Pressure-induced metastable phase transition in orthoenstatite (MgSiO3) at room temperature: a Raman spectroscopic study

摘要

Phase behavior of a synthetic orthoenstatite in a diamond-anvil cell has been studied up to similar to22GPa by using Raman spectroscopy at room temperature. Under quasi-hydrostatic conditions, orthoenstatite undergoes a reversible phase transformation at an apparent transition pressure of similar to 10 GPa for compression and similar to9.5 GPa for decompression. The 3d transition-metal cations, e.g., Fe2+ and Ni2+, show only a minor effect on the transition pressure within 10wt% of addition. All the Raman frequencies in both orthoenstatite and its high-pressure phase increase monotonically with increasing pressure. The amount of forward or backward transition is fixed at a given pressure and forms a hysteresis loop in the transition %-pressure plan. The type for the present metastable phase transition is inferred to be of first order and the high-pressure polymorph may be the intermediate between orthoenstatite and the high-pressure clinoenstatite (i.e., the high-P C2/c phase). A mechanism based on Mnyukh's edgewise model of interface motion has been suggested to account for the observed phenomena. (C) 2003 Elsevier Inc. All rights reserved. [References: 34]