Fan Zhen, Wang John, Sullivan Michael B, Huan Alfred, Singh David J, Ong Khuong P
Department of Materials Science and Engineering, National University of Singapore, 9 Engineering Drive 1, 117576, Singapore.
Institute of High Performance Computing, Agency of Science, Technology and Research (A*STAR), 1 Fusionopolis Way, 138632, Singapore.
Sci Rep. 2014 Apr 10;4:4631. doi: 10.1038/srep04631.
We explore BiFeO3 under tensile strain using first-principles calculations. We find that the actual structures are more complex than what had been previously thought, and that there is a strong shear deformation type structural instability which modifies the properties. Specifically, we find that normal tensile strain leads to structural instabilities with a large induced shear deformation in (001) BiFeO3 thin films. These induced shear deformations in (001) BiFeO3 thin films under tension stabilize the (001) BiFeO3 thin films and lead to Cc and Ima2 phases that are more stable than the Pmc21 phase at high tensile strain. The induced shear deformation shifts the Cc to Ima2 phase transition towards lower tensile strain region (~1% less), prevents monoclinic tilt and oxygen octahedral tilts, and increases the ferroelectric polarization. The induced shear deformation also strongly affects the electronic structure. The results are discussed in relation to growth of BiFeO3 thin films on cubic and tetragonal substrates involving high levels of tensile strain.
我们使用第一性原理计算方法研究了拉伸应变下的BiFeO₃。我们发现实际结构比之前认为的更为复杂，并且存在一种强烈的剪切变形型结构不稳定性，这种不稳定性改变了材料的性能。具体而言，我们发现正常的拉伸应变会导致(001) BiFeO₃薄膜中出现具有大诱导剪切变形的结构不稳定性。在拉伸状态下，(001) BiFeO₃薄膜中的这些诱导剪切变形使(001) BiFeO₃薄膜稳定，并导致在高拉伸应变下Cc相和Ima2相比Pmc21相更稳定。诱导剪切变形将Cc相向Ima2相的转变移向较低的拉伸应变区域（约低1%），防止单斜倾斜和氧八面体倾斜，并增加铁电极化。诱导剪切变形还强烈影响电子结构。我们结合在涉及高拉伸应变的立方和四方衬底上生长BiFeO₃薄膜的情况对结果进行了讨论。
