Hydrogen Vacancy Diffusion Parameters in ScH2-x and ScD2-x from 45Sc Spin-Lattice Relaxation Time Measurements

Abstract

The temperature dependence of the nuclear spin-lattice relaxation rate R1 of 45Sc has been measured in scandium dihydrides and dideuterides. These data are satisfactorily accounted for by two contributions to R1, R1e due to conduction electrons, and R1Q due to quadrupole interaction fluctuations resulting from vacancy diffusion on the hydrogen (deuterium) sublattice. Describing these fluctuations by a Lorentzian spectral density and Arrhenius behavior for the vacancy hopping, analysis of the data yields values of the Korringa product A = T/R1e and the activation energy Ea and attempt frequency v0 for vacancy-diffusion. In contrast to v0 values based on proton measurements, the 45Sc results agree satisfactorily with the value based on inelastic neutron scattering measurements of hydrogen optic mode vibration frequencies, v0 ≅ 2 x 1014s-1. We conclude that hydrogen-hydrogen interactions are responsible for the lower v0 values derived from proton R1 measurements.