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arXiv · 2409.17022

Improper flexoelectricity in hexagonal rare-earth ferrites

Xin Li·Guodong Ren·Yu Yun·Arashdeep Singh Thind·Amit Kumar Shah·Abbey Bowers·Rohan Mishra·Xiaoshan Xu
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Abstract

Flexoelectricity is a universal effect that generates electric polarization due to broken inversion symmetry caused by local strain gradient. The large strain gradient at nanoscale makes flexo-electric effects, especially in nanoscopic ferroelectric materials, promising in sensors, actuator, energy harvesting, and memory applications. In this work, we studied flexoelectricity in hexagonal ferrites h-YbFeO3, an improper ferroelectric expected to have weak piezoelectricity and low sensitivity to depolarization field, which are advantageous for studying flexoelectric effects. We show that in h-YbFeO3 epitaxial thin films, strain gradient on the order of 10^6 m-1 occurs near grain boundaries and edge dislocation, which has a significant impact on the non-polar K3 structural distortion that induces spontaneous polarization. The phenomenological model based on the Landau theory of improper ferroelectricity suggests an indirect flexoelectric effect on the order of 10 nC/m in h-YbFeO3, which is substantially larger than the expectation from Kogan mechanism. These results reveal a novel microscopic mechanism of coupling between strain gradient and polarization mediated by structural distortion, which we call improper flexoelectricity.

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Xin Li, Guodong Ren, Yu Yun, Arashdeep Singh Thind, Amit Kumar Shah, Abbey Bowers, Rohan Mishra, Xiaoshan Xu. 2024-09-25. Improper flexoelectricity in hexagonal rare-earth ferrites. https://arxiv.org/abs/2409.17022

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