Effect of Bi substitution at the Sr site on the ferroelectric properties of dense strontium bismuth tantalate ceramics

Ferroelectric properties for dense bulk ceramics of Sr-deficient and Bi-excess strontium bismuth tantalate, Sr1-xBi2+xTa2O9, were investigated, and their crystal structures were analyzed by the powder x-ray diffraction Rietveld method. A successful pattern fitting was obtained under the assumption that Bi was substituted at the Sr site for samples with x less than or equal to 0.16, and the lattice in the a-b plane was reduced linearly with an increase in x. Furthermore, dielectric measurements showed that the Curie temperature, T-C, rose with x and the sample with x=0.27 had a T-C of 430 degrees C, which is much higher than that of the stoichiometric sample (x=0: T-C=300 degrees C). These results strongly support the Bi substitution at the Sr site. The polarization hysteresis measurements revealed that a small amount of Bi substitution of 5% results in a marked increase in remanent polarization, however that further Bi substitution is not effective for improving the ferroelectric properties. (C) 2000 American Institute of Physics. [S0021-8979(00)00416-3].