Strain rate effects on pressure-induced amorphous-to-amorphous transformation in fused silica

Fused silica (SiO₂ glass), a key amorphous component of Earth’s silicate minerals, undergoes coordination and phase transformations under high pressure. Although extensive studies have been conducted, discrepancies between theoretical and experimental studies remain, particularly regarding strain rate effects during compression. Here, we examine strain rate influences on the shock-induced amorphous–amorphous phase transitions in fused silica by measuring its Hugoniot equation of state and longitudinal sound velocity (C_L) up to 7 GPa at strain rates of 10⁶–10⁷ s⁻¹ using a one-stage light-gas gun. A discontinuity in the relationship between shock velocity (U_S) and particle velocity (U_P) and a significant softening in C_L of fused silica were observed near ∼ 5 GPa under shock loading. Our results indicate that high strain rates restrict Si–O–Si rotation in fused silica, modifying their bonds and increasing silicon coordination. The transition pressure by shock compression is significantly higher than that under static high-pressure conditions (2–3 GPa), which agrees with some recent theoretical predictions with high compression rates, reflecting the greater pressure needed to overcome energy barriers with the strain rate increase. These findings offer insights into strain rate-dependent phase transitions in fused silica and other silicate minerals (e.g., quartz, olivine, and forsterite), bridging gaps between theoretical simulations and experiments.