Phase transitions and Raman spectra of calcite at high pressures and room temperature

Abstract

Calcite displays two reversible phase transformations at high pressures and room temperature. We found, however, that transformation to calcite-II is more likely to occur under nonhydrostatic conditions. This means that it is difficult to locate the transition pressure between calcite-I and calcite-II in a hydrostatic environment. Calcite-III was always found to exist at pressures above 20 kbar at room temperature. It was often observed that calcite-I transformed directly to calcite-III with increasing pressure and that calcite-III always reverted directly to calcite-I with decreasing pressure, without the appearance of calcite-II in either case. The Raman spectra of both calcite-I and calcite-II and the effect of pressure on the spectra of these phases observed in the present study are consistent with those of earlier investigations. -from Authors Show more