A high pressure Brillouin scattering study of vitreous boron oxide up to 57 GPa

Brillouin spectroscopy has been performed on vitreous boron oxide (B2O3) from ambient pressure to 57 GPa at room temperature. Upon initial compression to 53 GPa, the longitudinal and shear sound velocities increase gradually from 3.3 km/s to 13.1 km/s and from 1.8 km/s to 7.1 km/s respectively. Upon decompression, the shear and longitudinal sound velocities follow a different path than during compression. This path remains smooth until a discontinuity of approximately 2.7 km/s in the longitudinal velocity and 2.0 km/s in the shear velocity occurs near 2.8 GPa. This discontinuity returns the sound velocities to those seen during compression, and suggests a polyamorphic reorganization of the glass structure. The path dependent nature of the properties and the discontinuity at 2.8 GPa can also be seen in the Poisson’s ratio and the index of refraction. A second compression–decompression cycle to 57 GPa produces the same behavior as the first cycle, confirming that the 2.8 GPa discontinuity does in fact return the glass to its original structure. The existence of a sharp transition in glass properties, such as was observed here, provides strong support for the existence of vitreous polymorphs.