Capture and Diffusion of Hydrogen in Tantalum and Copper with Vacancy Defects: A First-Principles Study

Oxygen-free copper is utilized in nuclear processing heaters; however, it exhibits poor resistance to hydrogen radiation corrosion. A tantalum-copper diffusion layer with high vacancy concentration was prepared on the copper surface. This layer demonstrates superior hydrogen trapping and diffusion resistance compared to pure tantalum, though the underlying mechanism remains unclear. First-principles DFT methods were employed to investigate the absorption of hydrogen atoms by tantalum and copper vacancies, forming vacancy-hydrogen complexes, and their diffusion characteristics. These were compared with interstitial configurations. The ground state formation energy is lowest when a tantalum vacancy captures six hydrogen atoms. It can accommodate up to 12 hydrogen atoms while maintaining a higher energy than the interstitial configuration, forming a spherical structure with special symmetry. For copper vacancies, the formation energy remains higher than the interstitial configuration when capturing up to six hydrogen atoms. The high-vacancy diffusion layer exhibits a strong hydrogen trapping capacity. Posthydrogen capture, the overall migration energy for both tantalum and copper vacancies exceeds 2.5 eV. The energy barrier for individual hydrogen atom diffusion outward is higher than in interstitial cases when capturing up to six hydrogen atoms. Vacancies capturing hydrogen atoms play a role in maintaining the stability of hydrogen in its ground state.