The existence of a previously unidentified intermediate phase in the ferroelectric−paraelectric transition in Bi4Ti3O12 is established by using a combination of group theory and synchrotron powder diffraction.
A variable-temperature synchrotron X-ray diffraction study of the phase transitions inthe ferroelectric n = 3 Aurivillius oxide Bi4Ti3O12 is described. At room temperature thestructure of Bi4Ti3O12 is orthorhombic in space group B2eb and this continuously transformsto the high-temperature tetragonal I4/mmm structure via an intermediate orthorhombicphase. The possible space groups of this intermediate orthorhombic phase have beenidentified by using group theory.