We will report on direct measurements of the optical refractive indices (n_sam) of eight silicate glasses, Mg₂SiO₄, MgSiO₃, CaSiO₃, CaMgSi₂O₆ (Di), CaAlSi₂O₈ (An), NaAlSi₃O₈ (Ab), Ab₂₅An₂₅Di₅₀ and Na_0.91Al_0.89Si_2.11O₆ up to 140 GPa at room temperature. DFT computations are employeed to provide structural interpretations of the observed changes in the refractive indices. Interestingly, the relative change of refractive index with pressure (n_sam/n₀, n₀ is the index at 1 atm) is greater for glasses with higher SiO₂ and/or Al₂O₃ contents. We estimated free space ratio (FSR), which can represent the ionic packing efficiency, to interpret the relative change of refractive index with pressure, and it can be found the dependence of n_sam/n₀ on the FSR is nearly linear in a large range of SiO₂ content (~33 to 100 mol%) at P ≤ 40 GPa. Accordingly, inspired by the apparently simple relationship between the FSR and n_sam/n₀, we built an empirical model for the refractive index of silicate glasses at high pressure from their SiO₂, Al₂O₃, CaO, MgO, and Na₂O contents. In addition, relative change of bulk velocity with pressure are surveryed to explore the relationship with efficiency of ionic packing in the glass structure. These observations indicate volume-dependent physical properties of silicate glasses at high pressure (i.e. refractive index, elastic moduli, and density) are controlled by a shared fundamental mechanism rooted in the efficiency of ionic packing at ambient pressure.

Refractive index,silicate glass,high pressure,ionic packing