Nuclear-magnetic-resonance studies of hydrogen antitrapping effects by impurities (Mn,Cr,Fe) in zirconium dihydride

We report nuclear-magnetic-resonance measurements of the proton spin-lattice relaxation time T1 in both pure and paramagnetic impurity-containing zirconium dihydrides. Measurements of the temperature dependence of the proton spin-lattice relaxation times T1 were made on two series of ZrHx samples (pure and impurity doped). The results show that paramagnetic impurities (Mn,Cr,Fe) contribute an additional spin-lattice relaxation rate R1p, which is observed to increase in the sequence Fe→Cr→Mn and also to increase sharply with increasing hydrogen concentration at fixed impurity content in each case. The former result is consistent with the experimental results that the tendency towards localized moment formation in zirconium increases in the same sequence, whereas the latter may be accounted for by the antitrapping character of these impurities. Furthermore, the fit of R1p data for the ZrH1.97 sample doped with 500 ppm Mn or Cr yields an activation energy Ea=0.78 eV/atom, which is ∼75% of Ea in the bulk