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Unusual High‐Temperature Structural Behaviour in Ferroelectric Bi 2 WO 6
Author(s) -
McDowell Neil A.,
Knight Kevin S.,
Lightfoot Philip
Publication year - 2006
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200500904
Subject(s) - aurivillius , ferroelectricity , materials science , curie temperature , crystallography , phase transition , condensed matter physics , neutron diffraction , perovskite (structure) , phase (matter) , crystal structure , octahedron , ferromagnetism , chemistry , physics , optoelectronics , organic chemistry , dielectric
The crystal structure of Aurivillius phase ferroelectric Bi 2 WO 6 has been studied in detail as a function of temperature by using high‐resolution powder neutron diffraction. In agreement with an earlier study, a transition from space group P 2 1 ab to B 2 cb occurs at about 660 °C. This transition corresponds to the loss of one octahedral tilt mode within the perovskite‐like WO 4 layer of the structure. A second, reconstructive, phase transition occurs around 960 °C, corresponding to the ferroelectric Curie point; in contrast to previous suggestions, the structure of this high‐temperature phase contains layers of stoichiometry WO 4 , with WO 6 octahedra sharing edges and corners, and with the fluorite‐like Bi 2 O 2 layers remaining essentially unchanged. This structure is closely related to that of the ambient temperature phase of lanthanide‐doped derivatives, for example, Bi 0.7 Yb 1.3 WO 6 recently reported. This phase‐transition behaviour is in stark contrast to that of other members of the Aurivillius family, such as SrBi 2 Ta 2 O 9 and Bi 4 Ti 3 O 12 , which retain the archetypal Aurivillius connectivity at all temperatures.