Framework and Channel Modifications in Mayenite (12CaO·7Al₂O₃) Nanocages By Cationic Doping

Mayenite (Ca 12 Al 14 O 33, C 12 A 7 ), and its electride variant (C 12 A 7:2e – ) have attracted attention as functional materials with high ionic conductivity, and for potential uses in oxidation catalysis, fuel cells, and hydrogen storage. In contrast to anionic substitutions into C 12 A 7, less is known about the influence of cationic substitutions on this material. This study applies DFT methods to rigorously understand the influences of Mg 2+, Cu 2+, Sr 2+, Fe 3+, Ir 4+, P 5+ and V 5+ (2+ ≤ Z V ≤ 5+, where Z V is the cation valence, unitless) substitutions on the structural and electronic features of C 12 A 7 and its electride variant. Substitutions alter the lattice parameters, in relation to their size, and alter charge localization. Substitutions also affect mayenite’s cage framework, resulting in the formation of a “window” that connects two adjacent cages. While Mg 2+, Sr 2+, P 5+, and V 5+ substitutions maintain their F + -like attractive nature, Cu 2+, Fe 3+, and Ir 4+ neutralize such a tendency in the cages of their corresponding C 12 A 7 electride. Therefore, the conduction mechanism of mayenite electride (i.e., containing Cu 2+, Fe 3+, and Ir 4+ ) switches from e – -hopping to band conduction electrons. The insertion of Cu 2+ -substitutions makes the window between two adjacent nanocages collapse, resulting in the formation of a transport channel between two neighboring [Ca–Al–O] cages for localized electrons. The outcomes suggest novel means to induce electron coupling between nearest-neighbor cages in mayenite, an aspect of interest for tailoring the electron transport properties of mayenite and other light-metal oxide electrides.