Vibrational spectroscopy at very high pressures. Part 26. An infrared study of the metastable phases of Ca[CO3]

Abstract

Infrared and far-i.r. spectra of Ca[CO₃] have been recorded under hydrostatic conditions in a diamond anvil cell to 40 kbar. The new data are analysed in conjuction with the Raman results of Fong and Nicol. The spectra of Ca[CO₃](II) are shown to be consistent with a recent X-ray single-crystal structure, with site rather than factor-group selection rules accounting for most features. For Ca[CO₃](III) a structure is postulated in which there are two crystallographically-distinct sets of anions in a primitive cell with Z being at least four and probably eight.