Oxide Ion Conduction, Defect Chemistry, and the Conducting Mechanism in Ruddlesden–Popper La2–xMxBaIn2O7–0.5x (M = Ca, Sr, Ba)

Tetragonal La 2 BaIn 2 O 7 belongs to the stoichiometric n = 2 members of the Ruddlesden–Popper (RP) structure, with La 3+ and Ba 2+ cations ordered in the rock salt and octahedral layers, respectively. Herein, a series of alkaline-earth-metal-doped materials La 2– x M x BaIn 2 O 7–0.5 x (M = Ca, Sr, Ba) were prepared by the traditional solid-state reaction method. The results revealed that the substitutions of Ca/Sr/Ba for La introduced oxygen vacancies and led to good oxide ion conduction, e.g., ∼1.21 × 10 –3 –1.38 × 10 –2 S/cm within 600–900 °C for the specimen La 1.7 Ba 1.3 In 2 O 6.85, which was more than 2 orders of magnitude higher than the parent material. However, both the parent and acceptor-doped La 2 BaIn 2 O 7 showed very limited proton conductions. The energetics of defect formation and oxygen vacancy migrations in La 2 BaIn 2 O 7 -based materials was studied through the static lattice and molecular dynamics (MD) atomistic simulations based on the interatomic potential approach. The defect formation energy calculations for the electrons and holes in La 2 BaIn 2 O 7 rationalized the experimentally observed pure ionic conduction under low pO 2 and mixed ionic and p-type electronic conductions under high pO 2, respectively. The MD simulations indicated two-dimensional oxygen vacancy migration within the perovskite slab for the acceptor-doped La 2 BaIn 2 O 7 .