Self-doping and electrical conductivity in spinel oxides: Experimental validation of doping rules

Self-doping of cations on the tetrahedral and octahedral sites in spinel oxides creates "anti-site" defects, which results in functional optical, electronic, magnetic, and other materials properties. Previously, we divded the III-II spinel family into four doping types (DTs) based on first-principle calculations in order to understand their electrical behavior. Here, we present experimental evidence on two prototype spinels for each major doping type (DT1 and DT4) that test the first principles calculations. For the DT-1 Ga₂ZnO₄ spinel, we show that the anti-site defects in a stoichiometric film are equal in concentration and compenstate each other, whereas, for nonstoichiometric Cr₂MnO₄, a representative DT-4 spinel, excess Mn on the tetrahedral sites becomes electrically inactive as the Mn species switch from (III) to (II). The agreement between experiment and theory validates the Doping Rules distilled from the theoretical framework and significantly enhances our understanding of the defect chemistry of spinel oxides.