Ferroelastic Twin-Wall-Mediated Ferroelectriclike Behavior and Bulk Photovoltaic Effect in ${\mathrm{SrTiO}}_{3}$

Ferroelastic Twin-Wall-Mediated Ferroelectriclike Behavior and Bulk Photovoltaic Effect in ${SrTiO}_{3}$

Ri He, Haowei Xu, Peijun Yang, Kai Chang, Hua Wang, and Zhicheng Zhong

Phys. Rev. Lett. 132, 176801 – Published 26 April 2024

Abstract

Ferroelastic twin walls in nonpolar materials can give rise to a spontaneous polarization due to symmetry breaking. Nevertheless, the bistable polarity of twin walls and its reversal have not yet been demonstrated. Here, we report that the polarity of ${SrTiO}_{3}$ twin walls can be switched by an ultralow strain gradient. Using first-principles-based machine-learning potential, we demonstrate that the twin walls can be deterministically rotated and realigned in specific directions under the strain gradient, which breaks the inversion symmetry of a sequence of walls and leads to a macroscopic polarization. The system can maintain polarity even after the constraint is removed. As a result, the polarization of twin walls can exhibit a ferroelectriclike hysteresis loop upon cyclic bending, namely flexoferroelectricity. Finally, we propose a scheme to experimentally detect the polarity of the twin wall by measuring the bulk photovoltaic responses. Our findings suggest a twin-wall-mediated flexoferroelectricity in ${SrTiO}_{3}$ , which could be potentially exploited as functional elements in nanoelectronic devices design.

Received 16 October 2023
Revised 8 February 2024
Accepted 29 March 2024

DOI:https://doi.org/10.1103/PhysRevLett.132.176801

Physics Subject Headings (PhySH)

Electrical properties Flexoelectricity

Ferroelectrics Flexoelectrics

Density functional theory Machine learning

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Ri He ^1,*, Haowei Xu^2,*, Peijun Yang ¹, Kai Chang^3,5, Hua Wang^3,4,5,†, and Zhicheng Zhong ^1,6,‡

¹Key Laboratory of Magnetic Materials Devices & Zhejiang Province Key Laboratory of Magnetic Materials and Application Technology, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, China
²Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
³Center for Quantum Matter, Zhejiang University, Hangzhou 310058, China
⁴ZJU-Hangzhou Global Scientific and Technological Innovation Center, Hangzhou 311215, China
⁵School of Physics, Zhejiang University, Hangzhou 310058, China
⁶Suzhou Institute for Advanced Research, University of Science and Technology of China, Suzhou 215123, China

^*These authors contributed equally to this work.
^†Corresponding author: daodaohw@zju.edu.cn
^‡Corresponding author: zhong@nimte.ac.cn

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Vol. 132, Iss. 17 — 26 April 2024

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Figure 1
Twin-wall structure and polarization profile in tetragonal phase ${SrTiO}_{3}$ . (a) Schematics of atomistic structure of the twin wall (the tilting octahedral distortions are exaggerated). Blue arrows in the twin wall indicate the direction of the spontaneous polarization, which is parallel to the TWs. Profile of (b) vector $φ$ and (c) polarization across the four antisymmetric twin walls in four-state domains supercell.
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Figure 2
(a) Schematic representation of the domain and twin-wall structure in a film with $a - c$ domains. The $+$ and $-$ signs indicate the simplified point charge lattice model corresponding to the region marked with red dashed square in (b). (b) The surface is tilted at the intersection between $a$ (blue) and $c$ (red) domains with an angle of $\tan (α) = (c / a)$ . The red lines represent the orientation of elongate axes. (c) If the orientation of the wall rotates by 90˚ with respect to the elongate axes of adjacent tetragonal domains, then the polarization can be switched. This indicates that the polarity in the TW possesses bistable states, which can be switched by the wall’s orientation.
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Figure 3
The twin-wall patterns of the ${SrTiO}_{3}$ membrane upon uniaxial compression and bending at 10 K. (a) The DP optimized 132604-atom supercell ( $4 0.0 nm \times 1 2.1 nm \times 3 nm$ ) containing two antisymmetrical TWs. The insets show the local enlarged atomic structure of two TWs. (b)–(d) The axial vector of staggered rotations of ${TiO}_{6}$ octahedra ( $φ$ ) configurations at strain-free, uniaxial compression, and bending strain. The blue and red arrows represent the vector $φ$ with components [100] and [001], respectively. (e),(f) Schematic representation of membrane geometry under strain-free and bending deformation conditions.
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Figure 4
(a) The ${SrTiO}_{3}$ membrane with two TWs exhibits polarization vs gradient-stress hysteresis loop. The insets show the polar (states 1 and 2) and nonpolar (state 0) patterns in corresponding regions. (b) The energy landscape in the transition path of TW rotation (transition from state 0 to states 1 and 2).
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Figure 5
Nonlinear optical (NLO) responses on twin wall: (a),(b) Different components of the local BPV conductivity tensor as a function of light frequency $ω$ . The inset of (a) shows the local electric polarization along the $x$ direction. Two regions with opposite polarizations are labeled with $L = ↑$ and $↓$ . (c),(d) show the contributions from each $k$ point in the Brillouin zone to the local BPV conductivity in the $↑$ polarization region. (c),(d) are for $σ_{x x}^{x}$ and $σ_{y y}^{x}$ , respectively. The color bar is in arbitrary unit.
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Physical Review Letters

Ferroelastic Twin-Wall-Mediated Ferroelectriclike Behavior and Bulk Photovoltaic Effect in SrTiO3

Ri He, Haowei Xu, Peijun Yang, Kai Chang, Hua Wang, and Zhicheng Zhong

Phys. Rev. Lett. 132, 176801 – Published 26 April 2024

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Ferroelastic Twin-Wall-Mediated Ferroelectriclike Behavior and Bulk Photovoltaic Effect in ${SrTiO}_{3}$