Robust Ferroelectric Properties in (K,Na)NbO₃-Based Lead-Free Films via a Self-Assembled Nanocomposite Approach

(K,Na)NbO3-based lead-free ferroelectric materials are highly desired in modern electronic applications and have long been considered as a strong candidate for replacing (Pb,Zr)TiO3, but most of them are deficient in large remnant polarization and decent thermal stability. Here, a unique lead-free 0.95(K0.49Na0.49Li0.02)(Nb0.8Ta0.2)O3–0.05CaZrO3 with 2 wt % MnO2 addition (KNNLT-CZ-M) ferroelectric film with special nanocomposite structures grown on La0.7Sr0.3MnO3-coated SrTiO3(001) substrate is demonstrated. The KNNLT-CZ-M films display excellent ferroelectricity with a large twice remnant polarization of 64.91 μC/cm2, a superior thermal stability of ferroelectricity from −196 to 300 °C, and a high Curie temperature of 400 °C. These robust performances could be attributed to the densely arranged self-assembled nanocolumns (∼10 nm in diameter) in the films, which can vertically strain the matrix and enhance its b/a ratio. The formation of the nanocolumns critically depends on the CaZrO3 component. Our results may help the design of a new type of lead-free ferroelectric films and promote their potential applications in microelectronic devices.