Origin of high piezoelectricity in CBT-based Aurivillius ferroelectrics: Glide of (Bi2O2)2+ blocks and suppressed internal bias field

Abstract

This work investigates the substitution of Ce donor for Bi at A-site, which effectively improves the piezoelectricity and electrical resistivity of Aurivillius-phase CaBi4Ti4O15 (CBT) ceramic. Crystal structures of CaBi4-xCexTi4O15 ceramics are studied systematically, revealing the reason of unit cell contraction and the decreased ferro-distortion in crystal structure. The first-principles calculation shows that the enhancement of the intrinsic piezoelectricity in Ce-doped CBT ceramics come from the polarization stretching, where the translation and off-center displacement response under macroscopic strain of (Bi2O2)2+ layers playing an unexpectedly significant role. Ce doping can break the long-range ferroelectric chain, softening the flexibility of polarization and then making higher displacement response to strain for the other atoms, specially, the glide between the (Bi2O2)2+ layer and perovskite block is strong enhanced. Meanwhile, fewer defect dipoles (V″′Bi−VO••)dipolesin Ce-doped CBT ceramics result in a less internal bias field (Eib), which favors the polarization rotation and extension. Moreover, the significant role of oxygen vacancy ionization in electrical conductivity is inhibited, so both direct current resistance (ρdc) and activation energy of the charge carriers (Ea) are effectively enhanced in Ce-doped CBT ceramics.