Structural Origin of Morphotropic Phase Boundary in Advanced Perovskite Ferroelectric Oxides

Ferroelectric oxides PbZr_1-xTi_xO₃ (PZT) with the ABO₃ perovskite structure exhibit exceptional polarization responses near their morphotropic phase boundary (MPB), yet the chemical origin of this behavior remains unclear. Here, we show that, in a prototypical composition, 0.05Pb(Mn_1/3Sb_2/3)O₃-0.95PbZr_0.52Ti_0.48O₃, this origin arises from coupled effects of B-site chemical ordering and multi-ion displacement heterogeneity-related disordering. Pronounced anti-self-clustering of Zr and Ti forms a short-range chemical ordering driven by the mismatch between ionic Zr-O and more covalent Ti-O bonds, generating a soft-hard compatible BO₆ network that reduces local stress, which facilitates polarization rotation and switching. Simultaneously, A-site, B-site, and oxygen ions display significant, directionally distinct off-center displacements, producing continuous local monoclinic polar states (M_A-M_B) with coplanar polarization vectors and nanoscale domains with mobile walls. These results show that PZT's extraordinary response emerges from a unity-of-opposites relationship that balances rigidity and flexibility through compatible bonding and multi-ion displacements, offering guidance for designing high-performance ferroelectrics.