Diffusion of the hydrogen in nanocrystalline vanadium films

Abstract

The β → α phase transition and diffusion of the hydrogen in nanocrystalline vanadium films were investigated. Films were deposited onto the glass substrate at the temperature 673 K and at room temperature. Transmission electron microscopy investigations of the structure of films showed that the averaged sizes of vanadium crystallites were 7 and 4 nm, respectively. The derivative of the electrical resistance of the saturated film revealed the broad β → α phase transition about 390 K. The diffusion coefficient of the hydrogen was obtained from the approximation of the time dependence of the increase of the electrical resistance of the non-saturated part of the film by an analytical expression. Values of the diffusion coefficient revealed the strong dependence on the concentration of the hydrogen. At small concentration of the hydrogen, the diffusion coefficient was equal to that in the bulk vanadium. At large concentrations of the hydrogen (above 20 at. %), the diffusion coefficient decreases by a thousand times. The activation energy of diffusion, calculated for samples with the large concentration of the hydrogen, is equal to (44.8 ± 0.8) kJ/mol [(0.464 ± 0.008) eV].