HYDROGEN DIFFUSION IN HCP Zr

We study the behavior of hydrogen (H) in theαandβphases of Zr and in theβphase of Nb, using the Siesta andVasp first principles codes based on the density functional theory (DFT). We calculate the hydrogen solution energy, the binding energy of the H-H and H-Nb complexes, as well as, the mixing energy of the Zr-Nb system. Furthermore, we have proposed a simple model for the study of the hydrogen diffusion (DH) mediated by interstitial mechanism in hcp Zr. We find that interstitial hydrogen diffuses isotropically according to DH=1.1×10−7exp(−42 KJ.mol−1/RT)(m2/s). Our results are in good agreement with experimental data and other Kinetic Monte Carlo (KMC) calculations. Finally, the formation energies of the three most stable hydrides in the hcp Zr phase were also calculated.