Local Atomic Structure and Properties of Transition Metal Oxides using Pair Distribution Function Analysis

本文将利用粉末衍射数据的对分布函数（PDF）分析来研究具有有趣电子性质的过渡金属氧化物（TMOs）的局部结构。该技术利用布拉格散射和漫射散射在很宽的动量传递(Q)范围内，并直接产生原子的短程有序。它超越了完美结晶度的近似，并允许在1-20埃的长度尺度上解决局部结构。这种类型的结构分析将应用于各种过渡金属氧化物，如高tc材料，层状锰酸盐和镍酸盐以及巨磁阻锰酸盐。在这些材料中，结构可以响应电子状态，我们将寻找电学性质变化与局部结构效应之间的相关性。这样，局域电子态的性质，如极化合态、双极化合态和电荷相分离态，将被阐明。据报道，伟大的材料科学家F.C.弗兰克曾说过：“晶体就像人一样——正是缺陷使他们变得有趣。”事实上，许多最有趣、最有用的新材料都表现出高度的原子无序性；往往是这些缺陷赋予了它们有趣的特性。这对固体物理学家和材料科学家提出了特殊的挑战，因为研究材料中的原子水平缺陷很困难。我们将使用中子和x射线衍射的原子对分布函数（PDF）分析技术来表征过渡金属氧化物；属于上述类别的一组重要材料。我们将使用新颖的数据分析和建模技术，由我们和其他人共同开发，从数据中提取定量结构信息，并将这些观察结果与测量的电性能相关联。其中许多材料显示出巨大的技术前景，例如高温超导体和巨大的耐磁锰矿材料，它们可能在计算机读写磁头中得到应用。我们正试图了解原子缺陷在其有趣的电学性质中所起的作用。＊＊＊

9700966 Billinge The local structure of transition metal oxides (TMOs) exhibiting interesting electronic properties will be studied using the pair- distribution function (PDF) analysis of powder diffraction data. This technique utilizes Bragg and diffuse scattering over a very wide range of momentum transfer (Q) and yields the atomic short-range order directly. It goes beyond the approximation of perfect crystallinity and allows the local structure to be solved on length-scales from 1-20 angstroms. This type of structural analysis will be applied to a variety of transition metal oxides such as high-Tc materials, layered manganites and nickelates and the colossal magnetoresistant manganites. In these materials, the structure can respond to the electronic state and we will look for correlations between changes in electrical properties and local structural effects. In this way, the nature of localized electronic states, such as polaronic, bipolaronic and charge-phase-separated states, will be elucidated. %%% The great materials scientist F.C. Franck is reported to have said "crystals are like people -- it is the defects which make them interesting". Indeed, many of the most interesting, and useful, new materials exhibit a high degree of atomic disorder; and it is often the defects which give them their interesting properties. This presents special challenges for solid state physicists and materials scientists because of the difficulty of studying atomic level defects in materials. We will be using the technique of atomic pair- distribution function (PDF) analysis of neutron and x-ray diffraction to characterize transition metal oxides; an important group of materials which fall into the above category. We will use novel data analysis and modeling techniques, developed both by us and by others, to extract quantitative structural information from the data and correlate these observations with the measured electrical properties. A number of these material s show great technological promise, such as the high-Tc superconductors and colossal magnetoresistant manganite materials which may have an application in computer read/write heads for example. We are attempting to understand the role that atomic defects play in their interesting electrical properties. ***