoelectric power generation were discussed. © 2014 AIP Publishing LLC.