Interfacial Strain-Insensitive\nThermal and Electrical\nStability of (K,Na)NbO<sub>3</sub>‑Based Lead-Free Ferroelectric\nFilms

Despite\nthe inherent strain relaxation in perovskite-type\noxide\nferroelectric films that occurs beyond a certain thickness, the interfacial\nstates, including carrier and strain, can still influence their electrical\nproperties. This study explores the impact of different (La<sub>0.67</sub>,Sr<sub>0.33</sub>)MnO<sub>3</sub> (LSMO)-coated perovskite-type\noxide substrates on the electrical performance of (K,Na)NbO<sub>3</sub> (KNN)-based ferroelectric films. Specifically, 200 nm-thick epitaxial\nKNN-based films were grown on four distinct substrates: (001)-oriented\nKTaO<sub>3</sub>, SrTiO<sub>3</sub>, LaAlO<sub>3</sub>, and YAlO<sub>3</sub>. Notably, the lattice constants of the KNN-based films remained\nunchanged, despite the varying lattice constants of their substrates.\nThe electrical properties of these films were found to be insensitive\nto the underlying substrate. All films displayed comparable hysteresis\nloops and frequency-dependent dielectric curves, with a consistent\nremnant polarization of ∼63 μC/cm<sup>2</sup> and a dielectric\nconstant of ∼1250 at 1 kHz. Furthermore, the KNN-based films\ndemonstrated exceptional thermal stability. They showed resilience\nunder multiple switching cycles and maintained stable ferroelectricity\nup to a high temperature of 100 °C. These observations underscore\nthe high electrical and thermal stability of KNN-based ferroelectric\nfilms, suggesting their promising potential for applications in electronic\ndevices. This research highlights the robustness and versatility of\nKNN-based ferroelectric films, which could pave the way for their\nintegration into advanced electronic technologies.