An Atomic-Scale Chemical Switch for Oxide Ferroelectricity

Interfacial chemistry offers new opportunities for designing ferroelectric materials, yet their coupling with intrinsic polarization remains largely unexplored. Here, we synthesize ferroelectric BiFeO3 nanoparticles with {100} facets covered by a Bi2FeO6-x Aurivillius-like phase, allowing the interfacial Bi2O2 layer to interact with bulk polarization at different relative orientations. Using atomic-resolution scanning transmission electron microscopy, we observed a large polarization enhancement when the interface aligned with the bulk polarization, and a polarization reversal when opposing it. In situ heating and first-principles calculations show that the Bi2O2 layer repels the underlying FeO6 octahedra, which either rotate or rigidly displace to accommodate the chemical stress, depending on local geometry. Moreover, this mechanism can imprint local polarization in Aurivillius phases and nonferroelectric oxides, offering a general route to design polar topologies in oxide heterostructures.