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

The Ca2+ and Ba2+ solubility on Nd2+ sites in new layered perovskite NdBaInO4 mixed oxide ionic and hole conductor and their effect on the oxide ion conductivity of NdBaInO4 were investigated. Among the alkaline earth metal cations Ca2+, Sr2+, and Ba2+, Ca2+ was shown to be the optimum acceptor-dopant for Nd3+ in NdBaInO4 showing the largest substitution for Nd3+ up to 20% and leading to oxide ion conductivities similar to 3 X 10(-4)-1.3 X 10(-3) s/cm within 600-800 degrees C on Nd0.8Ca0.2BaIn03.9 composition, exceeding the most conducting Nd0.8Sr0.1BaInO3.95 in the Sr-doped NdBaInO4. Energetics of defect formation and oxygen vacancy migration in NdBaInO4 were computed through the atomistic static-lattice simulation. The solution energies of Ca2+/Sr2+/Ba2+ on the Nd3+ site in NdBaInO4 for creating the oxygen vacancies confirm the predominance of Ca2+ on the substitution for Nd3+ and enhancement of the oxygen vacancy conductivity over the larger Sr2+ and Ba2+. The electronic defect formation energies indicate that the p-type conduction in a high partial oxygen pressure range of the NdBaInO4-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 NdBaInO4. Molecular dynamic simulations on the Ca-doped NdBaInO4 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.