Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.
Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, 53706, WI, USA.
Nat Commun. 2018 Jan 8;9(1):92. doi: 10.1038/s41467-017-02568-z.
Oxygen defect control has long been considered an important route to functionalizing complex oxide films. However, the nature of oxygen defects in thin films is often not investigated beyond basic redox chemistry. One of the model examples for oxygen-defect studies is the layered Ruddlesden-Popper phase LaSr CuO (LSCO), in which the superconducting transition temperature is highly sensitive to epitaxial strain. However, previous observations of strain-superconductivity coupling in LSCO thin films were mainly understood in terms of elastic contributions to mechanical buckling, with minimal consideration of kinetic or thermodynamic factors. Here, we report that the oxygen nonstoichiometry commonly reported for strained cuprates is mediated by the strain-modified surface exchange kinetics, rather than reduced thermodynamic oxygen formation energies. Remarkably, tensile-strained LSCO shows nearly an order of magnitude faster oxygen exchange rate than a compressively strained film, providing a strategy for developing high-performance energy materials.
氧缺陷控制一直被认为是功能化复杂氧化物薄膜的重要途径。然而，在薄膜中，氧缺陷的性质通常不仅仅局限于基本的氧化还原化学。氧缺陷研究的一个典型例子是层状钙钛矿结构的拉顿-珀珀相 LaSrCuO（LSCO），其超导转变温度对外延应变非常敏感。然而，之前对 LSCO 薄膜中应变超导耦合的观察主要是基于对机械翘曲的弹性贡献的理解，很少考虑动力学或热力学因素。在这里，我们报告说，通常报道的应变铜酸盐中的氧非化学计量比是由应变修饰的表面交换动力学介导的，而不是降低的热力学氧形成能。值得注意的是，拉伸应变的 LSCO 的氧交换速率比压缩应变的薄膜快近一个数量级，这为开发高性能能源材料提供了一种策略。
