We studied the effects of La modification on the crystal structure and the ferroelectric polarization properties of SrBi2Ta2O9 (SBT). The 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 a larger remanent polarization. The tilt angle of the 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 SBT, as well as La-modified SBT, indicated that the TaO6 octahedral tilt along the a axis is closely related to coercive field for the SBT system.
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Noguchi et al. (2004) studied this question.
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