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Temperature dependence of the cation distribution in CoAl (sub 2) O (sub 4) spinel

Hugh St. C. O'Neill
Temperature dependence of the cation distribution in CoAl (sub 2) O (sub 4) spinel
European Journal of Mineralogy (October 1994) 6 (5): 603-609

Abstract

The cation distribution in synthetic CoAl (sub 2) O (sub 4) was determined, in samples quenched from 750-1200 degrees C, by Rietveld structure refinement of XRD data. The inversion parameter, x, increases smoothly from 0.11 at 750 to 0.25 (+ or - 0.005) at 1200 degrees C, and can be described by a conventional thermodynamic model, with alpha (super Co-Al) = 45.3 + or - 0.5 and beta = -18.3 + or - 1.2 kJ/mol. Since Co (super 2+) and Fe (super 2+) usually show similar high-T crystal-chemical behaviour, the present results emphasize the anomalous nature of recent results for the T-dependence of cation distribution in FeAl (sub 2) O (sub 4) , which could not be reasonably fitted to the usual thermodynamic model. This apparently anomalous behaviour of FeAl (sub 2) O (sub 4) may be an artefact of unusually fast rate of cation re-ordering in FeAl (sub 2) O (sub 4) due to intrinsic Fe (super 3+) /vacancy defects.


ISSN: 0935-1221
Serial Title: European Journal of Mineralogy
Serial Volume: 6
Serial Issue: 5
Title: Temperature dependence of the cation distribution in CoAl (sub 2) O (sub 4) spinel
Affiliation: Universitaet Bayreuth, Bayerisches Geoinstitut, Bayreuth, Federal Republic of Germany
Pages: 603-609
Published: 199410
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 13
Accession Number: 1994-054178
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United KingdomTwickenhamUKUnited Kingdom
Update Code: 199424
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