Structural phase transitions in the ferroelectric oxide SrBi2Ta2O9

The structure of SrBi2Ta2O9 between room temperature and 1100degreesC has been studied using high resolution powder neutron diffraction methods. At room temperature the structure is orthorhombic (space group A2(1) am ) and this undergoes an apparently continuous transition to a paraelectric orthorhombic phase in space group Amam near 300degreesC in addition to a transition above 500degreesC to a tetragonal structure in space group I 4/ mmm . This sequence of transitions is consistent with a group theoretical analysis. The low temperature ferroelectric phase is characterised by both rotations of the TaO6 and displacement of the Ta atoms from the center of these octahedra, the paralectric phase contains a single tilt of the TaO6 octahedra while there are no rotations of the TaO6 octahedra in the high temperature tetragonal structure.