Switchable order parameters in ferroic materials are essential for functional electronic devices, yet disruptions of the ordering can take the form of planar boundaries or defects that exhibit distinct properties from the bulk, such as electrical (polar) or magnetic (spin) response. Characterizing the structure of these boundaries is challenging due to their confined size and three-dimensional nature. Here, a chemical anti-phase boundary in the highly ordered double perovskite Pb₂MgWO₆ is investigated using multislice electron ptychography. The boundary is revealed to be inclined along the electron beam direction with a finite width of chemical intermixing. Additionally, regions at and near the boundary exhibit antiferroelectric-like displacements, contrasting with the predominantly paraelectric matrix. Spatial statistics and density functional theory calculations further indicate that despite their higher energy, chemical anti-phase boundaries form due to kinetic constraints during growth, with extended antiferroelectric-like distortions induced by the chemically frustrated environment in the proximity of the boundary. The three-dimensional imaging provides critical insights into the interplay between local chemistry and the polar environment, elucidating the role of anti-phase boundaries and their associated confined structural distortions and offering new opportunities for engineering ferroic thin films.

Four-dimensional scanning transmission electron microscopy datasets are collected with EMPAD (.raw, .xml). Mutlislice electron ptychography reconstructions (.mat) are performed with the foldslice package (https://github.com/yijiang1/fold_slice)(opens in new window) that is built upon the Matlab code developed by the Science IT and the coherent X-ray scattering (CXS) groups at Paul Scherrer Institut, Switzerland: https://www.psi.ch/en/sls/csaxs/software(opens in new window).