Abstract
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.