Acceptor Doping and Oxygen Vacancy Migration in Layered Perovskite NdBaInO₄-Based Mixed Conductors

Abstract

The Ca 2+ and Ba 2+ solubility on Nd 3+ sites in new layered perovskite NdBaInO 4 mixed oxide ionic and hole conductor and their effect on the oxide ion conductivity of NdBaInO 4 were investigated. Among the alkaline earth metal cations Ca 2+, Sr 2+, and Ba 2+, Ca 2+ was shown to be the optimum acceptor–dopant for Nd 3+ in NdBaInO 4 showing the largest substitution for Nd 3+ up to 20% and leading to oxide ion conductivities ∼3 × 10 –4 –1.3 × 10 –3 s/cm within 600–800 °C on Nd 0.8 Ca 0.2 BaInO 3.9 composition, exceeding the most-conducting Nd 0.9 Sr 0.1 BaInO 3.95 in the Sr-doped NdBaInO 4 . Energetics of defect formation and oxygen vacancy migration in NdBaInO 4 were computed through the atomistic static-lattice simulation. The solution energies of Ca 2+ /Sr 2+ /Ba 2+ on the Nd 3+ site in NdBaInO 4 for creating the oxygen vacancies confirm the predominance of Ca 2+ on the substitution for Nd 3+ and enhancement of the oxygen vacancy conductivity over the larger Sr 2+ and Ba 2+ . The electronic defect formation energies indicate that the p-type conduction in a high partial oxygen pressure range of the NdBaInO 4 -based materials is from the oxidation reaction forming the holes centered on O atoms. Both the static lattice and molecular dynamic simulations indicate two-dimensional oxygen vacancy migration within the perovskite slab boundaries for the acceptor-doped NdBaInO 4 . Molecular dynamic simulations on the Ca-doped NdBaInO 4 specify two major vacancy migration events, respectively, via one intraslab path along the b axis and one interslab path along the c axis. These paths are composed by two terminal oxygen sites within the perovskite slab boundaries.