CaSiO3 Glass Under Pressure: Structural Evolution, Elastic Response, and Comparison with MgSiO3 and SiO2 Glasses

Abstract

We have studied CaSiO3 glass to 65 GPa using synchrotron X-ray scattering, Raman spectroscopy, and Brillouin scattering to investigate its structural and elastic evolution. X-ray scattering reveals the emergence of a new feature in the pair distribution function, g(r), near 3 Å from ∼5 GPa and a systematic shift in the first sharp diffraction peak (FSDP), attributed to a progressive collapse of medium-range order. Raman spectra show discrete amorphous-amorphous structural modifications near ∼2, ∼5, and ∼22 GPa, as evidenced by the reduction of Q0 species, the redistribution toward Q1 and Q2 species, the formation of dense three-membered rings, and the development of SiO5 and SiO6 units. The Si coordination number increases from ∼4 in ambient conditions to ∼6 above ∼40 GPa. At the same time, the Ca coordination number increases to nearly 8. Brillouin measurements indicate continuous elastic stiffening with pressure, consistent with progressive densification and coordination increase in the Ca-rich depolymerized network. These results provide a better understanding of the role of modifier cations in controlling structural evolution and elastic properties. The observed behavior in CaSiO3 glass is compared with that in MgSiO3 and SiO2 glasses, revealing that modifier cations exert first-order control over polymerization pathways, medium-range collapse, coordination increase, and elastic anomalies in supercooled depolymerized silicate melts.