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Tilting of semi-rigid GaF6 octahedra in GaF3 at high pressures

Published online by Cambridge University Press:  12 January 2017

Jens-Erik Jørgensen ,
Yaroslav Filinchuk  and
Vladimir Dmitriev
Jens-Erik Jørgensen*
Affiliation:
Department of Chemistry, Aarhus University, Aarhus C, Denmark
Yaroslav Filinchuk
Affiliation:
Institute of Condensed Matter and Nanosciences, Universiteé Catholique de Louvain, Place L. Pasteur 1, B-1348, Louvain-la-Neuve, Belgium
Vladimir Dmitriev
Affiliation:
Swiss-Norwegian Beam Lines, European Synchrotron Radiation Facilities, BP 220, F-38043 Grenoble Cedex, France
*
a)Author to whom correspondence should be addressed. Electronic mail: jenserik@chem.au.dk
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Abstract

The VF3-type compound GaF3 has been studied by high-pressure angle-dispersive X-ray diffraction in the pressure range from 0.0001 to 10 GPa. The compression mechanism was found to be highly anisotropic. The c-axis shows little pressure dependence (≈0.4%), but exhibits negative linear compressibility up to ≈3 GPa where it achieves its maximum length. In contrast, the length of the a-axis is reduced by ≈8.8% at the highest measured pressure and an anomalous reduction in the linear compressibility is observed at 4 GPa. The zero pressure bulk modulus B0 was determined to B0 = 28(1) GPa. The compression mechanism of GaF3 is discussed in terms of deformation of an 8/3/c2 sphere-packing model. The volume reduction of GaF3 is mainly achieved through coupled rotations of the GaF6 octahedra within the entire measured pressure range, which reduces the volume of the cubooctahedral voids. In addition, the volume of the GaF6 octahedra also decreases for p ≲ 4.0 GPa, but remains constant above this pressure. The volume reduction of the GaF6 octahedra is accompanied by an increasing octahedral strain. Isosurfaces of the procrystal electron density are used for visualization of the cubooctahedral voids at different pressures.

Keywords

high-pressurecompression mechanismvoid space
Type
Technical Articles
Information
Powder Diffraction , Volume 32 , Supplement S1 , September 2017 , pp. S69 - S73
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Copyright
Copyright © International Centre for Diffraction Data 2017 

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