Effects of vacancies on the behavior of H in ZrC: A first-principles study

Abstract

Understanding the response of ZrC to irradiation damage is crucial for the successful implementation of ZrC materials in the new generation of nuclear reactors. In this study, we systematically investigate the behavior of single H atom, small H_n clusters (n = 2–4), vacancies, and H-vacancy complexes in ZrC host lattice using first-principles calculations. Energetically, we find that H at the tetrahedral site surrounded by one C atom and three Zr atoms (I_Hb) is more favorable than at the cube center site (I_Ha). H_C in ZrC exhibits the highest stability, followed by I_Hb, I_Ha, H_Zr. The average formation energy of per H in H_n cluster increases with the number of H atoms and two interstitial H atoms tend to exclude each other. Additionally, the average formation energy per H of H_n clusters inside ZrC supercell with vacancies is lower than that inside perfect ZrC supercell. Combined the binding energy, the vacancies will promote the aggregation of H atoms. V_Zr exhibits a greater capacity for hydrogen accommodation in comparison to V_C, attributed to its larger vacant sites. The generally decreasing binding energy between H and H-vacancy complexes suggests that the attraction weakens and can even turn into repulsion as the number of H atoms increases.