Raman study of Bi site-occupancy effect on orientation and polarization in Bi_(4)Ti_(3)O_(12) thin films

摘要

Our Raman study of 0-6 mol % Bi excess Bi_(4)Ti_(3)O_(12) (BIT) films implies that symmetry breaking effect occurs in 0 mol % Bi excess film, which is restored to BIT symmetry in 2-6 mol % Bi excess films. The "rigid layer" mode at 59.22 cm~(-1) implies a higher stability of Bi in the Bi_(2)O_(2) layer than the perovskite layer and that Bi has high preference to incorporate into the Bi_(2)O_(2) layer. Increasing Bi incorporation in the A site enhances the Jahn-Teller distortion of TiO_(6) octahedra and the c orientation. This implies that doping by an ion without an outer orbital like La can decrease the TiO_(6) distortion, change the orientation, and tilt the polarization vector.