Defect and Strain Engineering Coenhanced Nanoscale Ferroelectricity in SrTiO<sub>3</sub> Thin Films
Chao Chen, Caiwen Li, Jiangxiao Li, Han Gao, Jingtian Zhou, Zhen Wang, Xiangbin Cai, Guofeng Liang, Xiaozhe Yin, Zhibang Shen, Jinhui Yu, Zedong Xu, Minghui Qin, Xubing Lu, Lang Chen, Ning Wang, Ye Zhu, Yu Chen, Guofu Zhou, Xingsen Gao, Yibo Han, Zhenlin Luo, Jun‐Ming Liu, Deyang Chen
Abstract
Tensile biaxial strain has been demonstrated to induce in-plane ferroelectricity in SrTiO 3 thin films at room temperature. However, out-of-plane ferroelectricity is more favorable for electronic device applications. Here, we report the achievement of room-temperature out-of-plane ferroelectric SrTiO 3 thin films with giant tetragonality ( c / a ∼ 1.061) and an ultrahigh ferroelectric stablity temperature (>1000 K) through epitaxial strain and defect engineering. Optical second-harmonic generation (SHG) proves that the enhancement of tetragonality enables improved ferroelectricity. Moreover, a combination of scanning transmission electron microscopy (STEM) and X-ray absorption near-edge spectroscopy (XANES) reveals the origin of enhanced tetragonality and strong ferroelectricity in defect- and strain-codriven supertetragonal SrTiO 3 thin films. Our findings present an approach to material design that can be extended to other material systems for the enhancement of ferroelectricity and the observation of emergent phenomena.