A new defect chemistry model featuring oxygen interstitials (OI) and delocalized-to-localized d-electron holes (CoCo·) as point defects is demonstrated under a perfect Brownmillerite SrCoO2.5 reference framework to elucidate transport properties of Nb-doped SrCoO2.5+δ (SCN) system over a range of partial pressure of oxygen (Po2) and temperature (T). With this new defect chemistry model, the electronic conductivity behaviors with T and Po2 can be well interpreted by the change in concentration of d-electron holes migrating with a constant mobility. The important concentration contours of electron holes, excess electrons and oxygen interstitials are mapped out on the T-Po2 domain, from which hole-concentration and conductivity under iso-stoichiometry are reconstructed. The partial/integral molar thermodynamic properties and thermodynamic factor of the SCN solid solution are also determined. A transitional delocalized-to-localized hole-transport mechanism with decreasing oxygen stoichiometry is discussed based on p=p(T) obtained under constant oxygen stoichiometry.
Wang, J., Jin, X., & Huang, K. (2017). A new defect chemistry model for Nb-doped SrCoO2.5+δ: The role of oxygen interstitials and delocalized-to-localized electron holes. Journal of Solid State Chemistry, 246, 97–106. https://doi.org/10.1016/j.jssc.2016.11.008