Atomic Origins of Enhanced Ferroelectricity in Nanocolumnar PbTiO₃/PbO Composite Thin Films

Abstract Nanocomposite films hold great promise for multifunctional devices by integrating different functionalities within a single film. The microstructure of the precipitate/secondary phase is an essential element in designing composites’ properties. The interphase strain between the matrix and secondary phase is responsible for strain‐mediated functionalities, such as magnetoelectric coupling and ferroelectricity. However, a quantitative microstructure‐dependent interphase strain characterization has been scarcely studied. Here, it is demonstrated that the PbTiO₃(PTO)/PbO composite system can be prepared in nano‐spherical and nanocolumnar configurations by tuning the misfit strain, confirmed by a three‐dimensional reconstructive microscopy technique. With the atomic resolution quantitative microscopy with a depth resolution of a few nanometers, it is discovered that the strained region in PTO is much larger and more uniform in nanocolumnar compared to nano‐spherical composites, resulting in much enhanced ferroelectric properties. The interphase strain between PbO and PTO in the nanocolumnar structure leads to a giant c/a ratio of 1.20 (bulk value of 1.06), accompanied by a Ti polarization displacement of 0.48 Å and an effective ferroelectric polarization of 241.7 µC cm⁻², three times compared to the bulk value. The quantitative atomic‐scale strain and polarization analysis on the interphase strain provides an important guideline for designing ferroelectric nanocomposites.