The “template” effect of the extra-framework content on zeolite compression: The case of yugawaralite.

The microscopic behavior of the Ca-zeolite yugawaralite has been studied by ab initio moleculardynamics simulations adopting experimental cell parameters obtained at pressures up to ∼9 GPa.Pressure-induced volume contraction occurs via rotations of quasi-rigid TO4 tetrahedra that reducethe size of the channels in which the extra-framework species are located. Such rotations are governedby deformation of the coordination polyhedron of Ca, which is made up of water and framework Oatoms. Contraction of the Ca-H2O distances is favored at moderate pressure; at higher pressure theshortening of Ca-framework O atom distances becomes prevalent. The hydrogen bond network playsa fundamental role in the overall response to pressure. Our results indicate that the high-P-induceddeformation of the framework structure is strictly correlated to the extra-framework species that actas templates in the compression process.