The chemistry and atomistic structure of amorphous silica-based compounds under high-pressure conditions are intricately connected to numerous macroscopic properties of the Earth's mantle. To improve the understanding of their properties, detailed insights into pressure-induced structural changes in amorphous silicates is required. Among silicates, highly studied amorphous silica and alkali-earth silicates such as ${\mathrm{MgSiO}}_3$ glass have been considered as reference compounds during high-pressure studies. However, magnesium atoms have a significantly larger ionic radius compared to silicon and oxygen. Alkali-earth silicates may therefore not be suitable to study the densification behavior of amorphous silicates containing low-Z cations under pressure. In this study, we follow the pressure-induced structural changes in the partially depolymerized lithium metasilicate glass ${\mathrm{Li}}_2{\mathrm{SiO}}_3$ using x-ray Raman scattering spectroscopy at the Si ${\mathrm{L}}_{2,3}$ and O K edges as well as ab initio molecular dynamics simulations and subsequent spectrum simulations based on the Bethe-Salpeter equation. At low pressure, topological rearrangements of the Si-O network lead to an increase of its degree of polymerization. Higher-coordinated silicon and oxygen atoms gradually form at pressures above 15 GPa in contrast to the abrupt amorphous-amorphous transition in the pure parent compound ${\mathrm{SiO}}_2$. This gradual transition from ${}^{\left[4\right]}\mathrm{Si}$ to ${}^{\left[6\right]}\mathrm{Si}$ and ${}^{\left[2\right]}\mathrm{O}$ to ${}^{\left[3\right]}\mathrm{O}$ is expected to affect various macroscopic properties of alkali silicates glasses, especially those involving ion transport.

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• High-pressure studies
• Pressure effects
• Topological order
• Topological phase transition
• Amorphous materials
• Glasses
• First-principles calculations
• Raman spectroscopy
• X-ray scattering