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

•High pressure elasticity of a soda-iron silicate glass is investigated to 12 GPa.•Elastic anomalies, including a negative pressure derivative of the shear modulus and an initially nearly pressure-independent Young's modulus, are observed on initial compression.•Pressure-induced shear velocity minima in silicate glasses are demonstrated to vary systematically with the ratio of network-modifying to network-forming cations. 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.