The crystal structure of Aurivillius phase ferroelectric Bi2WO6 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 P2(1)ab to B2cb occurs at about 660 degrees C. This transition corresponds to the loss of one octahedral tilt mode within the perovskite-like WO4 layer of the structure. A second, reconstructive, phase transition occurs around 960 degrees C, corresponding to the ferroelectric Curie point; in contrast to previous suggestions, the structure of this high-temperature phase contains layers of stoichiometry WO4, with WO6 octahedra sharing edges and corners, and with the fluorite-like Bi2O2 layers remaining essentially unchanged. This structure is closely related to that of the ambient temperature phase of lanthanide-doped derivatives, for example, Bi0.7Yb1.3WO6 recently reported. This phase-transition behaviour is in stark contrast to that of other members of the Aurivillius family, such as SrBi2Ta2O9 and Bi4Ti3O12, which retain the archetypal Aurivillius connectivity at all temperatures.
Structure D 2000Unusual High-Temperature Structural Behavior in Ferroelectric Bi 2 WO 6 . -The crystal structure of the title compound is characterized by high-resolution powder neutron diffraction as a function of temperature. A transition from space group P21ab to B2cb occurs at about 660°C and a second transition to space group A2/m around 960°C. The structure of this high-temperature phase contains layers of stoichiometry WO 4 , with WO 6 octahedra sharing edges and corners, and the fluorite-like Bi 2 O 2 layers remaining essentially unchanged. This phase-transition behavior is in contrast to that of other members of the Aurivillius family, such as SrBi2Ta2O9 and Bi4Ti3O12, which retain the archetypal Aurivillius connectivity at all temperatures. -(MCDOWELL, N. A.; KNIGHT, K. S.; LIGHTFOOT*, P.; Chem. Eur.
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