Thermal depoling of high Curie point Aurivillius phase ferroelectric ceramics

The thermal depoling behavior of several different Aurivillius phase ferroelectric ceramics has been studied. This includes two-layer (CaBi2Nb2O9,Ca0.9Ba0.1Bi2Nb2O9,Bi3NbTiO9,Bi3Nb1.2Ti0.8O9), three-layer (Bi4Ti3O12), and four-layer [CaBi4Ti4O15,Ca-0.94(Na,Ce)(0.03)Bi4Ti4O15] compounds. All of them have a high Curie point (T-c >= 675 degrees C). The orthorhombic structured materials show good resistance to thermal depoling up to temperatures close to their Curie points. However, Bi4Ti3O12, which has a monoclinic structure, shows a significant reduction in d(33) well before its Curie point. The monoclinic distortion produces more non-180 degrees ferroelectric domain structures, and it is the thermal instability of these that accounts for their thermal depoling behaviour. Excess Nb doping of Bi3NbTiO9 produces a significant reduction in its resistance to thermal depoling, suggesting that the doping produces a lowering of the crystallographic symmetry. (c) 2005 American Institute of Physics.