^1,2Xiaojing Lai,³Feng Zhu,²Dongzhou Zhang,⁴Sergey Tkachev,⁴Vitali B. Prakapenka,²Keng-Hsien Chao,²Bin Chen
American Mineralogist 108, 1530-1537 Link to Article [http://www.minsocam.org/msa/ammin/toc/2023/Abstracts/AM108P1530.pdf]
¹Gemmological Institute, State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan, Hubei, 430074, China 
²Hawaii Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, Honolulu, Hawaii 96822, U.S.A. 
³School of Earth Sciences, State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan, Hubei, 430074, China 
⁴Center for Advanced Radiation Sources, University of Chicago, Chicago, Illinois 60637, U.S.A.
Copyright: The Mineralogical Society of America

Ice-VII is a high-pressure polymorph of H2O ice and an important mineral widely present in many
planetary environments, such as in the interiors of large icy planetary bodies, within some cold subducted
slabs, and in diamonds of deep origin as mineral inclusions. However, its stability at high pressures
and high temperatures and thermoelastic properties are still under debate. In this study, we synthesized
ice-VII single crystals in externally heated diamond-anvil cells and conducted single-crystal X-ray
diffraction experiments up to 78 GPa and 1000 K to revisit the high-pressure and high-temperature
phase stability and thermoelastic properties of ice-VII. No obvious unit-cell volume discontinuity or
strain anomaly of the high-pressure ice was observed up to the highest achieved pressures and temperatures. The volume-pressure-temperature data were fitted to a high-temperature Birch-Murnaghan
equation of state formalism, yielding bulk modulus KT0 = 21.0(4) GPa, its first pressure derivative KT′0
= 4.45(6), dK/dT = –0.009(4) GPa/K, and thermal expansion relation αT = 15(5) × 10–5 + 15(8) × 10–8
× (T – 300) K–1. The determined phase stability and thermoelastic properties of ice-VII can be used to
model the inner structure of icy cosmic bodies. Combined with the thermoelastic properties of diamonds,
we can reconstruct the isomeke P-T paths of ice-VII inclusions in diamond from depth, offering clues
on the water-rich regions in Earth’s deep mantle and the formation environments of those diamonds.