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Application of Landau theory to cation ordering in omphacite; 2, Kinetic behaviour

M. A. Carpenter, M. C. Domeneghetti and V. Tazzoli
Application of Landau theory to cation ordering in omphacite; 2, Kinetic behaviour
European Journal of Mineralogy (February 1990) 2 (1): 19-28

Abstract

The kinematics of cation disordering have been followed in single- crystals of omphacite which were annealed in evacuated silica tubes at 900, 950 and 1000 degrees C. The X-ray intensities I (sub k) , of superlattice reflections were used to monitor changes in the macroscopic order parameter, Q, with annealing time (I (sub k) alpha Q (super 2) ). A purely empirical analysis of the kinetic data gives a rate law of the form ln(Q (super 2) ) alpha t (super 1/2) and an enthalpy of activation of 615 +- 65 kJ/mole. The data are also approximately described by Q (super 2) alpha ln t for a range of t. Time-dependent order parameter theory provides a more rigorous basis for analysing the disordering transition and the data have been compared with a specific solution of the Ginzburg-Landau equation. This analysis gives an example of how Landau theory for equilibrium behaviour can be coupled with the Ginzburg-Landau equation for kinetics to describe structural phase transitions in minerals under non-equilibrium conditions.


ISSN: 0935-1221
Serial Title: European Journal of Mineralogy
Serial Volume: 2
Serial Issue: 1
Title: Application of Landau theory to cation ordering in omphacite; 2, Kinetic behaviour
Affiliation: Univ. Cambridge, Dep. Earth Sci., Cambridge CB2 3EQ, United Kingdom
Pages: 19-28
Published: 199002
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 19
Accession Number: 1992-062495
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: 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: 1992
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