Amorphization of faujasite at high pressure: an X-ray diffraction and Raman spectroscopy study

In situ X-ray diffraction and Raman spectroscopy measurements of synthetic powdered samples of faujasite 13X were carried out at high pressure using diamond anvil cells. Structural changes are detected, linked to a progressive reduction in crystallinity, before complete amorphization of the material. Three distinct compressibility regions are clearly observed, delimited by two discontinuities in the pressure dependence of the faujasite volume around 2 and 3.5 GPa. The transition from the crystal to the amorphous state is incomplete and partially reversible below pressures of between 8 and 12 GPa, depending on the pressure-transmitting medium used. This partial recovery of the initial structure, at least on a local level, could be related to the presence of hydrated sodium ions in the faujasite framework. In addition, the position of the first sharp diffraction peak in the X-ray diffraction pattern of a fully amorphous sample recovered from 24 GPa is consistent with the presence of 4-membered rings of tetrahedra and the persistence of a significant number of larger rings as compared to a dried amorphous faujasite precursor.