Pressure–induced phase transitions of Zn₂SiO₄ III and IV studied using in–situ Raman spectroscopy

Abstract

Recent structural study of the high–pressure Zn₂SiO₄ phases III and IV has suggested that they are retrograde phases formed during decompression. To clarify the stabilities of these phases under pressure, in–situ high–pressure Raman spectroscopic measurements were taken at room temperature. Phase III, having a ‘tetrahedral olivine’ structure, transformed to a new phase at 5.5 GPa during compression and returned to phase III at 1.7 GPa during decompression. Phase IV also exhibited a phase transition at 2.5 GPa with very small hysteresis. Both transitions are first–order. These observations confirmed that phases III and IV are retrograde phases.