Abstract
Enhanced susceptibilities in ferroelectrics often arise near phase boundaries between competing ground states. While chemically-induced phase boundaries have enabled ultrahigh electrical and electromechanical responses in lead-based ferroelectrics, precise chemical tuning in lead-free alternatives, such as (K,Na)NbO3 thin films, remains challenging due to the high volatility of alkali metals. Here, we demonstrate strain-induced morphotropic phase boundary-like polymorphic nanodomain structures in chemically simple, lead-free, epitaxial NaNbO3 thin films. Combining ab initio simulations, thin-film epitaxy, scanning probe microscopy, synchrotron X-ray diffraction, and electron ptychography, we reveal a labyrinthine structure comprising coexisting monoclinic and bridging triclinic phases near a strain-induced phase boundary. The coexistence of energetically competing phases facilitates field-driven polarization rotation and phase transitions, giving rise to a multi-state polarization switching pathway and large enhancements in dielectric susceptibility and tunability across a broad frequency range. Our results open new possibilities for engineering lead-free thin films with enhanced functionalities for next-generation applications.
| Original language | English |
|---|---|
| Article number | 7766 |
| Journal | Nature Communications |
| Volume | 16 |
| Issue number | 1 |
| DOIs | |
| State | Published - Dec 2025 |
Funding
R.G. and R.X. acknowledge the support from the National Science Foundation (NSF) under award No. DMR-2442399 and the American Chemical Society Petroleum Research Fund under award No. 68244-DNI10. K.P., S.P., and L.B. thank an ARA Impact Grant 3.0, the Vannevar Bush Faculty Fellowship (VBFF) Grant No. N00014-20-1-2834 from the Department of Defense. K.P., S.P., L.B., H.K., and D.A.M. acknowledge funding from the ETHOS MURI grant W911NF-21-2-0162 from the Army Research Office (ARO). A.K., K.J.C., and H.Y.H. acknowledge support by the U.S. DOE, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Contract No. DE-AC02-76SF00515. S.H. and V.G. acknowledge support from the DOE-BES under grant number DE-SC0012375 for optical second harmonic generation measurements. D.S. acknowledges support from the NSF under award number DMR-2143642 for sample fabrication. L.W., C.J.G.M., and J.E.S. acknowledge support from the U.S. Army Research Laboratory under Cooperative Agreement No. W911NF-24-2-0100, and J.E.S. acknowledges support also from the U.S. Army Research Office under grant W911NF-21-1-0126. M.C. acknowledges support from the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under contract FWP-ERKCS89. Y.K. is supported by BES-ECA ERKCZ55. The computational work was conducted fully or in part with the support of the Arkansas High Performance Computing Center which is funded through multiple National Science Foundation grants and the Arkansas Economic Development Commission. Part of the microscopy work was performed at the Center for Nanophase Materials Sciences (CNMS), a DOE Office of Science User Facility at ORNL. This work was supported by the NSF, as part of the Center for Dielectrics and Piezoelectrics under grant nos. IIP-1841453 and IIP-1841466. Work performed at the Center for Nanoscale Materials and Advanced Photon Source, both U.S. Department of Energy Office of Science User Facilities, was supported by the U.S. DOE, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. The electron microscopy studies made use of the Cornell Center for Materials Research shared instrumentation facility instruments supported by the NSF (DMR-2039380). Part of this work was performed at the Stanford Nano Shared Facilities (SNSF) RRID:SCR_023230, supported by the National Science Foundation under award ECCS-2026822. This work was performed in part at the Analytical Instrumentation Facility (AIF) at North Carolina State University, which is supported by the State of North Carolina and the National Science Foundation (award number ECCS-2025064). The AIF is a member of the North Carolina Research Triangle Nanotechnology Network (RTNN), a site in the National Nanotechnology Coordinated Infrastructure (NNCI).