Proceedings of the Third International Conference on Metals & Hydrogen E04

Thermodynamic versus kinetic origin of Super Abundant Vacancy formation in Ni single crystals in presence of hydrogen

Arnaud METSUE (1)1 , Abdelali OUDRISS (1)1 , Xavier FEAUGAS (1)1

  • (1) 1

    Laboratoire des Sciences de l’Ingénieur pour l’Environnement, UMR CNRS 7356 Université de La Rochelle, Avenue Michel Crépeau, 17000 La Rochelle, France


The aim of this study is a clarification of the thermodynamic and/or kinetic origin of the formation of superabundant vacancies in nickel exposed to hydrogen. Here, we have conducted first principles calculations within DFT on the solubility and diffusion of H in Ni single crystals both in the bulk material and in the vicinity of a vacancy core up to PH2=10 GPa. The calculations are performed up to 1200 K where the Gibbs free energies of H solubility, H-vacancy clusters formation and diffusion’s barriers are expressed as a sum of vibration and electronic contributions from the computation of the phonon dispersion curves and the electronic density of states. In a first time, we determine the total H solubility and the total vacancy concentration of H-free and H-decorated defects at thermodynamic equilibrium from the minimization of the free energy of the system expressed in the grand-canonical ensemble. We find that the total vacancy concentration at thermodynamic equilibrium is too small compared to the concentrations observed experimentally. In a second time, we calculate the H jump frequencies associated to the diffusion in the bulk lattice, the trapping and the detrapping of the solute into and out of the vacancy core. These jump rates are implemented in a kinetic model to follow the evolution of mobile H and the formation of H-vacancy clusters during H diffusion. We find that the H-vacancy clusters concentrations become larger than the values given by the equilibrium condition. This result indicates that the system switch into an out-of-equilibrium state and may be responsible of the formation of superabundant vacancies. Therefore, we suggest that the formation of superabundant vacancies in nickel has mainly a kinetic origin from the oversaturation of H-decorated defects during diffusion.


  • nickel
  • hydrogen
  • first-principles calculations
  • super abundant vacancies
  • diffusion coefficients
  • solubility.