Effects of Ce and Pr modifications on the ferroelectric distortion, defect structure, and polarization properties were investigated for layered ferroelectric SrBi2Ta2O9 (SBT). Neutron powder diffraction and X-ray photoelectron analyses showed that these rare-earth ions were substituted at the Sr site as RE3+ and that Sr vacancies were created for compensating the charge difference between Sr2+ and RE3+. Oxygen vacancies were present in perovskite layers for Pr–SBT, but in both perovskite and Bi2O2 layers for Ce–SBT. Polarization measurements using dense ceramics indicated that Pr modification led to an marked improvement of polarization properties while Ce-modified SBT exhibited a lower remanent polarization caused by domain pinning and polarization-hysteresis shift. The O vacancies in the Bi2O2 layers were suggested to induce the deterioration such as the domain pinning and hysteresis shift in the SBT system.

Polarization Properties and Oxygen-Vacancy Distribution of SrBi2Ta2O9 Ceramics Modified by Ce and Pr. M.Miyayama, Y.Noguchi: Journal of the European Ceramic Society, 2005, 25[12], 2477-82