Defect engineering was used to modify the remanent polarization, P, and coercive field, E, of SrBi2Ta2O9. Cation vacancies coupled with substituents or oxide vacancies were shown to play an essential role in determining the polarization properties. High-resolution neutron powder diffraction studies revealed that trivalent-cation (Bi, La, Nd) substitution induced the Sr vacancies required for charge neutrality. Polarization measurements of dense ceramics indicated that Bi substitution led to an increase in 2P. The 2P value of Sr0.73Bi2.18Ta2O9 was twice as large as that of SBT. Structural refinements revealed that Bi substitution enhanced the spontaneous polarization, S, and this improvement was responsible for the larger 2P value observed. The substitution of La by Sr vacancies increased P slightly, but the 2E value (41kV/cm) of La0.33Sr0.5Bi2Ta2O9 was much smaller than that of SBT (57kV/cm). It was found that Nd-substituted SBT exhibited almost the same P of La-SBT, while a high 2E value (125kV/cm) was found in Nd0.33Sr0.5Bi2Ta2O9. It was suggested that the higher E-value found in Nd-SBT was due to oxide vacancies produced by the substitution of a very small amount of Nd at Ta sites.

Defect Engineering for Control of Polarization Properties in SrBi2Ta2O9. Y.Noguchi, M.Miyayama, K.Oikawa, T.Kamiyama, M.Osada, M.Kakihana: Japanese Journal of Applied Physics - 1, 2002, 41[11B], 7062-75