Stress-Induced Cubic-to-Hexagonal Phase Transformation in Perovskite Nanothin Films
Stress-Induced Cubic-to-Hexagonal Phase Transformation in Perovskite Nanothin Films
复制标题
钙钛矿纳米薄膜中应力诱导的立方相到六方相变
DOI：
10.1021/acs.nanolett.7b02570
复制
发表时间：
2017-08-01
期刊：
影响因子：
10.8
通讯作者：
Zhang, Tong-Yi
中科院分区：
文献类型：
--
作者：
Cao, Shi-Gu;Li, Yunsong;Zhang, Tong-Yi
晶体结构和机械变形之间的强耦合可以稳定高对称性相中的低对称性相或在氧化物薄膜中诱导新的相变。氧化物薄膜中的应力诱导结构相变因其对材料功能的重要影响而受到越来越多的关注。在这里，我们实验发现了一种新的应力诱导的立方相到六方相转变，经过特殊的热机械处理(TMT)，在不同应力下的BaTiO_3纳米薄膜在575℃的温度下进行热处理，高分辨电子显微镜和拉曼光谱都表明在较高的张应力下，钙钛矿薄膜中有更高密度的六方相。X射线光电子能谱和电子能量损失谱都没有检测到钛原子价态的任何变化，从而排除了氧空位引起的立方到六方(C-H)相变的机制。第一性原理计算表明，在高温下，c-h相变可以通过晶格剪切来完成，这与实验观察到的结果一致。外加弯曲和残余拉应力在纳米素膜中产生剪应力。高温下的热能有助于剪切应力克服c-h相变过程中的势垒。TMT在钙钛矿型纳米薄膜中的应力诱导相变为材料科学家和工程师提供了一种新的方法来定制铁电材料的纳米/微结构和性能。
The strong coupling between crystal structure and mechanical deformation can stabilize low-symmetry phases from high-symmetry phases or induce novel phase transformation in oxide thin films. Stress-induced structural phase transformation in oxide thin films has drawn more and more attention due to its significant influence on the functionalities of the materials. Here, we discovered experimentally a novel stress-induced cubic-to-hexagonal phase transformation in the perovskite nanothin films of barium titanate (BaTiO3) with a special thermomechanical treatment (TMT), where BaTiO3 nanothin films under various stresses are annealed at temperature of 575 degrees C. Both high-resolution transmission electron microscopy and Raman spectroscopy show a higher density of hexagonal phase in the perovskite thin film under higher tensile stress. Both X-ray photoelectron spectroscopy and electron energy loss spectroscopy does not detect any change in the valence state of Ti atoms, thereby excluding the mechanism of oxygen vacancy induced cubic-to-hexagonal (c-to-h) phase transformation. First-principles calculations show that the c-to-h phase transformation can be completed by lattice shear at elevated temperature, which is consistent with the experimental observation. The applied bending plus the residual tensile stress produces shear stress in the nanothin film. The thermal energy at the elevated temperature assists the shear stress to overcome the energy barriers during the c-to-h phase transformation. The stress-induced phase transformation in perovskite nanothin films with TMT provides materials scientists and engineers a novel approach to tailor nano/microstructures and properties of ferroelectric materials.