Raman study of 3.65 Å-phase MgSi(OH)₆ under high pressure and the bands assignment

ABSTRACT

3.65 Å-phase (or hydroxide-perovskite), MgSi(OH)₆, is a representative of dense hydrous magnesium silicates (DHMS) with maximum water content (up to ∼35 wt.% H₂O) and thus is of interest as one of the largest repositories of water among all the known hydrous phases. Sample of 3.65 Å-phase, grown in DIA-type multianvil apparatus, was studied by Raman spectroscopy under pressure up to ∼7 GPa with diamond anvil cell. Interpretation of the Raman spectrum was carried out using lattice-dynamical simulations within ab initio DFT method (CASTEP code). Additionally, OH-stretching bands are analyzed with two phenomenological models: empirical model by Novak and Libowitzky, using correlation between O–O distance and the wavenumber of the OH-stretching band, and theoretical model, using double Morse potentials of hydrogen bond O–H···O. Upon the pressure increase, octahedral and bending δ(ОН) vibrations exhibit linear positive pressure shift, whereas wavenumbers of the ОН-stretching modes show inverse pressure dependence.

KEYWORDS:

• 3.65 Å-phase
• dense hydrous magnesium silicates
• Raman spectra
• high pressure
• six-coordinated silicon

Acknowledgements

This work was supported by the Russian Federation state assignment of Institute of Geology and Mineralogy of SB RAS and Institute of Physics of Federal Research Center KSC SB RAS and the Russian Foundation for Basic Research (Grant No. 18-05-00966).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the Russian Federation state assignment of Institute of Geology and Mineralogy of SB RAS and Institute of Physics of Federal Research Center KSC SB RAS and the Russian Foundation for Basic Research [grant number 18-05-00966].