Abstract
Brillouin experiments on vitreous yttrium-phosphate glass under pressures up to 7GPa obtained using a diamond anvil cell are reported. Irreversible changes occur as a function of pressure and are interpreted as an indication of a new polymorph of the original glass. The results are compared with the experimental data available for a series of different glassy systems. The observed Brillouin frequency shift under pressure relative to longitudinal waves is assigned to a rearrangement of PO4 tetrahedra. A mechanism accounting for the pressure-induced transition in glasses is proposed.