Effects of temperature on the electrical properties of samaria-doped ceria predicted with the statistical moment method

Abstract

Samaria-doped ceria (SDC) is an important candidate electrolyte for use in solid oxide fuel cells, but the effect of lattice thermal vibrations on its electrical properties are unclear. In this study, the statistical moment method was employed to predict the temperature dependences of vacancy–dopant association, migration and activation energies, and ionic conductivity in four theoretical regimes comprising static, harmonic, semi-classical anharmonic, and quantum anharmonic regimes. The lattice thermal vibrations weakened vacancy–dopant associations and significantly inhibited vacancy hopping, and these effects were more pronounced as the temperature increased. The strongest vacancy–dopant associations and less convenient movement of oxygen vacancies could occur in the crystal lattice including anharmonic vibrations. Considerable enhancement of the ionic conductivity and a shift in the optimal dopant concentration toward higher values were found in the harmonic regime. Increasing the temperature also led to similar changes in the ionic conductivity. The maximum ion conductivity was governed by trapping and blocking effects, but also by lattice thermal vibrations. The results indicated the trivial influence of quantum effects in the anharmonic vibrations on the electrical properties. These findings provide a deeper understanding of the underlying atomistic mechanisms that determine the effects of temperature and lattice thermal vibrations on the electrical properties, and they may be beneficial for optimizing the ionic conductivity of SDC electrolytes.