Oxygen Mobility in Compositional Variants of Mayenite

Ca₁₂Al₁₄O₃₃ (mayenite) is a mineral with a positively charged framework of cages partially occupied by anions. Oxygen mobility in mayenite has been broadly studied, unlike its isostructural compounds Ca₁₂Ga₁₄O₃₃ and Sr₁₂Al₁₄O₃₃, which each replace one of the species of framework cations with a larger ion, leading to larger cages and interesting behavior. Ca₁₂Al₁₄O₃₃, Ca₁₂Ga₁₄O₃₃, and Sr₁₂Al₁₄O₃₃ were modeled with classical molecular dynamics to investigate the movement of oxygen through their structures at 77, 300, 700, and 1673 K. Oxygen ions were observed to move through the structure along different pathways, with preferences based on the cations involvedCa₁₂Ga₁₄O₃₃ through exchanges between caged and framework oxygens, and Ca₁₂Al₁₄O₃₃ through a combination of the exchanges and passing through windows of the cages. Sr₁₂Al₁₄O₃₃ showed some exchange but little overall oxygen mobility at the temperatures studied.