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

技术：本项目主要利用中子散射和先进的计算技术研究变形钯中低温氢-位错俘获相互作用。该项目是最近SGER授予金属项目PI （DMR-0634336）的后续项目。过去已经有几个研究小组对这种俘获相互作用进行了研究，但从未在低温（约4K）下进行过研究，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）进行过研究。研究工作将以pi最近的INS和DFT工作为基础。这项工作证明了1)位错处的氢在295 K到4 K的冷却过程中经历了块状相变，具有可能是局部畸变的振动态密度（DOS）， 2) DFT可以用于在柔性边界条件下放松Pd中的边缘位错。这一初步工作为进一步实验研究氢在位错扭曲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量化捕获氢的径向范围。实验参数空间将包括温度、氢浓度和位错子结构的控制。本工作的计算部分将得到位错核内和附近不同位置的氢结合能以及被困氢的振动DOS。特别令人感兴趣的是测量的振动DOS与畸变位错环境的扰动。虽然这些扰动很可能是由于晶格畸变，但INS和SANS的测量结果不能单独确定它们的起源。一个直接的，第一性原理计算被困氢在松弛晶格中的振动DOS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结合应用有关，以研究这些捕获相互作用。pi拥有执行工作所需的专业知识，而初步的INS和DFT工作为进一步调查提供了合理的基础。预计该研究将促进对氢在扭曲晶格环境中的行为的更好理解。这项工作的影响将超出对Pd中位错处氢捕获的详细研究。两名研究生将接受两项研究方案的教育和培训，即中子散射和先进的计算技术，这是科学探究的前沿。DFT在材料研究中的广度是广泛的，正如NIST、ORNL和LANL最近对中子散射基础设施的投资一样。在使用这些协议方面受过训练的研究生将为富有成效的科学事业做好准备。

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.