Nature of the molecular-to-atomic transition in liquid silica at extreme conditions

Molecular-to-atomic transitions are often associated with changes in structural and transport properties and can have profound implications for different areas in high-energy-density (HED) and planetary sciences. SiO₂ (silica) under extremely high pressures and temperatures is often encountered in HED experiments and is an important building block of planets. The molecular-to-atomic transition in liquid silica has been suggested by previous studies but the mechanism of the transition has not been fully understood, experimentally and theoretically. We have performed comprehensive first-principles calculations that combine analysis of the thermodynamic, structural, and electronic properties during the transition. Our calculated Hugoniots show good consistency with well-established experimental data. We have also found clear signatures of chemical bond dissociation during the transition and large sensitivity of the transition temperature to pressure. These results reconcile previous experiments¹ and theories² by providing direct evidence and clarification about the nature of this process important for HED and planetary sciences.

1. D. G. Hicks et al., Phys. Rev. Lett. 97, 025502 (2006).

2. R. Scipioni et al., Proc. Natl. Acad. Sci. USA 114, 9009 (2017).