Thermodynamics of plagioclase III: Spontaneous strain at the {Mathematical expression} phase transition in Ca-rich plagioclase

Simon A.T. Redfern; Ann Graeme-Barber; Ekhard Salje

doi:10.1007/BF00203199

Thermodynamics of plagioclase III: Spontaneous strain at the {Mathematical expression} phase transition in Ca-rich plagioclase

Simon A.T. Redfern^*, Ann Graeme-Barber, Ekhard Salje

^*Corresponding author for this work

University of Cambridge

Research output: Contribution to journal › Article › peer-review

38 Citations (Scopus)

Abstract

The lattice parameters of anorthites An₉₈Ab₂ and An₁₀₀ have been measured from 22 to 1100 K. The spontaneous strain arising from the {Mathematical expression} displacive transition in An₉₈ follows second order Landau behaviour. The spontaneous strain (e{open}_s) couples quadratically to the order parameter (Q⁰) with e{open}_s∝Q⁰²∝(T_c^*-T) and T_c^*=530 K in An₉₈. This is in contrast to the tricritical behaviour observed in pure anorthite. These observations are consistent with a Landau model for the free energy of Ca-rich plagioclases in which Al/Si order and Na content renormalize the fourth order coefficient.

Original language	English
Pages (from-to)	157-163
Number of pages	7
Journal	Physics and Chemistry of Minerals
Volume	16
Issue number	2
DOIs	https://doi.org/10.1007/BF00203199
Publication status	Published - Nov 1988
Externally published	Yes

ASJC Scopus Subject Areas

General Materials Science
Geochemistry and Petrology

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T2 - Spontaneous strain at the {Mathematical expression} phase transition in Ca-rich plagioclase

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AU - Graeme-Barber, Ann

AU - Salje, Ekhard

PY - 1988/11

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N2 - The lattice parameters of anorthites An98Ab2 and An100 have been measured from 22 to 1100 K. The spontaneous strain arising from the {Mathematical expression} displacive transition in An98 follows second order Landau behaviour. The spontaneous strain (e{open}s) couples quadratically to the order parameter (Q0) with e{open}s∝Q02∝(Tc*-T) and Tc*=530 K in An98. This is in contrast to the tricritical behaviour observed in pure anorthite. These observations are consistent with a Landau model for the free energy of Ca-rich plagioclases in which Al/Si order and Na content renormalize the fourth order coefficient.

AB - The lattice parameters of anorthites An98Ab2 and An100 have been measured from 22 to 1100 K. The spontaneous strain arising from the {Mathematical expression} displacive transition in An98 follows second order Landau behaviour. The spontaneous strain (e{open}s) couples quadratically to the order parameter (Q0) with e{open}s∝Q02∝(Tc*-T) and Tc*=530 K in An98. This is in contrast to the tricritical behaviour observed in pure anorthite. These observations are consistent with a Landau model for the free energy of Ca-rich plagioclases in which Al/Si order and Na content renormalize the fourth order coefficient.

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Thermodynamics of plagioclase III: Spontaneous strain at the {Mathematical expression} phase transition in Ca-rich plagioclase

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