Structural analyses of intergrowth and stacking fault in cage-type mesoporous crystals

A mixture of Gemini Cationic surfactant, costructure directing agent (CSDA) with carboxylate group, and silica oligomerleads to the formation of cage-type mesoporous crystals, and the system changes the structure from Fm3m (or P6 ₃/mmc ) type to Fd3m type with an increasing amount of additive (HC1). Here we have investigated the Fm3m-Fd3m type intergrowth and new type stacking fault observed in the intermediate phase using transmission electron microscopy (TEM) and proposed a layer-by-layer growth mechanism. In order to describe the structures, four types of polyhedra for the tetrahedrally close-packed structures are introduced. In the intergrowth, the structure changes the packing of spherical micelles between the Fraim (or P6 ₃/mmc ) and Fd3m structures depending on the pH. The results can be explained by the change between a hard sphere characteristic ( perfect sphere) in the Fm3m structure and a soft sphere characteristic (polyhedron) in the Fd3m structure. The stacking fault in the Fd3m structure can be explained by new arrangement of two polyhedra, the 14- and 15-hedron.