Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
Nat Mater. 2012 Oct;11(10):888-94. doi: 10.1038/nmat3393. Epub 2012 Aug 19.
Oxygen vacancy distributions and dynamics directly control the operation of solid-oxide fuel cells and are intrinsically coupled with magnetic, electronic and transport properties of oxides. For understanding the atomistic mechanisms involved during operation of the cell it is highly desirable to know the distribution of vacancies on the unit-cell scale. Here, we develop an approach for direct mapping of oxygen vacancy concentrations based on local lattice parameter measurements by scanning transmission electron microscopy. The concept of chemical expansivity is demonstrated to be applicable on the subunit-cell level: local stoichiometry variations produce local lattice expansion that can be quantified. This approach was successfully applied to lanthanum strontium cobaltite thin films epitaxially grown on substrates of different symmetry, where polarized neutron reflectometry revealed a strong difference in magnetic properties. The different vacancy content found in the two films suggests the change in oxygen chemical potential as a source of distinct magnetic properties, opening pathways for structural tuning of the vacancy concentrations and their gradients.
氧空位分布和动力学直接控制固体氧化物燃料电池的运行，并且与氧化物的磁性、电子和输运性质内在相关。为了了解电池运行过程中的原子机制，非常希望知道在单位晶胞尺度上的空位分布。在这里，我们开发了一种基于扫描透射电子显微镜局部晶格参数测量的氧空位浓度直接映射方法。证明了化学膨胀率的概念适用于亚晶胞水平：局部化学计量变化会产生可以量化的局部晶格膨胀。该方法成功应用于在不同对称性衬底上外延生长的镧锶钴氧化物薄膜，其中偏振中子反射测量揭示了磁性的强烈差异。在这两种薄膜中发现的不同空位含量表明氧化学势的变化是产生不同磁性的原因，为空位浓度及其梯度的结构调谐开辟了途径。
