INVESTIGATION OF HYDROGEN-IMPURITY-COMPLEXES IN TRANSITION-METALS

The relaxation spectra due to the reorientation of diatomic MeH-complexes have been investigated in a large number of alloys of Ni containing small admixtures of other elements Me using the magnetic aftereffect; these alloys, which were preferentially of composition Ni98Me2, have been charged with H and D. Due to the high sensitivity of this technique we were able to investigate complex concentrations even below 100 at-ppm. All impurities Me in Ni investigated formed MeH-(D-) complexes with H(D). The reorientation energies QHD and pre-exponential factors τ0H.D for different impurities have similar values (QH = 0.325 - 0.355 eV, τ0H =1 10-12-5 10-12 s) and show marked isotope effects (QD-QH ≈ 0.045 eV, τ0H/τ0D≈10). From annealing experiments, binding enthalpies, EB, of several MeH-complexes were found to range from 0.05 to 0.12 eV. For MeD-complexes they are approximately 0.02 eV larger. The dependence of the relaxation amplitude on the Me-concentration can be independently used to determine EB and, in the case of NiFe, EB agrees well with the results obtained from the annealing experiments. It is shown that the diffusion and solution properties of hydrogen in diluted alloys should be significantly influenced by the formation of H-complexes. The results of former -permeation experiments on Ni and Ni-4.4% V support these conclusions and can be used to determine the binding enthalpy of VH-complexes. A comparison of the lattice expansion,Δa caused by Me in Ni and the reorientation energies Q of the corresponding MeH- (D-) complexes reveals a clear correlation between Δa and Q. It can be concluded that elastic as well as electronic effects should contribute to the binding energy of MeH(D)-complexes. © by Akademische Verlagsgesellschaft