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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*
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
*

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 Q 6. 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.

Information

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2000

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