Nature Communications (Sep 2024)

Phase transition kinetics of superionic H2O ice phases revealed by Megahertz X-ray free-electron laser-heating experiments

  • R. J. Husband,
  • H. P. Liermann,
  • J. D. McHardy,
  • R. S. McWilliams,
  • A. F. Goncharov,
  • V. B. Prakapenka,
  • E. Edmund,
  • S. Chariton,
  • Z. Konôpková,
  • C. Strohm,
  • C. Sanchez-Valle,
  • M. Frost,
  • L. Andriambariarijaona,
  • K. Appel,
  • C. Baehtz,
  • O. B. Ball,
  • R. Briggs,
  • J. Buchen,
  • V. Cerantola,
  • J. Choi,
  • A. L. Coleman,
  • H. Cynn,
  • A. Dwivedi,
  • H. Graafsma,
  • H. Hwang,
  • E. Koemets,
  • T. Laurus,
  • Y. Lee,
  • X. Li,
  • H. Marquardt,
  • A. Mondal,
  • M. Nakatsutsumi,
  • S. Ninet,
  • E. Pace,
  • C. Pepin,
  • C. Prescher,
  • S. Stern,
  • J. Sztuk-Dambietz,
  • U. Zastrau,
  • M. I. McMahon

DOI
https://doi.org/10.1038/s41467-024-52505-0
Journal volume & issue
Vol. 15, no. 1
pp. 1 – 13

Abstract

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Abstract H2O transforms to two forms of superionic (SI) ice at high pressures and temperatures, which contain highly mobile protons within a solid oxygen sublattice. Yet the stability field of both phases remains debated. Here, we present the results of an ultrafast X-ray heating study utilizing MHz pulse trains produced by the European X-ray Free Electron Laser to create high temperature states of H2O, which were probed using X-ray diffraction during dynamic cooling. We confirm an isostructural transition during heating in the 26-69 GPa range, consistent with the formation of SI-bcc. In contrast to prior work, SI-fcc was observed exclusively above ~50 GPa, despite evidence of melting at lower pressures. The absence of SI-fcc in lower pressure runs is attributed to short heating timescales and the pressure-temperature path induced by the pump-probe heating scheme in which H2O was heated above its melting temperature before the observation of quenched crystalline states, based on the earlier theoretical prediction that SI-bcc nucleates more readily from the fluid than SI-fcc. Our results may have implications for the stability of SI phases in ice-rich planets, for example during dynamic freezing, where the preferential crystallization of SI-bcc may result in distinct physical properties across mantle ice layers.