A High-Pressure Brillouin and Raman Scattering Study on Na2FeSi3O8.5 Glass: Implications for Pressure-induced Shear Velocity Minima in Silicate Glasses

Sound velocities of Na2FeSi3O8.5 glass have been measured to 12 GPa by Brillouin spectroscopy. Poisson's ratio and bulk, shear, and Young's moduli are calculated as a function of pressure. The shear and Young's moduli and Poisson's ratio show a shift in the response to compression of the glass at ∼2.2 GPa, where the pressure dependence of the shear modulus reverses sign. This shift mirrors those of a wide suite of glasses, and further demonstrates that pressure-induced shear velocity minima are general phenomena in silicate glasses containing few network modifiers. Raman spectra have also been collected of the glass up to 6.5 GPa. A relation is proposed between the magnitude of shear velocity depression observed under pressure in silicate glasses and the ratio of the number of network-modifying cations and network-forming cations. This relation can prospectively be deployed to compositionally tailor the pressure dependence of the elastic velocities of silicate glasses.