45ScNMR and high-resolution quasielastic neutron scattering studies of localized H(D) motion inα−ScHx(Dx)

Abstract

Nuclear magnetic resonance measurements of the ${}^{45}\mathrm{Sc}$ spin-lattice relaxation rates in the solid solutions $\ensuremath{\alpha}\ensuremath{-}{\mathrm{ScD}}_{0.05},$ $\ensuremath{\alpha}\ensuremath{-}{\mathrm{ScD}}_{0.22},$ and $\ensuremath{\alpha}\ensuremath{-}{\mathrm{ScH}}_{0.27}$ have been performed over the temperature range 4.2--299 K and the resonance frequency range 11--86.2 MHz. For all of the samples studied, the ${}^{45}\mathrm{Sc}$ relaxation rate shows a peak near 100 K resulting from the electric quadrupole interaction modulated by localized hopping of H(D) atoms. In addition to the strong effect of isotope $(\mathrm{H}\ensuremath{\leftrightarrow}\mathrm{D})$ substitution on the amplitude of this peak, with a larger peak appearing in the deuterides, we have found that in the region of the peak, the frequency dependence of the ${}^{45}\mathrm{Sc}$ relaxation rate for $\ensuremath{\alpha}\ensuremath{-}{\mathrm{ScH}}_{0.27}$ is much weaker than for $\ensuremath{\alpha}\ensuremath{-}{\mathrm{ScD}}_{x}.$ These results indicate that the hopping rate distribution for H atoms in scandium is shifted to much higher frequencies from that for D atoms. The results of our high-resolution quasielastic neutron-scattering measurements on $\ensuremath{\alpha}\ensuremath{-}{\mathrm{ScH}}_{0.27}$ in the temperature range 12--302 K are consistent with this conclusion.