Crystal Structure of Symmetric Ice X in H2O–H2 and H2O–He under Pressure

• Published in: The journal of physical chemistry letters Vol. 12; no. 19; pp. 4707 - 4712
• Main Authors: Lei, Jialin, Lim, Jinhyuk, Kim, Minseob, Yoo, Choong-Shik
• Format: Journal Article
• Language: English
• Published: American Chemical Society 20.05.2021
• Subjects: Physical Insights into Materials and Molecular Properties
• ISSN: 1948-7185; 1948-7185
• DOI: 10.1021/acs.jpclett.1c00606

Ice VII and ice X are the two most dominant phases, stable over a large pressure range between 2 and 150 GPa and made of fundamentally different chemical bonding. Yet, the two ice phases share a similar bcc-based crystal structure and lattice constants, resulting in a challenge to discern the crystal structure of ice VII and ice X. Here, we present well-resolved X-ray diffraction data of H2O in quasi-hydrostatic H2 and He pressure media, clearly resolving the two ice phases to 130 GPa and the dissociative nature of ice VII to X transition occurring at 20–50 GPa in H2O–H2 and 60–70 GPa in H2O–He. The present diffraction data permits, for the first time, the accurate determination of the bulk moduli B 0 of 225 (or 228) GPa for ice X and 6.2 (or 4.5) GPa for ice VII, in H2O–H2 (or H2O–He), which can provide new constraints for Giant planetary models.