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

Michail N. Taran 1 , Fabrizio Nestola 2 , Haruo Ohashi 3 , Monika Koch-Müller 4 , Tonci Balic-Zunic 5  and Lars Arnskov Olsen 5
  • 1 Institute of Geochemistry, Mineralogy and Ore Formation, National Academy of Sciences of Ukraine, Paladin Avenue 34, 03680 Kyiv-142, Ukraine
  • 2 Dipartimento di Geoscienze, Università di Padova, Corso Garibaldi 37, I-35137 Padova, Italy
  • 3 HASHI Institute for Silicate Science, Nishinakanobu 1-9-25, Shinagawa, Tokyo 142-0054, Japan
  • 4 GeoForschungsZentrum, Sektion 4.1, Telegrafenberg, 14473 Potsdam, Germany
  • 5 Geological Institute, University of Copenhagen, Øster Voldgade 10, 1350 Copenhagen K, Denmark

Abstract

The pressure-induced behavior of spin-allowed dd-bands of VIIICo2+ in the absorption spectra of synthetic Co3Al2Si3O12 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 CoO8 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 Co3Al2Si3O12.

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