High-pressure optical spectroscopy and X-ray diffraction studies on synthetic cobalt aluminum silicate garnet

Abstract

The pressure-induced behavior of spin-allowed dd-bands of VIII Co 2+ in the absorption spectra of synthetic Co 3 Al 2 Si 3 O 12 garnet was studied from 10 -4 to 13 GPa. The plots of the peak energy vs. pressure for the three sharpest well resolved bands at ca. 5160, 17 680, and 18 740 cm -1 display small but discernible breaks in linear relations between 4 and 5 GPa. Data from single-crystal X-ray diffraction likewise show discontinuities in trends of CoO 8 polyhedral volume and distortion, and Co-O and Si-O bond distances over this pressure range. These effects are related to a pressure-induced phase transition from the β- to α-isostructural polymorph of Co 3 Al 2 Si 3 O 12 .