Theory and application of the vector pair correlation function for real-space crystallographic analysis of order/disorder correlations from STEM images
Theory and application of the vector pair correlation function for real-space crystallographic analysis of order/disorder correlations from STEM images
复制标题
DOI：
10.1063/5.0058928
复制
发表时间：
2021-09
期刊：
影响因子：
6.1
通讯作者：
Stephen D. Funni;Z. Yang;M. Cabral;C. Ophus;X. M. Chen;E. Dickey
中科院分区：
文献类型：
--
作者：
Stephen D. Funni;Z. Yang;M. Cabral;C. Ophus;X. M. Chen;E. Dickey
局部结构和化学与平均晶体晶胞的偏差越来越被认为对许多技术上重要的材料的性能有重大影响。在这里，我们提出了矢量对相关函数（vPCF）作为一种新的实空间晶体学分析方法，它可以应用于原子分辨率扫描透射电子显微镜（STEM）图像量化和分析结构有序/无序相关性。我们的基于STEM的vPCF与来自X射线总散射的径向PCF和/或3D对分布函数相比具有几个优势：vPCF明确保留了晶体取向信息，空间分辨，可以直接应用于亚晶格基础，并且适用于可以用STEM成像的任何材料。为了显示我们的方法的实用性，我们测量部分vPCF在Ba 5SmSn 3 Nb 7 O30（BSSN），一个四钨青铜（TTB）结构的复合氧化物。许多TTB被认为是经典或弛豫铁电体，并且这些性质与超晶格有序的存在相关。BSSN，具体地说，表现出弛豫行为和不相称的结构调制。从vPCF的数据，我们观察到，阳离子网站，只有Ba（A2）亚晶格结构调制。然后，我们推断的本地调制矢量，并揭示了显着的各向异性在其相关长度。最后，短程相关的极性位移的B2阳离子网站上观察。这项工作介绍了vPCF作为一个强大的实空间晶体学技术，它可以直接，强大的量化的短程到长程顺序的亚晶格特定的基础上，适用于广泛的复杂材料类型。
Deviations of local structure and chemistry from the average crystalline unit cell are increasingly recognized to have a significant influence on the properties of many technologically important materials. Here, we present the vector pair correlation function (vPCF) as a new real-space crystallographic analysis method, which can be applied to atomic-resolution scanning transmission electron microscopy (STEM) images to quantify and analyze structural order/disorder correlations. Our STEM-based vPCFs have several advantages over radial PCFs and/or 3D pair distribution functions from x-ray total scattering: vPCFs explicitly retain crystallographic orientation information, are spatially resolved, can be applied directly on a sublattice basis, and are suitable for any material that can be imaged with STEM. To show the utility of our approach, we measure partial vPCFs in Ba5SmSn3Nb7O30 (BSSN), a tetragonal tungsten bronze (TTB) structured complex oxide. Many TTBs are known to be classical or relaxor ferroelectrics, and these properties have been correlated with the presence of superlattice ordering. BSSN, specifically, exhibits relaxor behavior and an incommensurate structural modulation. From the vPCF data, we observe that, of the cation sites, only the Ba (A2) sublattice is structurally modulated. We then infer the local modulation vector and reveal a marked anisotropy in its correlation length. Finally, short-range correlated polar displacements on the B2 cation sites are observed. This work introduces the vPCF as a powerful real-space crystallography technique, which enables direct, robust quantification of short-to-long range order on a sublattice-specific basis and is applicable to a wide range of complex material types.