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

This work investigates the substitution of Ce donor for Bi at A-site, which effectively improves the piezoelectricity and electrical resistivity of Aurivillius-phase CaBi ₄Ti ₄O ₁₅ (CBT) ceramic. Crystal structures of CaBi _{4- x}Ce _xTi ₄O ₁₅ 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 (Bi ₂O ₂) 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 (Bi ₂O ₂) ²⁺ layer and perovskite block is strong enhanced. Meanwhile, fewer defect dipoles ( V ″ ′ Bi − V O • • ) dipoles in Ce-doped CBT ceramics result in a less internal bias field ( E _ib ), 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 ( ρ _dc ) and activation energy of the charge carriers ( E _a) are effectively enhanced in Ce-doped CBT ceramics.