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Structural changes induced by cation ordering in ferrotapiolite

Published online by Cambridge University Press:  05 July 2018

M. Zema ,
S.C. Tarantino  and
A. Giorgiani
M. Zema*
Affiliation:
Dipartimento di Scienze della Terra, Università di Pavia, Via Ferrata 1, 27100 Pavia, Italy
S.C. Tarantino
Affiliation:
Dipartimento di Scienze della Terra, Università di Pavia, Via Ferrata 1, 27100 Pavia, Italy
A. Giorgiani
Affiliation:
Dipartimento di Scienze della Terra, Università di Pavia, Via Ferrata 1, 27100 Pavia, Italy
*
*E-mail: [email protected]
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Abstract

Structural modifications as a function of the degree of order (Q) in FeTa2O6 ferrotapiolite have been characterized by means of single-crystal X-ray diffraction (SC-XRD). A total of 26 datasets covering the range of Q between 0.154 and 1 have been obtained by thermal treatments followed by quenching of natural tapiolite crystals. Ordering of Fe2+ at the A sites and of Ta5+ at the B sites causes a linear increase in the a/c lattice constants ratio, as a consequence of a linear decrease of the c dimension and only slight modifications of the a parameter. Calibration of a/c vs. Q represents a very useful tool for a rapid determination of the degree of order of tapiolite samples. Polyhedral volumes of the two octahedral sites vary linearly with Q as a consequence of the different ionic radii of the two species. Both the sites remain almost regular at all Q values but the B site shows an increasing off-centre displacement of the cation with increasing Q. Observed structure factors of supercell reflections, characterized by l ≠ 3n, increase linearly as a function of Q, thus representing a further tool for a quick evaluation of the degree of order.

Keywords

tapioliteorder-disordersingle-crystal X-ray diffraction
Type
Research Article
Information
Mineralogical Magazine , Volume 70 , Issue 3 , June 2006 , pp. 319 - 328
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2006

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