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Strain-induced lead-free morphotropic phase boundary

Ghanbari, Reza [North Carolina State University, Raleigh, NC (United States)]·KP, Harikrishnan [Cornell University, Ithaca, NY (United States)] (ORCID:0000000277062758)·Patel, Kinnary [University of Arkansas, Fayetteville, AR (United States)] (ORCID:0000000213805858)·Zhou, Hua [Argonne National Laboratory (ANL), Argonne, IL (United States)] (ORCID:0000000196428674)·Zhou, Tao [Argonne National Laboratory (ANL), Argonne, IL (United States)] (ORCID:0000000280937666)·Liu, Rui [Argonne National Laboratory (ANL), Argonne, IL (United States)] (ORCID:0000000250397419)·Wu, Liyan [Drexel University, Philadelphia, PA (United States)]·Khandelwal, Aarushi [Stanford University, CA (United States); SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)] (ORCID:000000015747482X)·Crust, Kevin J. [SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States); Stanford University, CA (United States)]·Hazra, Sankalpa [The Pennsylvania State University, University Park, PA (United States)]·Carroll, John [Drexel University, Philadelphia, PA (United States); DEVCOM C5ISR U.S. Army, Aberdeen Proving Grounds, MD (United States)]·Meyers, Cedric J. G. [Drexel University, Philadelphia, PA (United States)] (ORCID:0009000402632834)·Wang, Jiayue [Stanford University, CA (United States); SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)] (ORCID:0000000220273634)·Prosandeev, Sergey [University of Arkansas, Fayetteville, AR (United States)]·Qiao, Huimin [North Carolina State University, Raleigh, NC (United States)] (ORCID:0000000195567832)·Kim, Young-Hoon [Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)] (ORCID:0000000173431512)·Nabei, Yoji [North Carolina State University, Raleigh, NC (United States)] (ORCID:0000000151077540)·Chi, Miaofang [Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States); Duke University, Durham, NC (United States)]·Sun, Dali [North Carolina State University, Raleigh, NC (United States)] (ORCID:0000000346623265)·Balke, Nina [North Carolina State University, Raleigh, NC (United States)]·Holt, Martin [Argonne National Laboratory (ANL), Argonne, IL (United States)] (ORCID:0000000326407100)·Gopalan, Venkatraman [The Pennsylvania State University, University Park, PA (United States)] (ORCID:0000000168663677)·Spanier, Jonathan E. [Drexel University, Philadelphia, PA (United States)] (ORCID:0000000230962644)·Muller, David A. [Cornell University, Ithaca, NY (United States); Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY (United States)] (ORCID:0000000341290473)·Bellaiche, Laurent [University of Arkansas, Fayetteville, AR (United States); Tel Aviv University (Israel)] (ORCID:0000000261812024)·Hwang, Harold Y. [Stanford University, CA (United States); SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)] (ORCID:0000000292303214)·Xu, Ruijuan [North Carolina State University, Raleigh, NC (United States)] (ORCID:0000000150460599)
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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)NbO 3 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 NaNbO 3 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.

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Ghanbari, Reza [North Carolina State University, Raleigh, NC (United States)], KP, Harikrishnan [Cornell University, Ithaca, NY (United States)] (ORCID:0000000277062758), Patel, Kinnary [University of Arkansas, Fayetteville, AR (United States)] (ORCID:0000000213805858), Zhou, Hua [Argonne National Laboratory (ANL), Argonne, IL (United States)] (ORCID:0000000196428674), Zhou, Tao [Argonne National Laboratory (ANL), Argonne, IL (United States)] (ORCID:0000000280937666), Liu, Rui [Argonne National Laboratory (ANL), Argonne, IL (United States)] (ORCID:0000000250397419), Wu, Liyan [Drexel University, Philadelphia, PA (United States)], Khandelwal, Aarushi [Stanford University, CA (United States); SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)] (ORCID:000000015747482X), Crust, Kevin J. [SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States); Stanford University, CA (United States)], Hazra, Sankalpa [The Pennsylvania State University, University Park, PA (United States)], Carroll, John [Drexel University, Philadelphia, PA (United States); DEVCOM C5ISR U.S. Army, Aberdeen Proving Grounds, MD (United States)], Meyers, Cedric J. G. [Drexel University, Philadelphia, PA (United States)] (ORCID:0009000402632834), Wang, Jiayue [Stanford University, CA (United States); SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)] (ORCID:0000000220273634), Prosandeev, Sergey [University of Arkansas, Fayetteville, AR (United States)], Qiao, Huimin [North Carolina State University, Raleigh, NC (United States)] (ORCID:0000000195567832), Kim, Young-Hoon [Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)] (ORCID:0000000173431512), Nabei, Yoji [North Carolina State University, Raleigh, NC (United States)] (ORCID:0000000151077540), Chi, Miaofang [Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States); Duke University, Durham, NC (United States)], Sun, Dali [North Carolina State University, Raleigh, NC (United States)] (ORCID:0000000346623265), Balke, Nina [North Carolina State University, Raleigh, NC (United States)], Holt, Martin [Argonne National Laboratory (ANL), Argonne, IL (United States)] (ORCID:0000000326407100), Gopalan, Venkatraman [The Pennsylvania State University, University Park, PA (United States)] (ORCID:0000000168663677), Spanier, Jonathan E. [Drexel University, Philadelphia, PA (United States)] (ORCID:0000000230962644), Muller, David A. [Cornell University, Ithaca, NY (United States); Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY (United States)] (ORCID:0000000341290473), Bellaiche, Laurent [University of Arkansas, Fayetteville, AR (United States); Tel Aviv University (Israel)] (ORCID:0000000261812024), Hwang, Harold Y. [Stanford University, CA (United States); SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)] (ORCID:0000000292303214), Xu, Ruijuan [North Carolina State University, Raleigh, NC (United States)] (ORCID:0000000150460599). 2025-08-20. Strain-induced lead-free morphotropic phase boundary. https://doi.org/10.1038/s41467-025-63041-w

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