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

Abstract

Recent structural study of the high-pressure Zn 2 SiO 4 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 highpressure 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.

High-pressure phase relations in Zn2SiO4 system: A first-principles study

“…As noted before, phases III and IV are "experimentally" observed at a pressure range between 8 to 11 GPa in the recovered samples [1]. In-situ Raman spectroscopic study [11] has demonstrated that phases III and IV transformed to the structure-unknown high-pressure phases (III-HP and IV-HP) at 5.5 and 2.5 GPa during compression, respectively. Therefore, there must be two stable phases corresponding those phases between phases II and V. However, no lowest enthalpy phases other than phase V were detected at pressure corresponding to synthesis of phases III and IV (8 to 11 GPa).…”

“…These two phases show very similar compressional behaviors (Figure 1). Kanzaki [11] observed a phase transition of phase III to III-HP at 5.5 GPa during compression. So natural question is that phase III-Pbam corresponds to phase III-HP?…”

“…Recent in-situ high-pressure Raman spectroscopic study of phases III and IV at room temperature revealed that both phases exhibited the pressure-induced phase transitions at 5.5 and 2.5 GPa during compression, respectively [11]. These transformed phases are abbreviated as III-HP and IV-HP hereafter to avoid confusion.…”