Flexibility windows and compression of monoclinic and orthorhombic silicalites

Silicalite, a high-silica zeolite with MFI topology, undergoes pressure-induced amorphisation (PIA) when compressed with nonpenetrating pressure media. PIA is prevented by penetrating pressure media. In several zeolites, links have recently been found between pressure-induced phase transitions and the flexibility window, a geometric property of the framework identified by geometric simulation. We have analyzed structural data from compression experiments on silicalite, and we find that PIA occurs while the structure lies within its flexibility window. Penetrating media, which prevent PIA, push the structure outside the flexibility window. Thus framework flexibility is required for PIA to occur in silicalite. This link between amorphisation and flexibility is further evidence of the deep connections between framework geometry, flexibility, and the physical properties of zeolites.