Defect Engineering for Control of Polarization Properties in SrBi 2 Ta 2 O 9

Defect engineering to design for remanent polarization ( P r ) and coercive field ( E c ) in SrBi 2 Ta 2 O 9 (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 2 P r and the 2 P r value for Sr 0.73 Bi 2.18 Ta 2 O 9 was twice as large as that of SBT. Structural refinements revealed that Bi substitution enhances spontaneous polarization ( P s ) and the improvement of P s is responsible for the larger 2 P r observed. La substitution with Sr vacancies increased P r slightly, but the 2 E c value (41 kV/cm) of La 0.33 Sr 0.5 Bi 2 Ta 2 O 9 was much smaller than that for SBT (57 kV/cm). Nd-substituted SBT showed almost the same P r of La–SBT, while a high 2 E c (125 kV/cm) was attained for Nd 0.33 Sr 0.5 Bi 2 Ta 2 O 9 . It is suggested that the higher E c 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.