Defects and Diffusion in Intermetallic Compounds

使用γ射线的扰动角相关（PAC）研究金属间化合物中的柯林斯点缺陷，PAC是一种光谱技术，提供固体中探针原子的不同局部环境的优异分辨率。在靠近铟探针原子的原子壳层中检测到属于高阶平衡缺陷的晶格空位和反位缺陷。最令人感兴趣的平衡缺陷是使扩散成为可能的高温缺陷，例如二元合金中的肖特基空位对。本项目的主要目的有三：（1）通过对淬火样品和高温样品的测量，确定平衡缺陷的性质。所选的二元合金具有B2（CsC1）结构，包括高温结构铝化物，如NiAl和模型系统，如PdIn和AuCd，其中PAC探针的干扰最小。首次由高温空位运动引起的PAC信号的核弛豫确定了空位迁移谱。(2)本文研究了三元化合物AuAgCd_2中Au和Ag原子间的有序性。由于序参量是局部确定的，因此对序参量波动的敏感性比使用常规衍射方法时大得多。如果发现过渡是二阶的，测量可以深入了解导致有序的相互作用的范围。(3)使用PAC来确定空位浓度和量热法来确定存储的能量的部分与晶格空位在机械研磨PdIn检查。到目前为止，还没有足够的知识过剩的能量是如何存储在材料在铣削过程中，本研究的目标是确定存储在空位的能量。在这里研究的材料缺陷影响相稳定性和扩散在各种应用中使用的先进材料。***

9612306 Collins Point defects in intermetallic compounds are investigated using perturbed angular correlations of gamma rays (PAC), a spectroscopy technique providing excellent resolution of different local environments of probe atoms in solids. Lattice vacancies and antisite defects belonging to higher- order equilibrium defects are detected in atomic shells close to indium probe atoms. The equilibrium defect of greatest interest is the high-temperature one that makes diffusion possible, such as the Schottky vacancy-pair in a binary alloy. There are three objectives to the grant: (1) Properties of equilibrium defects are determined through measurements on quenched samples and samples at high temperature. Binary alloys selected have the B2 (CsC1) structure, including high-temperature structural aluminides, such as NiAl and model systems such as PdIn and AuCd in which disturbances from PAC probes are minimal. For the first time vacancy migration enthalpies are determined from nuclear relaxation of PAC signals caused by vacancy motion at high temperature. (2) A study is made of ordering among Au and Ag atoms in the ternary compound AuAgCd2. Because the order parameter is determined locally, there is a much greater sensitivity to order-parameter fluctuations than found when using conventional diffraction methods. If the transition is found to be second-order, the measurements give insight into the range of interactions leading to the ordering. (3) The fraction of stored energy associated with lattice vacancies in mechanically-milled PdIn is examined using PAC to determine vacancy concentrations and calorimetry to determine the stored energy. To date there is inadequate knowledge of how excess energy is stored in materials during milling, and the goal of this study is to determine the amount of energy stored in vacancies. %%% The material defects under study here affect phase stability and diffusion in advanced materials used in a variety of applic ations. ***