RUI: Simulation and Improved Analysis of Data from PAC and other Hyperfine Methods for Studying Local Atomic Jumps and Long Range Diffusion in Intermetallic Compounds

RUI：对 PAC 和其他超精细方法的数据进行模拟和改进分析，用于研究金属间化合物中的局部原子跳跃和长程扩散

• 批准号: 0606006
• 负责人: Matthew Zacate
• 金额: $ 10.99万
• 依托单位: Northern Kentucky University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-06-01 至 2010-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0606006&HistoricalAwards=false
• 关键词: RUI; Simulation; Improved; Analysis; Data

TECHNICAL: Hyperfine methods such as Nuclear Magnetic Resonance, Mossbauer, and Perturbed Angular Correlation (PAC) spectroscopies are sensitive to changes in electronic and magnetic structure within about 1 nm of the probe atoms that are used by the techniques. Hyperfine methods are therefore capable of detecting local atomic jumps. As a consequence, hyperfine methods have the potential to allow researchers to determine operative diffusion mechanisms in ordered alloys and to study atomic motion in nanocrystalline materials. At present, complications in analysis of data obtained by the hyperfine methods hold back widespread application of these techniques in studies of diffusion. The complications arise in the development of stochastic models that connect jumping of atoms to the time varying interactions they induce. PIs will expand on the approach set forth by Winkler and Gerdau to integrate the calculation of theoretical spectra for the hyperfine methods. In the past, constraints on computational power have required researchers who use Winkler and Gerdau's approach to perform time consuming activities such as (1) reducing large matrices analytically using symmetry arguments or (2) developing analytic approximations to numerical solutions of matrix eigenproblems. Modern computers are powerful enough that one can now incorporate numerical solution of the stochastic models directly into least-squares-fitting software for analyzing spectra directly from the stochastic model. Computer code that is sufficiently general to support stochastic models for all types of hyperfine interactions and for nuclei with any spin state will be developed, and aid cyberinfrastructure (CI) development. The code will allow calculation of theoretical spectra for the hyperfine methods that can be used in least-squares-fits of experimental data. In addition to helping in data analysis, the computer code will support simulation of spectra under varying experimental conditions such as for different crystal structures, defect models, compositions, temperatures, and diffusion mechanisms. A significant portion of the proposed work will utilize simulations to determine under what experimental conditions one can use hyperfine methods to distinguish one type of diffusion mechanism from another in ordered alloys. NON-TECHNICAL: The movement of atoms in solids is of fundamental importance in selection and processing of materials. While the emphasis of this work will be on diffusion in intermetallic compounds, the ability to quickly develop stochastic models for analysis and simulation of diffusion would benefit researchers interested in ceramic and semiconducting materials as well. Moreover, it would be beneficial for studies of atomic motion in nanoparticles and for studies of spin fluctuations.

技术：超精细方法，如核磁共振、穆斯堡尔光谱和摄动角相关（PAC）光谱，对这些技术所使用的探针原子约1nm内的电子和磁性结构的变化很敏感。因此，超精细方法能够检测到局部原子跳变。因此，超精细方法有可能使研究人员确定有序合金中的有效扩散机制，并研究纳米晶体材料中的原子运动。目前，超精细方法获得的数据分析的复杂性阻碍了这些技术在扩散研究中的广泛应用。在将原子的跳跃与它们所引起的时变相互作用联系起来的随机模型的发展中出现了复杂性。pi将扩展Winkler和Gerdau提出的方法，以整合超精细方法的理论光谱计算。在过去，计算能力的限制要求使用Winkler和Gerdau方法的研究人员执行耗时的活动，例如(1)使用对称参数解析地减少大型矩阵或(2)开发矩阵特征问题数值解的解析近似。现代计算机已经足够强大，人们现在可以将随机模型的数值解直接合并到最小二乘拟合软件中，以便直接从随机模型中分析光谱。将开发出足够通用的计算机代码，以支持所有类型的超精细相互作用和具有任何自旋态的原子核的随机模型，并帮助网络基础设施（CI）的发展。该代码将允许计算理论光谱的超精细方法，可用于最小二乘拟合的实验数据。除了有助于数据分析之外，计算机代码还将支持在不同实验条件下的光谱模拟，例如不同的晶体结构、缺陷模型、成分、温度和扩散机制。所提出的工作的很大一部分将利用模拟来确定在什么实验条件下可以使用超精细方法来区分有序合金中一种类型的扩散机制。非技术：固体中原子的运动在材料的选择和加工中具有根本的重要性。虽然这项工作的重点将放在金属间化合物的扩散上，但快速开发用于分析和模拟扩散的随机模型的能力也将使对陶瓷和半导体材料感兴趣的研究人员受益。此外，它将有利于研究纳米粒子中的原子运动和研究自旋涨落。