Pressure-induced Polyamorphism in CaAl<sub>2</sub>O<sub>4</sub> Glass Revealed by <i>in situ</i> Experiments using Synchrotron X-ray

In situ high-pressure sound velocity measurements of CaAl2O4 glass demonstrated irreversible discontinuities in the sound velocities at ~8–10 GPa. In situ high-pressure synchrotron x-ray diffraction measurements showed an intermediate-range structure change attributed to a rearrangement of calcium ions over this narrow pressure region. Atomistic models obtained from molecular dynamics simulations revealed that this structure change originates from a transition from a bimodal Ca-O void radius distribution including voids larger than ~2.4 Å to a unimodal distribution without the large voids.