Epitaxial strain is a powerful means to engineer emergent phenomena in thin films and heterostructures. Here, we demonstrate that KTaO3, a cubic perovskite in bulk form, can be epitaxially strained into a highly tunable ferroelectric. KTaO3 films grown commensurate to SrTiO3 (001) substrates experience an in-plane strain of -2.1 % that transforms the cubic structure into a tetragonal polar phase with transition temperature of 475 K, consistent with our thermodynamic calculations. We show that the Curie temperature and the spontaneous electric polarization can be system- atically controlled with epitaxial strain. Scanning transmission electron microscopy reveals cooperative polar displacements of the potassium columns with respect to the neighboring tantalum columns at room temperature. Optical second-harmonic generation results are described by a tetragonal polar point group (4mm), indicating the emergence of a global polar ground state. We observe a ferroelectric hysteresis response, using metal-insulator-metal capacitor test structures. The results demon- strate a robust intrinsic ferroelectric state in epitaxially strained KTaO3 thin films.
@article{arxiv.2601.14627,
title = {Above Room Temperature Ferroelectricity in Epitaxially Strained KTaO3},
author = {Tobias Schwaigert and Salva Salmani-Rezaie and Sankalpa Hazra and Utkarsh Saha and Maya Ramesh and Aiden Ross and Betul Pamuk and Long-Qing Chen and David A. Muller and Darrell G. Schlom and Venkatraman Gopalan and Kaveh Ahadi},
journal= {arXiv preprint arXiv:2601.14627},
year = {2026}
}