Diffusion in Rare Earth Binary and Ternary Intermetallics Studied using PAC

使用 PAC 研究稀土二元和三元金属间化合物中的扩散

• 批准号: 0904096
• 负责人: Gary Collins
• 金额: $ 40.5万
• 依托单位: Washington State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-08-01 至 2013-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0904096&HistoricalAwards=false
• 关键词: Diffusion; Rare; Earth; Binary; Ternary

TECHNICAL SUMMARY:Professor Collins and coworkers pioneered use of perturbed angular correlation spectroscopy (PAC) to measure diffusional jump frequencies of probe atoms in highly ordered intermetallic compounds. Jumps are detected via relaxation of the nuclear quadrupole interaction caused by stochastic fluctuations in either the orientation or magnitude of electric field gradients (EFG). The method has been applied especially to ?line compounds? formed from rare earth and trielide elements (Al, Ga, In). Exceptionally high frequencies have been observed that are attributed to rapid motion of vacancies. Diffusion mechanisms have also been elucidated experimentally by making measurements on pairs of samples of binary alloys having the opposing boundary compositions. Comparison of measured jump frequencies has been used to identify the type of vacancy (rare-earth or trielide) that is predominantly responsible for diffusion. PAC experiments are proposed for a range of binary, pseudo-binary and ternary line compounds. Examples include Al4Ba, in which the EFGs at all sites are collinear, the pseudo-binary compounds In3(La1-xPrx), which all have the L12 structure, and LaCoIn5, a ternary phase that is structurally related to In3La. Short term collaborations have been arranged to check the extent to which jump frequencies of Cd impurity atoms and In host atoms differ.NON-TECHNICAL SUMMARY:Diffusion, or atom movement, in solids is important for understanding the mechanical strength and stability of materials and affects many other properties, such as the degree of crystalline order and magnetism. Increasingly complex materials are becoming important to technology and there is great interest in improving our understanding of diffusion phenomena in those materials. Professor Collins and coworkers have pioneered use of a spectroscopy derived from nuclear physics to directly measure frequencies of jumping of probe atoms in highly-ordered compounds. In most solids, atoms move by hopping into vacancies (missing atoms). Unusually high jump frequencies have been found in certain classes of intermetallic compounds. By comparing measurements made on two samples having slightly different compositions, Collins and coworkers have been able to determine whether the vacancy on sites of element A or element B is most responsible for diffusion. This has given an entirely new kind of insight into diffusion phenomena. Studies are proposed on a range of binary and ternary compounds. The project will involve participation and training of graduate and undergraduate students. More than 12 graduate, undergraduate and high-school students participated in research under a previous grant, including six women. Results will be disseminated widely in publications and in conference presentations and seminars. Also, short courses are planned on defects and diffusion and on use of nuclear methods to study solids. A collaboration has been established to carry out some experiments at CERN, the European nuclear physics center in Geneva, that are not possible in the US.

技术概要：柯林斯教授及其同事率先使用扰动角相关光谱（PAC）来测量高度有序的金属间化合物中探针原子的扩散跳跃频率。跳跃检测通过松弛的核四极相互作用所造成的随机波动的方向或幅度的电场梯度（EFG）。该方法已应用于特别是？线化合物？由稀土和三烯化物元素（Al、Ga、In）形成。观察到异常高的频率归因于空位的快速运动。通过对具有相反边界成分的二元合金样品对进行测量，也已经在实验上阐明了扩散机制。测量的跳跃频率的比较已被用来确定类型的空位（稀土或trielide），主要是负责扩散。 PAC实验提出了一系列的二元，伪二元和三元线化合物。例子包括Al 4 Ba，其中所有位置的EFG都是共线的，伪二元化合物In 3（La 1-xPrx），它们都具有L12结构，以及LaCoIn 5，一种结构上与In 3La相关的三元相。短期合作已安排检查的程度，其中镉杂质原子和在主机atomic.Non-Technical摘要跳跃频率：扩散，或原子运动，在固体中是很重要的理解材料的机械强度和稳定性，并影响许多其他属性，如结晶秩序和磁性的程度。越来越复杂的材料变得越来越重要的技术，有很大的兴趣，以提高我们的理解这些材料中的扩散现象。柯林斯教授和同事们率先使用核物理学中的光谱学来直接测量高度有序化合物中探针原子的跳跃频率。在大多数固体中，原子通过跳跃进入空位（缺失的原子）而移动。在某些种类的金属间化合物中发现了不寻常的高跳跃频率。通过比较两个成分略有不同的样品的测量结果，柯林斯和同事们已经能够确定元素A或元素B位置上的空位是否是扩散的主要原因。这使我们对扩散现象有了一种全新的认识。 研究提出了一系列的二元和三元化合物。该项目将涉及研究生和本科生的参与和培训。超过12名研究生、本科生和高中生参加了先前赠款下的研究，其中包括6名妇女。结果将在出版物、会议介绍和研讨会上广泛传播。此外，还计划开设关于缺陷和扩散以及利用核方法研究固体的短期课程。双方已经建立了合作关系，在位于日内瓦的欧洲核子物理中心CERN进行一些在美国无法进行的实验。