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Structure of russellite (Bi 2 WO 6 ): origin of ferroelectricity and the effect of the stereoactive lone electron pair on the structure
Author(s) -
Okudera Hiroki,
Sakai Yuka,
Yamagata Kentaro,
Takeda Hiroaki
Publication year - 2018
Publication title -
acta crystallographica section b
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.604
H-Index - 33
ISSN - 2052-5206
DOI - 10.1107/s2052520618006133
Subject(s) - lone pair , bismuth , ferroelectricity , orthorhombic crystal system , crystallography , neutron diffraction , materials science , electron , crystal structure , condensed matter physics , chemistry , molecule , dielectric , physics , optoelectronics , organic chemistry , quantum mechanics , metallurgy
The structure of the low‐temperature polar (orthorhombic) phase of russellite (Bi 2 WO 6 ) was examined on artificial specimens with precise single‐crystal X‐ray diffraction experiments. The final atomic arrangement thus obtained was identical to that reported by Knight [ Miner. Mag . (1992), 56 , 399–409] with powder neutron diffraction. The residual density attributable to a stereochemically‐active lone pair of electrons of bismuth was prominent at approximately the centre of a larger cap of BiO 8 square antiprisms, that is on the line from the Bi sites to an adjacent WO 4 2− slab along the b ‐axis direction. Quite uneven Bi—O distances and the formation of a vacant coordination hemisphere (within 3 Å) should, therefore, be ascribed to the strong demand of bismuth to form shorter Bi—O bonds to use up its electrostatic charge within its coordination environment. The shift of bismuth along − c propagates via the correlated shift of the W site and these cooperative shifts cause ferroelectricity in the compound. This propagation was easily effected by the intrusion of molecules such as acetone into the structure.