Structural changes in CaSiO3 glass up to lower mantle pressures

The physical properties of silicate melts at temperature and pressure conditions of the Earth’s mantle have a fundamental influence on the chemical and thermal evolution of the Earth. However, direct investigations of melt structures at these conditions are experimentally very difficult or even impossible with current capabilities. To still be able to obtain an estimate of the structural behavior of melts at high pressures and temperatures, amorphous materials have been widely used as analogue materials.

Here we present the structural response of CaSiO₃ glass as a proxy for deep mantle melts up to 108 GPa via total X-ray scattering experiments. The measurements were carried out at beamline P02.2 at DESY, Germany, utilizing the newly commissioned Soller Slit configuration. Due to the pronounced size contrast between Ca²⁺ and Si⁴⁺, the Si–O correlations are readily resolved in the pair‐distribution function—something that is impossible in other three component silicate glasses, like MgSiO₃ where the Mg–O and Si–O peaks overlap at a larger pressure.

We observe smooth pressure-induced changes in the structure factor and pair distribution function, along with a clear increase in Si–O coordination from four-fold to six-fold within the first 50 GPa. This behavior will be examined in detail, with emphasis on mechanistic differences relative to pure SiO₂ and in comparison with other reported results for silicate glasses under similar pressure conditions.