Strain engineering is an important method to control the structure and properties of functional thin films. Here, a new method to induce chemical strain through controllable substrate strain is proposed, which was first applied to double-perovskite thin films. We significantly improved the ferroelectricity of BiSmFe2O6-δ double-perovskite thin films to ∼4.80 μC/cm2, approximately improved six times. The value is more excellent than that of the orthorhombic double-perovskite ferroelectric systems. Synchrotron-based x-ray diffraction and spherical aberration-corrected scanning transmission electron microscopy show that tensile strain can change the epitaxial growth mode and increase the lattice volume. Meanwhile, first-principles density functional theory calculations show that the tensile strain reduces the formation energy of oxygen vacancy. The increased oxygen vacancies can induce a large negative chemical pressure of −7.69 GPa imposed on the thin films on SrTiO3 substrates. The existence of more oxygen vacancies in the Fe-O octahedra of the thin films drives Fe ions away from their high-symmetrical central position, leading to the improvement of ferroelectricity. In addition, the large polarization and oxygen vacancy migration promote the improved functional properties of the thin films, such as large resistive switching (103 times). This strategy and approach will effectively promote the further application of the novel orthorhombic rare-earth double-perovskite devices.

中文翻译：

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应变控制氧空位用于坚固的铁电 BiSmFe2O6-δ 双钙钛矿外延薄膜

应变工程是控制功能薄膜结构和性能的重要方法。在此，提出了一种通过可控基底应变诱导化学应变的新方法，该方法首次应用于双钙钛矿薄膜。我们将 BiSmFe2O6-δ 双钙钛矿薄膜的铁电性显着提高至 ∼4.80 μC/cm2，大约提高了六倍。该值比正交双钙钛矿铁电体系更加优异。基于同步加速器的X射线衍射和球差校正扫描透射电子显微镜表明，拉伸应变可以改变外延生长模式并增加晶格体积。同时，第一性原理密度泛函理论计算表明，拉伸应变降低了氧空位的形成能。氧空位的增加会导致对 SrTiO3 衬底上的薄膜施加 -7.69 GPa 的大负化学压力。薄膜Fe-O八面体中更多氧空位的存在驱使Fe离子远离其高对称中心位置，从而提高铁电性。此外，大的极化和氧空位迁移促进了薄膜功能性能的提高，例如大电阻切换（103倍）。该策略和方法将有效促进新型正交稀土双钙钛矿器件的进一步应用。