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(K_0.49Na_0.49Li_0.02)(Nb_0.8Ta_0.2)O₃-0.05CaZrO₃ with 2 wt % MnO₂ addition (KNNLT-CZ-M) ferroelectric film with special nanocomposite structures grown on La_0.7Sr_0.3MnO₃-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.