Proton magnetic resonance absorption spectra of YH2+x, with x = 0.10, were recorded at 4.2 to 310K and 36.01MHz and at 150 to 400K and 299.8MHz. The evidence for proton self-diffusion followed from changes in line-width with temperature. The second moment of the resonance lines was determined from the experimental spectra and was compared with values calculated from crystallographic data. The averaging effect of diffusion on the second moment was taken into account using Monte Carlo simulations of the diffusion process. The simulation was performed for a 5 x 5 x 5 block of unit cells with periodic boundary conditions. The fitting parameters were the attempt frequency ν0 and the activation energy Ea for hydrogen diffusion, assuming an Arrhenius behavior of the jump frequencies. The Monte Carlo simulations were performed for tetrahedral-octahedral exchanges while direct tetrahedral-tetrahedral jumps were neglected, for simplicity. Three models of hydrogen diffusion, differing in the maximum jump lengths allowed for a given model, were considered. These lengths were taken to be the distances from hydrogen attempting to jump to the first- (1NN), second- (2NN), and third- (3NN) nearest neighbor position able to accept the jumping atom. Assuming a given attempt frequency of 6.0 x 1012/s for all three models, the activation energies which gave the best fit to experimental data were 0.5, 0.54 and 0.55eV for 1NN, 2NN, and 3NN models, respectively.

Van Vleck Second Moments and Hydrogen Diffusion in YH2.1 - Measurements and Simulations. R.Goc, O.J.Zogał, A.H.Vuorimäki, E.E.Ylinen: Solid State Nuclear Magnetic Resonance, 2004, 25[1-3], 133-7