Ferroelectric properties and structure distortion in A-site-modified SrBi2Ta2O9

The influence of Ca and Ba modification on the ferroelectric properties of SrBi2Ta2O9 (SBT) was investigated using dense ceramics, and their crystal structures were analyzed by the Rietveld method through high-resolution neutron powder diffraction. The 30% substitution of Sr by a larger Ba lowered the Curie temperature (TC) and decreased remanent polarization (2Pr). In contrast, and equal amount of smaller Ca modification resulted in a marked increase in TC and in a much higher coercive field, but did not improve 2Pr at an applied field lower than 200 kV/cm. Structure refinement revealed that spontaneous polarization (Ps) is determined by the average shift of perovskite blocks along the a axis, and that the Ca-modified SBT had almost the same Ps as SBT. The 30% Ca incorporation did not improve the intrinsic polarization, however enhanced TaO6 octahedral rotation in the a-b plane, which would lead to the higher TC. (author)