氧、氢和碳原子在α­铀（001）表面吸附与扩散特性的第一性原理研究

摘要

The adsorption and diffusion properties of O, H and C atoms on α­U(001) surface were studied by first­principles density functional theory approach. For the on­surface adsorption, O and H atoms prefer to occupy the H2 site, while C atoms tend to occupy the H1 site. The diffusion barrier of O atom on U surface is low and the diffusion is easy, which will lead to the formation of uranium­oxidation layer on the top of surface. The diffusion barrier of H atom is larger and that of C atom is the largest one, thus it is difficult for C atom diffusion on the U surface. As for the diffusion of atom from the surface site to the sub­surface, the barriers of H and C atoms are low, while that of O atom is very high, which indicates that the O atom can not migrate into the next surface. And the barrier of C atom diffusion to the sub­surface is reduced by about 0.5 eV with the assistance of O atom nearby. The U­O oxidation layer on the surface and the U­C layer on the sub­surface can be formed easily, which help to prevent the metallic U from further oxidation. These results agree good with available experiments.%　　应用第一性原理密度泛函理论系统研究氧、氢和碳原子在α­铀(001)表面的吸附与扩散特性。研究发现：在铀表面氧原子与氢原子择优吸附在 H2位置，碳原子倾向于占据在 H1位置；氧原子在铀表面的扩散势垒较低，容易在铀表面上扩散，形成表面氧化层；氢原子的扩散势垒较高，碳原子的扩散势垒最大，难以在表面扩散。吸附原子从铀表面向次表面层扩散时，氧原子的扩散势垒很高，难以向次表面扩散；碳和氢原子的扩散势垒较低，特别是在氧的辅助作用下，碳原子向次表面的扩散势垒降低约0.5 eV，使碳原子易于向次表面层扩散；铀表面上会形成氧化层，次表面会形成富碳层，可对铀的进一步氧化起到抑制作用，这与相关实验结果符合较好。