Investigation of polyamorphism in compressed $\mathrm{В_2О_3}$ glass by the direct measurement of the density

Precise measurements of the relative volume change of vitreous B₂O₃ have been performed by the strain-gauge technique at hydrostatic pressures up to 9 GPa. The features of the strain-gauge technique are analyzed and the specificity of the measurements of “relaxed” and “unrelaxed” bulk moduli is discussed. Smeared anomalies of compressibility (at P > 0.5 GPa and P > 5 GPa) and logarithmic relaxation of the glass density are observed. A significant (by several times!) difference has been revealed between the relaxed bulk modulus of glass obtained from the volume measurements and the unrelaxed modulus estimated from the Brillouin spectroscopic data. The measurements of the relative volume change under compression together with the previous structure investigations and computer simulation results reveal the basic features of the phase transitions in B₂O₃ glass. Both direct and reverse transitions are smeared in pressure. The residual densification in glass is not associated with change in the short-range order.