Using a first-principles method, dissolution and diffusion of hydrogen in molybdenum were investigated. It was shown that a single H atom was energetically favorable when sited at the tetrahedral interstitial position rather than the octahedral interstitial and diagonal interstitial positions. This can be confirmed by the electron localization function result. Bader charge analysis suggested that the bonding between H and surrounding Mo was mainly ionic, plus a slight covalent component. Double H atoms tended to be paired up at the two neighboring tetrahedral interstitial sites along the <110> direction: with a distance of ∼0.221nm and a binding energy of 0.03eV. This suggested a weak attractive interaction between H atoms, with the implication that self-trapping of H and the formation of H2 molecules were quite difficult in an intrinsic Mo environment. It was demonstrated that the diffusion barrier to H jumps between the tetrahedral interstitial sites was 0.16eV, and that the dissolved concentration of H in intrinsic Mo was 2.6 x 10-8 at a typical temperature of 600K. The diffusion coefficients of H, D and T were different, due to the differing masses, and were calculated to be 1.3 x 10-7, 9.2 x 10-8 and 7.5 x 10-8m2/s at 600K.

First-Principles Study on Dissolution and Diffusion Properties of Hydrogen in Molybdenum. C.Duan, Y.L.Liu, H.B.Zhou, Y.Zhang, S.Jin, G.H.Lu, G.N.Luo: Journal of Nuclear Materials, 2010, 404[2], 109-15