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.