Chloride‐Ion‐Stabilized Strontium Mayenite: Expansion of Versatile Material Family

Sr-mayenite (S12A7) incorporating Cl− ions in its crystallographic cages up to the theoretical maximum occupancy, Sr12Al14O32Cl2, is reported in our study. The addition of a stoichiometric amount of SrCl2 to the starting mixture is effective for the formation of Sr12Al14O32Cl2 with high phase purity. Almost 100% densification is achieved using spark plasma sintering (SPS). Evaporation of SrCl2 from Sr12Al14O32Cl2, which becomes significant at sintering temperatures above ~1300°C, degrades the phase purity. However, SrCl2 effusion is significantly suppressed in the samples fully densified by SPS, impeding the decomposition of Sr12Al14O32Cl2 up to temperature as high as ~1400°C. The crystal structure of Sr12Al14O32Cl2 was investigated by Rietveld analysis of the X-ray diffraction pattern. It is found that the Cl− ion is incorporated in the center of the inner cage with nearly theoretical maximum occupancy, which is responsible for the phase stability. Porous Sr12Al14O32Cl2 exhibits humidity-sensitive surface protonic conductivity. Dense Sr12Al14O32Cl2 prepared under reducing conditions such as SPS exhibits electronic conductivity. Sr-mayenite has various potential applications derived from its multifunctionalities.

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