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Structural basis for the anomalous low-temperature thermal expansion behaviour of the gillespite-structured phase Ba (sub 0.5) Sr (sub 0.5) CuSi (sub 4) O (sub 10)

Kevin S. Knight and C. Michael B. Henderson
Structural basis for the anomalous low-temperature thermal expansion behaviour of the gillespite-structured phase Ba (sub 0.5) Sr (sub 0.5) CuSi (sub 4) O (sub 10)
European Journal of Mineralogy (March 2007) 19 (2): 189-200

Abstract

The crystal structure of the gillespite-structured phase Ba (sub 0.5) Sr (sub 0.5) CuSi (sub 4) O (sub 10) has been refined from powder neutron time-of-flight data at eight temperatures between 5K and 300K. No structural phase transitions were observed on cooling to the lowest temperature. The temperature dependence of the crystal structure in the a - b plane has been found to be dominated by low energy lattice modes involving cooperative anti-phase rotations of the square-planar CuO (sub 4) group with the Si (sub 4) O (sub 10) polyhedral unit which results in non-Gruneisen behaviour for the a lattice parameter and negative volume thermal expansion to 100K. Concomitant with these rotations is an associated tilting of SiO (sub 4) tetrahedra about the bridging anions resulting in an increasing aplanarity of the Cu site with temperature. The behaviour of the c-axis with temperature is conventional and appears to be related to the tilting of SiO (sub 4) tetrahedra and an increase in the Ba/Sr bond distances resulting in a decrease of the overbonded bond valence sum at the Ba/Sr site.


ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 19
Serial Issue: 2
Title: Structural basis for the anomalous low-temperature thermal expansion behaviour of the gillespite-structured phase Ba (sub 0.5) Sr (sub 0.5) CuSi (sub 4) O (sub 10)
Affiliation: Rutherford Appleton Laboratory, ISIS Facility, Didcot, United Kingdom
Pages: 189-200
Published: 200703
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 26
Accession Number: 2007-045074
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 6 tables
Secondary Affiliation: Daresbury Laboratory, GBR, United Kingdom
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: 200724
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