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arXiv · 2601.14627

Above Room Temperature Ferroelectricity in Epitaxially Strained KTaO3

Tobias Schwaigert·Salva Salmani-Rezaie·Sankalpa Hazra·Utkarsh Saha·Maya Ramesh·Aiden Ross·Betul Pamuk·Long-Qing Chen·David A. Muller·Darrell G. Schlom·Venkatraman Gopalan·Kaveh Ahadi
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Abstract

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.

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Tobias Schwaigert, Salva Salmani-Rezaie, Sankalpa Hazra, Utkarsh Saha, Maya Ramesh, Aiden Ross, Betul Pamuk, Long-Qing Chen, David A. Muller, Darrell G. Schlom, Venkatraman Gopalan, Kaveh Ahadi. 2026-01-21. Above Room Temperature Ferroelectricity in Epitaxially Strained KTaO3. https://doi.org/10.1002/adma.74366

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