Polarization Pinning at an Antiphase Boundary in Multiferroic YbFeO_3

The switching characteristics of ferroelectrics and multiferroics are influenced by the interaction of topological defects with domain-walls. We report on the pinning of polarization due to antiphase boundaries in thin films of the multiferroic hexagonal YbFeO_3. We have directly resolved the atomic structure of a sharp antiphase boundary (APB) in YbFeO_3 thin films using a combination of aberration-corrected scanning transmission electron microscopy (STEM) and total energy calculations based on density-functional theory (DFT). We find the presence of a layer of FeO_6 octahedra at the APB that bridge the adjacent domains. STEM imaging shows a reversal in the direction of polarization on moving across the APB, which DFT calculations confirm is structural in nature as the polarization reversal reduces the distortion of the FeO_6 octahedral layer at the APB. Such APBs in hexagonal perovskites are expected to serve as domain-wall pinning sites and hinder ferroelectric switching of the domains.