Pressure-driven symmetry transitions in dense H2 O ice

Abstract

X-ray diffraction and Raman spectroscopy of H2O (ice) structures are measured under static compression in combination with grain normalizing heat treatment via direct laser heating. We report the transition from cubic ice-VII to a structure of tetragonal symmetry, ice-VIIt at 5.1±0.5GPa. This is succeeded by the H-bond symmetrization transition occurring at a pressure of 30.9±3GPa. Both experimental observations are supported by simulated Raman spectra from density-functional theory quantum calculations. The transition to H-bond symmetrization is evidenced by the reversible emergence of its characteristic Raman mode and a 2.5-fold increase in bulk modulus, implying a significant increase in bonding strength. © 2022 American Physical Society.