Mapping of perovskite oxides in the localized vs itinerant electron diagram and its relation with the ionic conductivity

The electronic properties of perovskite-type oxides ABO3 can be characterized by the degree of localization of d-electrons. On the other hand, the complex perovskite oxides A1 − xA′xB1 − yB′yO3 − δ exhibit ionic conduction through the defects created by partial substitution of metal atom A and (or) B. In the present study, the relationship between the ionic conduction and the nature of electronic transport properties in perovskite-type oxides is discussed by extending the classification scheme of localized and itinerant d-electron diagram used for ABO3 compounds. The classification scheme is based on the potential parameter Z/r, where Z and r are the valence and ionic radii of the cation. From the analysis, it is found that in perovskite oxides, the oxygen ionic conductivity decreases with ZA/rA of ion A. The result indicates that the nature of the electronic state influences the ionic conduction. An interpretation of the result found in terms of the bond fluctuation model of superionic conductors is given.