Epitaxial Strain Control of Ferroelectricity in K(Ta1-xNbx)O3

NON-TECHNICAL DESCRIPTION Modern computing and electronics consume rapidly growing amounts of energy, creating an urgent need for devices that store and process information more efficiently. Ferroelectric materials are promising because they hold an internal electric polarization. This is a built-in separation of positive and negative charge, that can be flipped between states by an electric field. This flip consumes much less energy than moving charge. This behavior makes them useful for computer memory, sensors, and low-power electronics, but meeting future needs requires new ferroelectric materials that can be controlled with precision. This project investigates potassium tantalate niobate (KTN), an oxide system where ferroelectricity and electric polarization can be precisely engineered. By leveraging chemical composition, this material unlocks an exceptional degree of tunability. This allows its electrical properties to be tailored through external stimuli like strain. The project grows this material as a very thin film and uses strain, a slight stretching or squeezing of the film, to control how the atoms sit and how the material responds electrically. By imaging the atomic structure with advanced electron microscopy and measuring the electrical behavior, the project is learning the rules that connect atomic arrangement to ferroelectric performance, replacing trial-and-error discovery with predictive design. This work serves the national interest by addressing the rising energy demand of computing and by strengthening United States capacity in semiconductors and quantum technologies. It trains graduate and undergraduate researchers and supports a K-12 education module, Symmetry Switchers, developed in partnership with the Ohio Supercomputer Center STEM Institute to introduce students to how atomic structure shapes material properties. TECHNICAL DESCRIPTION This research project investigates how epitaxial strain and composition control ferroelectricity in potassium tantalate niobate thin films. This material provides a model system for studying the transition from incipient ferroelectric behavior in potassium tantalate to robust ferroelectricity in potassium niobate, while the nearly identical sizes of tantalum and niobium ions help preserve the crystal framework across the composition range. The project uses molecular beam epitaxy to grow phase-pure, coherently strained thin films with controlled niobium to tantalum ratio on substrates that impose a range of epitaxial strains. It combines global structural measurements with atomic-resolution electron microscopy, including electron ptychography, to quantify cation off-centering, oxygen octahedral distortions, local symmetry breaking, and polar nano-region behavior. These structural measurements are correlated with dielectric, piezoresponse, and capacitor-based electrical measurements to determine how atomic-scale distortions produce macroscopic polarization switching and ferroelectric phase stability. The intellectual merit of the project lies in establishing quantitative synthesis-structure-property relationships and testing the relative roles of displacive and order-disorder mechanisms in this strain-tunable oxide system. The resulting design principles can guide the development of ferroelectric thin films whose properties can be controlled more predictably for future memory, sensing, and low-power logic technologies. The project also advances the national interest by supporting sustainable computing, strengthening United States capacity in semiconductors and quantum materials, and training graduate and undergraduate researchers in thin film synthesis, advanced microscopy, electrical characterization, and data analysis. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.