Samples of ZrHx, with x-values of 1.58 to 1.98, were studied at 600 to 970K by using pulsed field gradient nuclear magnetic resonance techniques. It was found that the activation enthalpy for H diffusion increased sharply as x approached a limiting value of 2:

x = 1.58:     D (cm2/s) = 1.53 x 10-3 exp[-0.61(eV)/kT]

x = 1.79:     D (cm2/s) = 1.06 x 10-3 exp[-0.64(eV)/kT]

x = 1.86:     D (cm2/s) = 8.00 x 10-4 exp[-0.67(eV)/kT]

x = 1.93:     D (cm2/s) = 6.54 x 10-3 exp[-0.88(eV)/kT]

x = 1.98:     D (cm2/s) = 8.20 x 10-2 exp[-1.10(eV)/kT]

It was deduced that the H atoms jumped predominantly between nearest-neighbor tetrahedral sites. However, the observed concentration dependences of the activation enthalpy and the pre-exponential factor suggested that, at high H concentrations and high temperatures, an additional interstitial site was occupied.

G.Majer, W.Renz, R.G.Barnes: Journal of Physics - Condensed Matter, 1994, 6[15], 2935-42