Domain Structure and Polarization Properties of Lanthanum-Substituted Bismuth Titanate Single Crystals

Abstract

Effects of lanthanum substitution on the polarization properties and domain structure of bismuth titanate (BiT, Bi₄Ti₃O₁₂) were investigated using single crystals grown by self-flux method. With increasing La content (BLT, Bi_4-xLa_xTi₃O₁₂), parameter a and unit-cell volume decreased, while parameter b and c increased. The structural analysis revealed that La substitution resulted in a marked decrease in orthorhombic distortion (a/b) from 1.008 (BiT) to 1.000 (x=1.5). The lanthanum substitution resulted in a marked decrease in remanent polarization (P_r) and coercive field (E_c) of BLT single crystals along a-axis. The domain structures in the a-b plane were investigated with polarization microscopy and piezoelectric force microscopy (PFM). BiT had a striped 90-deg domain structure as well as a complex 180-deg one, and the average domain width was about 8.5μm. La substitution led to a decrease in domain size, and BLT(x=1.20) showed a domain structure with about 2.5μm domain width.