Enhanced Diffusivity Along Dislocations--From Quantum Tunneling to Classical Transport in the Pd-H System

技术摘要：该项目将通过准弹性中子散射测量和第一原理计算，研究变形Pd中氢沿着位错（氢管扩散）的增强扩散率的量化。 工作范围利用最近在NSF赞助下开发的协议，以研究在非常低的浓度下的氢，并作为变形Pd中温度的函数。 实验方法使用先进的准弹性中子能谱仪在Spandex中子源和NIST中心的中子研究，并采用计算协议来模拟氢的局部应变环境中的位错（放松成两个部分位错）超晶胞。 结合实验和计算的努力将提供第一个直接量化的氢运输沿着位错的温度制度，从经典的运输（平移扩散通过网站跳跃）量子隧穿。 这项工作的主要目标是直接测量管道扩散激活能，扩散常数，量子隧穿温度制度的扩展，以及增强扩散率的物理基础，从第一原理计算位错。 第二个目标是使用相同的实验和计算方法研究晶界扩散。 该工作范围代表了美国目前先进的准弹性中子散射能力在低氢存量和低温范围内的扩展，从而为这些仪器在氢定量方面建立了新的灵敏度。非技术总结：金属中的杂质影响许多与性能和应用相关的重要特性。 金属是晶体，因为原子排列有序。 这种有序排列的破坏是常见的，称为晶格缺陷。 这项工作涉及氢，杂质和一种类型的晶格缺陷，位错的研究。 特别地，将研究金属钯中的氢和位错的相互作用，以更好地理解溶质杂质如何沿着位错晶格缺陷移动或扩散。 该项目将采用先进的计算工具和先进的中子散射仪器来实现既定目标。 工作范围代表了一个显着的扩展实验和计算方法的新制度的氢扩散行为。 预计这项研究将促进更好地理解晶格缺陷对含位错金属中氢输运的影响。这项工作的影响将超出对钯中氢的详细研究，可能影响从金属脆化到能量储存的材料科学领域。 两名研究生将接受两种研究方法的教育和培训，先进的中子散射技术和第一原理计算，这是科学探究的最前沿。 材料研究中第一性原理计算的广度是广泛的，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 SUMMARY:The project will study quantification of enhanced diffusivity of hydrogen along dislocations (hydrogen pipe diffusion) in deformed Pd via quasi-elastic neutron scattering measurements and first-principles computations. The work scope takes advantage of protocols developed recently under NSF sponsorship to study hydrogen at very low concentration and as a function of temperature in deformed Pd. The experimental methodologies use advanced state-of-the-art quasi-elastic neutron spectrometers at the Spallation Neutron Source and the NIST Center for Neutron Research and employ computational protocols to simulate hydrogen within the local strain environment of a dislocation (relaxed into two partial dislocations) supercell. The combined experimental and computational efforts will provide the first direct quantification of hydrogen transport along dislocations over a temperature regime from classic transport (translational diffusion via site hopping) to quantum tunneling. Key objectives of the work are the direct measurement of pipe diffusion activation energy, the diffusion constant, extension to the quantum tunneling temperature regime, and the physical basis for enhanced diffusivity at dislocations from first-principles computations. A secondary objective is the study of grain boundary diffusion using the same experimental and computational methodologies. The work scope represents an extension of current advanced quasi-elastic neutron scattering capabilities in the U.S. to a regime of low hydrogen inventory and low temperature, thereby establishing new sensitivities for these instruments in the quantification of hydrogen.NON-TECHNICAL SUMMARY:Impurities in metals influence many important properties related to performance and applications. Metals are crystalline in that the atoms form an ordered arrangement. Disruptions of this ordered arrangement are common and are called lattice defects. This work involves the study of hydrogen, an impurity, and one type of lattice defect, a dislocation. In particular, the interaction of hydrogen and dislocations in the metal palladium will be studied to better understand how the solute impurity moves or diffuses along the dislocation lattice defects. The project will employ advance computational tools and advanced neutron scattering instrumentation to achieve the stated goals. The work scope represents a significant extension of experimental and computational methodologies to new regimes of hydrogen diffusion behavior. It is anticipated that the research will promote an improved understanding of the influence of lattice defects on hydrogen transport in metals containing dislocations.The work will have an impact beyond a detailed study of hydrogen in palladium, potentially affecting areas of materials science ranging from embrittlement to energy storage in metal hydrides. Two graduate students will be educated and trained in two research methodologies, advanced neutron scattering techniques and first-principles computations, that are at the forefront of scientific inquiry. The breadth of first-principles computations 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.