A study was made of the effects of La modification on the crystal structure and ferroelectric polarization properties of SrBi2Ta2O9. Rietveld refinement of neutron powder diffraction demonstrated that La3+ substitution, preferentially at the Sr2+ site (perovskite A site), resulted in A-site vacancies for charge compensation. Polarization measurements revealed that La modification led to a much lower coercive field and to a larger remanent polarization. The tilt-angle of TaO6 octahedra from the c-axis remained constant, but La modification decreased the tilt-angle along the polarization direction (the component along the a axis). The results for Ca-, Ba- and Pb-substituted SrBi2Ta2O9, as well as for La-modified SrBi2Ta2O9, indicated that the TaO6 octahedral tilt along the a axis was closely related to the coercive field in the SrBi2Ta2O9 system.

Cation-Vacancy Induced Low Coercive Field in La-Modified SrBi2Ta2O9. Y.Noguchi, M.Miyayama, K.Oikawa, T.Kamiyama: Journal of Applied Physics, 2004, 95[8], 4261-6