High pressure Raman spectra of β-Mg 2SiO 4, γ-Mg 2SiO 4, MgSiO 3-ilmenite and MgSiO 3-perovskite

Abstract

The Raman spectra of polycrystalline β-Mg 2SiO 4, MgSiO 3-ilmenite and MgSiO 3-perovskite and single crystals of γ-Mg 2SiO 4 immersed in either H 2O or a methanol-ethanol mixture were measured inside a diamond-anvil cell at room temperature up to pressures as high as 0.5 Mbar. With the exception of MgSiO 3-perovskite, all these phases were investigated at pressures beyond their respective stability fields. Except for some weak Raman bands, which were not well determined at high pressures, the Raman frequencies of all four phases were observed to vary nonlinearly with pressure. The data for γ-Mg 2SiO 4 and MgSiO 3-ilmenite at high pressures are believed to be the first reported in the literature. This study failed to find any evidence of the so-called “second” order phase transition in β-Mg 2SiO 4 at high pressures and room temperature which was reported in a previous Raman study. The data of MgSiO 3-perovskite are generally in good agreement with previously published results.