Discovery of the flexibility window has been a major breakthrough in zeolite science and led us to further study the properties of zeolites under high-pressure. There has been a wide range of studies in the last 40-50 years on the high-temperature behavior of zeolites, to our surprise this was not matched by high-pressure studies. A lack of high-resolution high-pressure structures is astounding.
With our close collaborator Dr. Diego Gatta, we have been looking at the flexibility windows of dense zeolites under pressure. We looked at analcime, leucite and wairakite, where we found that flexibility window controls the structural phase transitions in all three zeolites.
With our collaborator Dr. Julien Haines, we have looked at silicalite under pressure. Silicalite has an MFI framework. We demonstrated a link between pressure-induced amorphisation and the flexibility window. During compression with non-penetrating pressure media, amorphisation in silicalite proceeds over a range of pressures. We found that during this process the crystalline portions of the structure remain outside the window and force distortions in the polyhedra.
We have also collected some high-pressure data with Dr. Andrew Caines (ESRF) on synthetic EMC-2 with and without oSDAs. Paper forthcoming.