Site occupancy of Co and Ni in erythrite-annabergite solid solutions deduced by vibrational spectroscopy

Martens, Wayde N., Kloprogge, J. Theo, Frost, Ray L., & Rintoul, Llew (2005) Site occupancy of Co and Ni in erythrite-annabergite solid solutions deduced by vibrational spectroscopy. The Canadian Mineralogist, 43(3), pp. 1065-1075.

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Abstract

Members of the solid-solutions series between erythrite [Co3(AsO4)2.8H2O] and annabergite [Ni3(AsO4)2.8H2O] were synthesized and studied by a combination of X-ray diffraction, scanning electron microscopy, and Raman and infrared spectroscopy. The solid solution is complete, with the monoclinic C2/m space group being retained throughout. The unit-cell parameters decrease in size along all crystallographic directions as the amount of Ni increases. The β angle in the unit cell also decreases from 105.05(1) ° (erythrite) to 104.90(1) ° (annabergite). Crystals of annabergite and samples with high Ni content elongate along the a axis, contrasting with crystals of erythrite and Co-rich samples, which elongate along c. In the Raman and infrared spectra of the synthetic minerals, the band positions shift in accordance with the increase in bond strength associated with the decrease in the unit-cell parameters. Trends in Raman band positions of the antisymmetric arsenate stretching vibrations are sensitive to the site occupancy of metal ions in the crystal structure. Changes in the crystal morphology, unit-cell parameters and vibrational spectra have been rationalized in terms of the site occupancy of Co and Ni in the crystal structure. Substitution of Ni is directed to metal site 1 (C2h site symmetry) whereas Co is directed to metal site 2 (C2 site symmetry). Raman spectroscopy has proved to be useful for the determination of site occupancy of metal ions in solid solutions of minerals.

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ID Code: 1892
Item Type: Journal Article
Refereed: Yes
Additional URLs:
Keywords: erythrite, annabergite, cobalt arsenate, nickel arsenate, solid solution, Raman spectroscopy, vivianite group minerals, Infrared spectroscopy
ISSN: 1499-1276
Divisions: Past > QUT Faculties & Divisions > Faculty of Science and Technology
Copyright Owner: Copyright 2005 Mineralogical Association of Canada
Copyright Statement: Reproduced in accordance with the copyright policy of the publisher.
Deposited On: 26 Jul 2005 00:00
Last Modified: 25 Feb 2013 03:53

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