12CaO7Al2O3

12CaO7Al2O3, commonly written as 12CaO·7Al2O3 or Ca12Al14O33, is a calcium aluminate oxide known as mayenite. It is a white, refractory ceramic oxide that has attracted attention for its distinctive cage-like crystal structure and its ability to host electrons or other anions within its framework.

Structure: The crystal structure consists of a framework of AlO4 tetrahedra and AlO6 octahedra linked by oxide ions to form a porous lattice. Within this network there are multiple interstitial sites occupied by calcium ions; in a unit cell there are 12 cages that can accommodate oxide ions or, upon reduction, electrons, giving rise to electrides such as C12A7:e-.

Synthesis and natural occurrence: Mayenite can be synthesized by high-temperature solid-state reactions of calcium carbonate and aluminum oxide, typically around 1300–1700 C. The natural mineral mayenite, Ca12Al14O33, occurs in the Mayen region of Germany but is rare; synthetic material is widely produced for research and industrial use.

Properties and applications: It is chemically stable, with a high melting point and insolubility in water. In materials science it serves as a refractory oxide and as a precursor for calcium aluminate cements. Its cage structure enables trapping of ions and, when doped, formation of an electride with unusual electronic conductivity, explored for catalysis, energy storage, and electronic applications.