Defect structure, thermodynamic and transport properties of SrCo0.9Nb0.1O2.5+δ: A combined experimental and defect chemistry approach

In this work, a new methodology is presented to derive the thermodynamic and transport properties of 10 mol% Nb-doped SCO (SCN10) system by combining a new defect chemistry model with experimental electrical conductivity and oxygen nonstoichiometry data. Built on a perfect Brownmillerite SrCoO2.5 reference framework, the defect model features oxygen interstitials at tetrahedral sites and oxygen vacancies at octahedral sites as the ionic point defects, and electrons and holes as the electronic point defects. The thermodynamic properties of the oxygen incorporation, Frenkel lattice oxygen exchange and cobalt disproportionation reactions are obtained from oxygen nonstoichiometry data δ(T, PO2). The concentration contours of all the ionic and electron defects are mapped out on the T-PO2 domain. The partial/integral molar thermodynamic properties as well as thermodynamic factor of the SCN10 solid solution are also determined. Furthermore, by combining the concentrations of point defects and the experimental electronic conductivity, mobilities of electrons and holes are obtained as a function of temperature. We expect that the method developed in this study is applicable to other types of mixed conducting complex oxides.