Self-diffusion of protons in H2O ice VII at high pressures: Anomaly around 10 GPa

Naoki Noguchi, Takuo Okuchi

Research output: Contribution to journalArticlepeer-review

13 Citations (Scopus)

Abstract

The self-diffusion of ice VII in the pressure range of 5.5-17 GPa and temperature range of 400-425 K was studied using micro Raman spectroscopy and a diamond anvil cell. The diffusion was monitored by observing the distribution of isotope tracers: D2O and H2 18O. The diffusion coefficient of hydrogen reached a maximum value around 10 GPa. It was two orders of magnitude greater at 10 GPa than at 6 GPa. Hydrogen diffusion was much faster than oxygen diffusion, which indicates that protonic diffusion is the dominant mechanism for the diffusion of hydrogen in ice VII. This mechanism is in remarkable contrast to the self-diffusion in ice Ih that is dominated by an interstitial mechanism for the whole water molecule. An anomaly around 10 GPa in ice VII indicates that the rate-determining process for the proton diffusion changes from the diffusion of ionic defects to the diffusion of rotational defects, which was suggested by proton conductivity measurements and molecular dynamics simulations.

Original languageEnglish
Article number234503
JournalJournal of Chemical Physics
Volume144
Issue number23
DOIs
Publication statusPublished - Jun 21 2016

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

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