Hydrogen-Dislocation Interactions at Low Temperature in Deformed Pd: Spatial and Vibrational Characterization Using Neutron Scattering and Advanced Computational Techniques

技术支持：本计画利用中子散射及先进的计算技术，研究低温下变形钯中氢与位错的相互作用。该项目是金属项目最近向PI（DMR-0634336）提供的SGER赠款的后续项目。这种俘获相互作用在过去已经被几个小组研究过，但从来没有在低温下（约4K），也没有结合非弹性中子散射（INS），小角中子散射（SANS）和密度泛函理论（DFT）。研究工作将以主要研究员最近在惯性导航系统和密度泛函理论方面的工作为基础。这项工作表明：1）在位错处捕获的氢在从295 K冷却到4 K的过程中经历了块状相变，其振动态密度（DOS）可能是局部畸变的特征; 2）DFT可以用于在灵活的边界条件下弛豫Pd中的刃位错。这一初步工作为进一步实验研究氢在位错畸变环境中的行为奠定了基础。实验表征将包括用INS测量振动DOS和用SANS定量捕获氢的径向范围。实验参数空间将包括温度、氢浓度和位错亚结构的控制。计算部分的工作将产生氢的结合能在不同的网站内和附近的位错核心和振动态密度为捕获的氢。特别令人感兴趣的是测得的振动DOS与扭曲位错环境的扰动。虽然这些扰动可能是由于晶格畸变引起的，但仅凭INS和SANS测量无法最终确定其来源。一个直接的，第一性原理计算的捕获氢振动DOS在一个放松的晶格是必要的。非技术性：该研究的教育价值与中子散射技术和先进计算方法的联合应用有关，以研究这些捕获相互作用。PI具有开展工作所需的专门知识，INS和DFT的初步工作为进一步调查提供了合理的基础。预计这项研究将促进对扭曲晶格环境中氢行为的更好理解。这项工作将产生的影响超出了详细研究氢捕获在位错在钯。两名研究生将接受两项研究协议的教育和培训，中子散射和先进的计算技术处于科学探究的最前沿。DFT在材料研究中的广度是广泛的，NIST，ORNL和LANL最近对中子散射基础设施的投资也是如此。在使用这些协议的培训研究生将很好地定位为生产性的科学事业。

TECHNICAL: This project focuses on studying of hydrogen-dislocation trapping interaction at low temperature in deformed Pd using neutron scattering and advanced computational techniques. This project is a follow up of a recent SGER grant to PI (DMR-0634336) from the Metals program. This trapping interaction has been studied in the past by several groups, but never at low temperature (to about 4K), nor with a combination of inelastic neutron scattering (INS), small-angle neutron scattering (SANS), and density functional theory (DFT). The research effort will be based on recent INS and DFT work by the PIs. This work demonstrates 1) that hydrogen trapped at dislocations undergoes a bulk-like phase transformation during cooling from 295 K to 4 K, with a vibrational density of states (DOS) that may be a signature of local distortion and 2) that DFT can be used to relax an edge dislocation in Pd with flexible boundary conditions. This initial work provides a foundation for further experimental study of the behavior of hydrogen in the distorted environment of dislocations. The experimental characterization will include the measurements of the vibrational DOS with INS and quantification of the radial extent of the trapped hydrogen with SANS. The experimental parameter space will include temperature, hydrogen concentration, and control of the dislocation substructure. The computational component of the work will yield the hydrogen binding energy at different sites within and near the dislocation core and the vibrational DOS for trapped hydrogen. Of particular interest are perturbations of the measured vibrational DOS with the distorted dislocation environment. Although these perturbations are likely due to lattice distortion, the INS and SANS measurements alone cannot conclusively identify their origin. A direct, first-principles calculation of the trapped hydrogen vibrational DOS in a relaxed lattice is necessary. NON-TECHNICAL: The education merit of the research is related to the combined application of neutron scattering techniques and advanced computational methods to study these trapping interactions. The PIs have the expertise required to perform the work, and the preliminary INS and DFT work provides a reasonable basis for further investigation. It is anticipated that the research will promote an improved understanding of the behavior of hydrogen in distorted lattice environments. The work will have an impact beyond a detailed study of hydrogen trapping at dislocations in Pd. Two graduate students will be educated and trained in two research protocols, neutron scattering and advanced computational techniques that are at the forefront of scientific inquiry. The breadth of DFT in materials research is extensive, as are the recent investments in neutron scattering infrastructure at NIST, ORNL, and LANL. Graduate students trained in the use of these protocols will be well positioned for productive scientific careers.