Structure and Entropy of Materials Studied by Nuclear Resonant Scattering

本研究的目的是发展可靠和准确的技术，用于确定复杂材料的结构和振动特性。 研究的一个主要目标是利用穆斯堡尔衍射独特的化学环境选择性来研究金属合金中的无序。该技术的独特之处在于它能够在特定的化学环境中选择铁原子，并仅从这些铁原子中获得衍射图案。利用新的穆斯堡尔衍射仪，可以测量有序FeAl中具有3个铝第一近邻的铁原子的不规则化学位的周期性。我们也将对FeRh和PdFe的合金进行研究，重点是研究非弹性光谱，以获得铁原子的声子分态密度。使用金刚石对顶砧的极高压力将用于研究压力对原子间力常数的影响。在另一个不同类型的实验中，穆斯堡尔衍射仪将被用来研究磁性纳米颗粒中热弛豫的空间尺度。在工作过程中，将开发一个关于赤铁矿纳米颗粒热弛豫的具体实验。这些结果表明了合金的振动熵如何依赖于原子间的分离，并可以解释铁合金的P（V，T）状态方程的原因。这项工作的广泛影响不仅在于开发复杂材料结构测定的可靠技术，而且还在于获得原子水平上固体相互作用的详细信息。热力学和原子排列是材料科学的核心，这项工作将应用新的实验方法来研究它们。这些方法是专门的，但具有独特的能力，可以解决有关材料结构和动力学的高层次细节。物质的结构是穆斯堡尔衍射工作的重点。物质的熵是核非弹性共振散射研究的焦点。衍射和散射的基本问题在材料科学中也具有广泛的学术兴趣。

The objective of this research is the development of reliable and accurate techniques for the determination of structural and vibrational properties of complex materials. A major goal of the study is to investigate the disorder in metallic alloys with the unique chemical environment selectivity of Mossbauer diffractometry. The unique feature of the technique is its capability to select iron atoms in a particular chemical environment, and obtain a diffraction pattern from those iron atoms alone. With the new Mossbauer diffractometer, it is possible to measure the periodicity of an irregular chemical site of iron atoms with 3 aluminum first-nearest neighbors in ordered FeAl. Studies will also be made on alloys of FeRh and PdFe with emphasis on investigating the inelastic spectra to obtain the phonon partial density of states of iron atoms. Extreme high pressures using diamond anvil cells will be used to investigate the influence of pressure on interatomic force constants. In a different style of experiment, the Mossbauer diffractometer will be used to study the spatial scale of thermal relaxations in magnetic nanoparticles. A specific experiment on thermal relaxations on hematite nanoparticles will be developed over the course of the work. Such results show how the vibrational entropy of alloys depends on interatomic separations, and can elucidate the reasons for the P(V,T) equation of state of iron alloys. The broader impact of the proposed work lies not only in developing reliable techniques for the structural determination of complex materials but also in obtaining detailed information on interactions in solids at the atomic level.Thermodynamics and atom arrangements are at the core of materials science, and the proposed work will apply new experimental methods for studying them. The methods are specialized, but have unique capabilities for resolving a high level of detail about the structure and dynamics of materials. The structure of materials is the focus of the work on Mossbauer diffractometry. The entropy of materials is the focus of the work on inelastic nuclear resonant scattering. The basic issues in diffraction and scattering are also of broad academic interest in materials science.