NMR study of hydrogen diffusion in zirconium hydride

The nuclear-magnetic-resonance method was used to study the diffusion of hydrogen in zirconium hydride by measuring the temperature dependence of $T_1$ in a temperature range where the major relaxation mechanism was due to hydrogen diffusion. The samples investigated were ${\mathrm{ZrH}}_{1.588}$, ${\mathrm{ZrH}}_{1.629}$, ${\mathrm{ZrH}}_{1.684}$, ${\mathrm{ZrH}}_{1.736}$, ${\mathrm{ZrH}}_{1.815}$, ${\mathrm{ZrH}}_{1.910}$, and ${\mathrm{ZrH}}_{1.960}$. These spanned both the cubic and tetragonal phases. The activation energy was found to be independent of hydrogen concentration in the cubic phase with $E_a$=13.4±0.4 kcal/mol and a preexponential factor given by A=(1/2)(2-x)(45±10)×${10}^{12}$ Hz. In the tetragonal phase the activation energy of the bulk of the hydrogen increased modestly with concentration. In addition, it was discovered that a new very fast hydrogen channel was created by the tetragonality for ∼3% of the hydrogen. They jump with a preexponential factor that is about 2 orders of magnitude larger than that of the rest of the hydrogen. A comparison was also made between the Bloembergen-Purcell-Pound, the Barton-Sholl, and the Bustard theories for nuclear magnetic relaxation due to diffusion.