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. As x approached 2, a small fraction of H atoms that was located on an interstitial site other than the tetrahedral one appeared to contribute significantly to the diffusivity. The activation enthalpies for all possible jumps in a system with 2 different types of site were shown to be independent of x. The corresponding attempt frequencies were compatible with a classical diffusion mechanism.

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

The best linear fits to the solute diffusion data ([1305] to [1309], [1313] to [1314], [1317] to [1318], [1322] to [1325], [1332] to [1334]) yield:

Cr: Ln[Do] = 0.55E – 22.7 (R2 = 0.82); H: Ln[Do] = 0.17E – 8.2 (R2 = 0.32);

Mn: Ln[Do] = 0.27E – 14 (R2 = 0.97); O: Ln[Do] = 0.29E – 14.4 (R2 = 0.37);

Zr: Ln[Do] = 0.34E – 18.9 (R2 = 0.999)