Ferroelectric Properties and Structure Distortion in A-Site-Modified SrBi 2 Ta 2 O 9

The influence of Ca and Ba modification on the ferroelectric properties of SrBi 2 Ta 2 O 9 (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 ( T C ) and decreased remanent polarization (2 P r ). In contrast, an equal amount of smaller Ca modification resulted in a marked increase in T C and in a much higher coercive field, but did not improve 2 P r at an applied field lower than 200 kV/cm. Structure refinement revealed that spontaneous polarization ( P s ) is determined by the average shift of perovskite blocks along the a axis, and that the Ca-modified SBT had almost the same P s as SBT. The 30% Ca incorporation did not improve the intrinsic polarization, however enhanced TaO 6 octahedral rotation in the a - b plane, which would lead to the higher T C .