Structural Evolution of Lead Lutetium Niobate‐Based Antiferroelectric Materials

ABSTRACT While the dipolar configurations in prototype antiferroelectric like PbZrO 3 are well‐established, the structural complexity of Pb(B′ 1/2 B′′ 1/2 )O 3 perovskites introduces a rich interplay of competing interactions that remain significantly less understood. This lack of atomic‐scale insight into their modulated ordering has been a critical barrier to the rational design of complex AFE systems with tailored functionalities. Moving beyond the classical PbZrO 3 paradigm, this work provides the first atomic‐level elucidation of the AFE mechanism in a representative complex perovskite, Pb(Lu 1/2 Nb 1/2 )O 3 ceramic and PbTiO 3 ‐modified derivatives. Atomic‐resolution HAADF imaging uncovers a pivotal compositional evolution of the local Pb displacement. In the AFE ground state, Pb displacements undergo a progressive three‐dimensional reorientation: rotating from ∼45°/−135° towards ∼30°/−120° within the a p ‐b p plane, while simultaneously acquiring a significant out‐of‐plane component along the c p ‐axis. This concerted shift aligns the local polarization towards a <111> p ‐direction, thereby effectively reducing the energy barrier for electric‐field‐driven polarization rotation into the ferroelectric <111> p state. This atomistic mechanism directly explains the reduced critical fields and enhanced ferroelectricity upon PT subsitution. These findings provide profound insights into the unique phase transition dynamics and antipolar ordering mechanisms in B‐site complex antiferroelectrics, establishing a new framework for optimizing functional performance through the precise modulation of spatial polar configurations.