Defect Engineering for Control of Polarization Properties in SrBi2Ta2O9

Defect engineering to design for remanent polarization (Pr) and coercive field (Ec) in SrBi2Ta2O9 (SBT) is proposed. Cation vacancies coupled with substituents or oxide vacancies are shown to play an essential role in determining the polarization properties. High-resolution neutron powder diffraction studies revealed that trivalent-cation (Bi, La, and Nd) substitution induces Sr vacancies for the requirement of charge neutrality. Polarization measurements of dense ceramics indicated that Bi substitution led to an increase in 2Pr and the 2Pr value for Sr0.73Bi2.18Ta2O9 was twice as large as that of SBT. Structural refinements revealed that Bi substitution enhances spontaneous polarization (Ps) and the improvement of Ps is responsible for the larger 2Pr observed. La substitution with Sr vacancies increased Pr slightly, but the 2Ec value (41 kV/cm) of La0.33Sr0.5Bi2Ta2O9 was much smaller than that for SBT (57 kV/cm). Nd-substituted SBT showed almost the same Pr of La–SBT, while a high 2Ec (125 kV/cm) was attained for Nd0.33Sr0.5Bi2Ta2O9. It is suggested that the higher Ec found in Nd–SBT is attributed to oxide vacancies produced by the substitution of a very small amount of Nd at the Ta site. Defect engineering is expected to open the way for the design of the polarization properties in SBT.