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Vibrational properties of -AlOOH under pressure

¹ Geodynamics Research Center, Ehime University, 2-5 Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan
² Department of Chemical Engineering and Materials Science, Minnesota Supercomputing Institute for Digital Technology and Advanced Computation, University of Minnesota, 421 Washington Avenue SE, Minneapolis, Minnesota 55455, U.S.A.

Correspondence: ^* E-mail: junt{at}sci.ehime-u.ac.jp

We have performed first-principles calculations to investigate the behavior of the hydrogen bond in -AlOOH under pressure. The highest OH-stretching A₁ and B₂ mode frequencies decrease under pressure leading to hydrogen bond symmetrization. After hydrogen bond symmetrization, the corresponding frequencies gradually increase. This softening and subsequent hardening of the OH bonds is a good spectroscopic indicator of hydrogen bond symmetrization and is observed in our GGA static calculations at ~30 GPa without considering tunneling effects. We have also carried out calculations of Raman peak intensities in several supercells with various hydrogen orderings to investigate the potential effect of H-disorder on the Raman spectrum of -AlOOH. Our results suggest that the four broad Raman bands observed experimentally in the range of OH-stretching mode frequencies could originate in H-disorder in this phase.

Key Words: Hydrogen bond • hydrous mineral • first-principles calculation • vibrational property • high pressure

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