Proton andSc45nuclear-magnetic-resonance study of hydrogen diffusive hopping in hcp scandium

The activation energy $E_a$ (0.54±0.01 eV) and attempt frequency ${\nu }_0$ (1×${10}^{14}$Hz±50%) of hydrogen diffusive hopping in dilute solid solution in hcp Sc metal (α-${\mathrm{ScH}}_{\mathrm{x}}$) have been determined from NMR measurements of the temperature dependence of the spin-lattice relaxation rates of both proton and ${}_{}{}^{45}{}_{}{}^{}\mathrm{Sc}$. For low hydrogen concentrations (x≤0.11), the results are in excellent agreement with expectations based on inelastic neutron scattering measurements on the closely similar Y-H system. The absence of a prefactor anomaly, in particular in the proton results, is consistent with repulsive particle-particle interactions at the saddle point being responsible for such anomalies.