Raman Spectrum of Calcium Carbonate at High Pressures

Abstract
Raman spectra of calcite, CaCO3 II, and CaCO3 III have been studied at various pressures as high as 40 kbar. Thirteen lines have been observed in the previously unreported spectrum of CaCO3 II and 20 lines are reported for the CaCO3 III spectrum. These spectra are compared with Raman spectra of aragonite, KNO3 III, and KNO3 IV; and previous suggestions that CaCO3 II and KNO3 III may be isostructural and that CaCO3 III and KNO3 IV also may be isostructural are shown to be incorrect. Alternative structures for CaCO3 II and CaCO3 III are briefly considered.

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