Raman studies of pressure and temperature induced phase transformations in calcite.

摘要

Phase stability in the calcium carbonate system was investigated as a simultaneous function of pressure and temperature up to 40 kbar and several hundred degrees Kelvin using micro-Raman techniques to interrogate samples constrained within a resistively heated diamond anvil cell. Measured spectra allow unequivocal identification of crystalline phases and are used to refine the P,T phase diagram. Calcium carbonate was found to exhibit both reversible and irreversible transformation phenomena among the four known phases which exist under these conditions. Time-dependent Raman intensity variations as the material is perturbed from its equilibrium state allow real-time kinetics measurements to be performed. Evidence suggests that the order of certain observed transformations may be pressure dependent. The utility of Raman spectroscopy to follow transformation phenomena and to estimate fundamental thermophysical properties from the stress dependence of vibrational mode frequencies is demonstrated. 14 refs., 3 figs.