Raman spectroscopic study of pressure-induced phase transitions in tridymite modifications

Pressure-induced phase transitions of tridymite modifications (MC, MX-1, and PO-10) were investigated by in-situ Raman spectroscopy. Starting from MC, a transition to PO-10 was observed at 0.4 GPa. At about 1.6 GPa, new Raman peaks appeared and were observed up to 8.7 GPa. This revealed a new phase, and it reverted to PO-10 at around 0.4 GPa during decompression. Contrary to previous study, PO-10 was recovered to ambient pressure. MX-1 also transformed to PO-10, and PO-10 was recovered. Starting from PO-10, the transition to the new phase was also observed but was gradual and the phase reverted to PO-10 during decompression. Present study revealed a new route to form PO-10 from MC and suggests rare PO-10 found in meteorites could be formed through this route.