Effects of the atmosphere and Mn doping on the electrical properties of Sr2Fe1−xMnxNbO6 and their mechanisms

Double-perovskite composite oxides (A2BB′O6) usually have excellent functional properties and are widely studied and applied. Its electrical, magnetic or other properties can be optimized by doping transition metal elements at its B or B′ site. In this paper, the effects of Mn doping and testing atmosphere on the crystal structures and the electrical conductivities of Sr2Fe1−xMnxNbO6(SFMN) were systematically investigated. The experimental results demonstrate that the conductivities of SFMN will increase in air while decrease under H2/H2O(g) atmosphere with Mn content rise. Doping Mn can enlarge the interplanar spacing of SFMN which increases the resistance of electron conduction across the crystal. First-principles calculations and XPS analysis results reveal that the chemical adsorption of H2 on the surface of SFMN is a key reason for its conductivity increase under H2/H2O(g) atmosphere. The forbidden band width of the reduced state of Sr2FeNbO6 (1.177 eV) is much smaller than that of the oxidation state (1.426 eV). The analysis results suggest that Fe 3d electron transition and exchange interaction between Mn-O-Mn are mainly two possible mechanisms contribute to the electrical conductivity of SFMN.