Density functional theory study on the electronic structure ofn- andp-type doped SrTiO3at anodic solid oxide fuel cell conditions

Abstract

The electronic conductivity and thermodynamic stability of mixed $n$-type and $p$-type doped SrTiO${}_{3}$ have been investigated at anodic solid oxide fuel cell (SOFC) conditions using density functional theory (DFT) calculations. In particular, constrained ab initio thermodynamic calculations have been performed to evaluate the phase stability and reducibility of various Nb- and Ga-doped SrTiO${}_{3}$ at synthesized and anodic SOFC conditions. The density of states (DOS) of these materials was analyzed to study the effects of $n$- and $p$-doping on the electronic conductivity. In agreement with experimental observations, we find that the transformation from 20$%$ Nb-doped Sr-deficient SrTiO${}_{3}$ to a non-Sr-deficient phase occurs at high temperature and low oxygen partial pressure, which leads to a significant improvement in electronic conductivity. A mixed ionic/electronic conductor is obtained when doping 20$%$ Nb-doped SrTiO${}_{3}$ with small amounts of Ga (10$%$) in a reducing environment and high temperature. Doping with higher concentrations of Ga, e.g., 20$%$, diminishes the electronic conductivity of the material. These findings suggest that independent of the specific dopant, mixed ionic/electronic conductivity can be obtained in perovskite oxides under reducing conditions and high temperatures by doping the B-site with small amounts of both $n$-type and $p$-type dopants.