Diffusion of hydrogen isotopes in the cubic Laves phase A1₂Gd

Abstract

In the cubic (C15) Laves phase AI₂Gd the diffusion of hydrogen and deuterium was investigated using the method of the magnetic after-effect. The samples were charged electrolytically; the hydrogen concentration obtained was determined by means of thermal desorption measurements and was shown to be at most only 0–01 hydrogen or deuterium atoms per formula unit. The after-effect spectra showed peaks at 58 and 69 K after hydrogen charging and peaks at 70 and 85 K after deuterium charging. Numerical analysis of the spectra yielded short-range diffusion activation enthalpies of 0·13 ± 0·01 and 0·16 ± 0·01 eV for hydrogen and 0·15 ± 0·01 and 0·18 ± 0·01 eV for deuterium, with pre-exponential factors of T₀ = 0·5 × 10–11±0·5 S(hydrogen) and T₀ = 3 × 10–11±0·5 S(deuterium). From these data, conclusions can be drawn concerning diffusion paths and occupation of interstitial sites by hydrogen and deuterium atoms in AI₂Gd. By quantum-mechanical evaluation the lattice activation energy and the parameters of the potential well can be determined.