Ab initio study of He, Ne, Ar, Kr incorporation in zirconium carbide

Abstract

Due to the potential utilization of ZrC in advanced nuclear reactors, it is important to understand the behavior of intrinsic defects and fission gas products. In this study, the energetics of intrinsic defects (i.e. monovacancy, self-interstitial, anti-site defect, Frenkel pair, Schottky defect and divacancy), the incorporation and migration of single noble gas atom (Ng = He, Ne, Ar and Kr), the atomic configuration of small noble gas clusters (Ngn) and Ngn-vacancies complexes have been systemically investigating by ab initio calculations. Carbon atoms escape from the lattice site easily and then form vacancy, interstitial or Frenkel pairs, while the formations of Zr vacancy and interstitial cost more energy and the presence of Zr vacancy would induce a new C vacancy along <100> direction. Due to the higher formation energy, anti-site defects are not expected to be the dominant defect in ZrC. The formation energy of Ng atom increases linearly with the atomic numbers (thus atomic radius) of Ng; meanwhile, the lattice distortion is also more pronounced. The lowest diffusion barrier of Ng atom is found on the path from one interstitial site to an adjacent one along <100> direction. The nearest distance and the corresponding binding energy between Ng-Ng pair gradually increase with the atomic radius, meaning that Ng atoms tend to aggregate in ZrC crystal. In addition, existence of the monovacany, divacancy and Schottky defect (especially Zr vacancy) considerably reduces the formation energies of Ngn clusters.