Defects and Diffusion in Intermetallic Compounds

用微扰角相关伽马射线谱技术研究了金属间化合物中的9612306个柯林斯点缺陷，这是一种能很好地分辨固体中探测原子的不同局部环境的光谱技术。在接近铟探针原子的原子壳层中发现了属于高阶平衡缺陷的晶格空位和反位缺陷。人们最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。该基金有三个目标：(1)通过对淬火样品和高温样品的测量来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和模型体系，如PdIn和AuCd，其中来自PAC探针的干扰最小。首次从高温下空位运动引起的PAC信号的核弛豫确定了空位迁移热。(2)研究了AuAgCd2三元化合物中Au、Ag原子间的有序性。由于序参数是局部确定的，因此对序参数涨落的敏感性比使用传统的衍射法时要高得多。如果发现这种转变是二级的，这些测量就能洞察导致有序的相互作用的范围。(3)用PAC测定空位浓度，用量热法测定机械球磨PdIn中与晶格空位有关的储能。到目前为止，对于在研磨过程中多余的能量是如何储存在材料中的了解还不充分，本研究的目的是确定储存在空位中的能量的量。这里研究的材料缺陷会影响在各种应用中使用的先进材料中的相稳定性和扩散。***

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. ***