First-principles study of native point defects and diffusion behaviors of helium in zirconium carbide

The potential native point defects and diffusion behaviors of helium impurities in zirconium carbide (ZrC) are discussed by first-principles calculations. It is found that C-related defects are easier to form in energy than Zr-related defects, consistent with experimental observations. By comparing incorporation energies at various sites, the energetically favored location for helium in intrinsic ZrC is determined to be the Zr substitution site. The positive but small incorporation energy suggests that helium is at the edge of solubility in ZrC. It is revealed that Zr-vacancy assisted diffusion mechanism for helium plays a dominant role in ZrC system with a small energy barrier of 0.70 eV. Besides, helium is likely trapped in Zr pre-existing vacancies, which may impact on the mechanical properties and dimensional stability of ZrC materials.