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Phase transitions in perovskites near the tricritical point: an experimental study of KMn1–xCaxF3 and SrTiO3

Published online by Cambridge University Press:  05 July 2018

M. C. Gallardo ,
F. J. Romero ,
S. A. Hayward ,
E. K. H. Salje  and
J. del Cerro
M. C. Gallardo*
Affiliation:
Departamento de Física de la Materia Condensada, Universidad de Sevilla, PO Box 1065, E-41080 Sevilla, Spain
F. J. Romero
Affiliation:
Departamento de Física de la Materia Condensada, Universidad de Sevilla, PO Box 1065, E-41080 Sevilla, Spain
S. A. Hayward
Affiliation:
Departamento de Física de la Materia Condensada, Universidad de Sevilla, PO Box 1065, E-41080 Sevilla, Spain
E. K. H. Salje
Affiliation:
Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK
J. del Cerro
Affiliation:
Departamento de Física de la Materia Condensada, Universidad de Sevilla, PO Box 1065, E-41080 Sevilla, Spain
*
*E-mail: [email protected]
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Abstract

We present experimental data for the Pm3m-I4/mcm phase transitions in the perovskite crystals KMn1-xCaxF3 and SrTiO3. Comparison of calorimetric data (latent heat and specific heat) with order parameter data (measured with X-ray rocking methods) indicates that these transitions follow mean-field behaviour, and may be described using Landau potentials where the free energy expansion includes terms up to Q6. This potential is characteristic of transitions close to the tricritical point. Comparison of the behaviour of SrTiO3 and KMnF3 indicates that KMnF3 is closer to the tricritical point; a small amount of substitution of Ca for Mn causes the transition to cross the tricritical point from first order to second order behaviour.

Keywords

phase transitionperovskitetricritical pointLandau theory
Type
Research Article
Information
Mineralogical Magazine , Volume 64 , Issue 6 , December 2000 , pp. 971 - 982
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2000

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