Ferroelectricity in Epitaxial Perovskite Oxide Bi<sub>2</sub>WO<sub>6</sub> Films with One-Unit-Cell Thickness.

Zhou, Song; Liao, Lei; Chen, Lan; Feng, Baojie; He, Xiaoyue; Bai, Xuedong; Song, Chuangye; Wu, Kehui · Nano Lett · 2023

basic_science · Level V

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Abstract

Retaining ferroelectricity in ultrathin films or nanostructures is crucial for miniaturizing ferroelectric devices, but it is a challenging task due to intrinsic depolarization and size effects. In this study, we have shown that it is possible to stably maintain in-plane polarization in an extremely thin, one-unit-cell thick epitaxial Bi<sub>2</sub>WO<sub>6</sub> film. The use of a perfectly lattice-matched NdGaO<sub>3</sub> (110) substrate for the Bi<sub>2</sub>WO<sub>6</sub> film minimizes strain and enhances stability. We attribute the residual polarization in this ultrathin film to the crystal stability of the Bi-O octahedral framework against structural distortions. Our findings suggest that ferroelectricity can surpass the critical thickness limit through proper strain engineering, and the Bi<sub>2</sub>WO<sub>6</sub>/NdGaO<sub>3</sub> (110) system presents a potential platform for designing low-energy consumption, nonvolatile ferroelectric memories.