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An EXAFS study of cation site distortions through the P2/c-P1̄ phase transition in the synthetic cuproscheelite-sanmartinite solid solution

Published online by Cambridge University Press:  05 July 2018

P. F. Schofield ,
J. M. Charnock ,
G. Cressey  and
C. M. B. Henderson
P. F. Schofield
Affiliation:
Department of Geology, University of Manchester, Oxford Road, Manchester M13 9PL, UK
J. M. Charnock
Affiliation:
Department of Geology, University of Manchester, Oxford Road, Manchester M13 9PL, UK
G. Cressey
Affiliation:
Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK
C. M. B. Henderson
Affiliation:
Department of Geology, University of Manchester, Oxford Road, Manchester M13 9PL, UK
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Abstract

EXAFS spectroscopy has been used to monitor changes in divalent cation site geometries across the P2/c-P1̄ phase transition in the sanmartinite (ZnWO4)-cuproscheelite (CuWO4) solid solution at ambient and liquid nitrogen temperatures. In the ZnWO4 end member, Zn occupies axially-compressed ZnO6 octahedra with two axial Zn-O bonds at approximately 1.95 Å and four square planar Zn-O bonds at approximately 2.11 Å. The substitution of Zn by Cu generates a second Zn environment with four short square planar Zn-O bonds and two longer axial Zn-O bonds. The proportion of the latter site increases progressively as the Cu content increases. Cu EXAFS reveals that the CuO6 octahedra maintain their Jahn-Teller axially-elongate geometry throughout the majority of the solid solution and only occur as axially-compressed octahedra well within the stability field of the Zn-rich phase with monoclinic long-range order.

Keywords

EXAFS spectroscopysanmartinitecuproscheelitephase transition
Type
Experimental Mineralogy
Information
Mineralogical Magazine , Volume 58 , Issue 391 , June 1994 , pp. 185 - 199
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1994

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Footnotes

*

Present Address: Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK

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