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Spontaneous strain variations through the low-temperature displacive phase transition of LiGaSi (sub 2) O (sub 6) clinopyroxene

Fernando Camara, Fabrizio Nestola, Ross J. Angel and Haruo Ohashi
Spontaneous strain variations through the low-temperature displacive phase transition of LiGaSi (sub 2) O (sub 6) clinopyroxene (in HP-HT mineral physics; implications for geosciences, Paola Comodi (prefacer), Fabrizio Nestola (prefacer) and Ross J. Angel (prefacer))
European Journal of Mineralogy (June 2009) 21 (3): 599-614

Abstract

The evolution of the lattice parameters and crystal structure of LiGaSi (sub 2) O (sub 6) clinopyroxene has been studied by single-crystal X-ray diffraction from 100 to 1073 K. Complete single-crystal X-ray diffraction data have been collected at 22 temperatures. A displacive P2 (sub 1) /c<-->C2/c phase transition is observed at T (sub c) =286 (10) K. The evolution of the spontaneous strain related to the phase transition with temperature has been studied in detail and compared to available data for pyroxenes with related compositions. Particular attention has been devoted to the ubiquitous presence of residual spontaneous strain after the phase transition by following the structure evolution in order to determine the related microscopic mechanism. The observed mean thermal expansion for the C2/c phase in the temperature interval 423-1073 K is alpha =24.1(1)X10 (super -6) (K (super -1) ), which is similar to that of spodumene, and it is highly anisotropic. The ratio of axial thermal expansion coefficients is alpha (sub a) :alpha (sub b) :alpha (sub c) =2.8:3.6:1, while in spodumene it is 1:2.9:1.3. This represents a clear difference in the mechanism of thermal expansion between the two structures which only differ in the substitution of Al by Ga at the M(1) site. The particular composition studied has fully extended chains of tetrahedra at T>T (sub c) , although significant thermal expansion along c-axis is still observed in the C2/c phase. Extension along the c-axis is resolved therefore by dilatation of the (SiO (sub 4) ) tetrahedron, consequently increasing the thermal expansion along d (sub (100)) by 44% compared to spodumene.


ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 21
Serial Issue: 3
Title: Spontaneous strain variations through the low-temperature displacive phase transition of LiGaSi (sub 2) O (sub 6) clinopyroxene
Title: HP-HT mineral physics; implications for geosciences
Author(s): Camara, FernandoNestola, FabrizioAngel, Ross J.Ohashi, Haruo
Author(s): Comodi, Paolaprefacer
Author(s): Nestola, Fabrizioprefacer
Author(s): Angel, Ross J.prefacer
Affiliation: CNR, Istituto di Geoscienze e Georisorse, Pavia, Italy
Affiliation: Universita di Perugia, Perugia, Italy
Pages: 599-614
Published: 200906
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
Meeting name: Mineralogical International School; HP-HT mineral physics; implications for geosciences
Meeting location: Bressanone, ITA, Italy
Meeting date: 20080211Feb. 11-15, 2008
References: 40
Accession Number: 2009-066490
Categories: Geophysics of minerals and rocks
Document Type: Serial Conference document
Bibliographic Level: Analytic
Illustration Description: illus. incl. 7 tables
Secondary Affiliation: Universita di Padua, ITA, ItalyVirginia Polytechnic Institute and State University, USA, United StatesUniversita di Padova, ITA, ItalyVirginia Polytechnic Institute and State University, USA, United StatesHASHI Institute for Silicate Science, JPN, Japan
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Schweizerbart'sche Verlagsbuchhandlung. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 200936
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