NMR evidence of two frequency scales of hydrogen jump motion in Ti2Ni-type compounds Ti2CoHx

Nuclear magnetic resonance measurements of the proton spin–lattice relaxation rate R1 for Ti2Ni-type compounds Ti2CoHx (x=0.56, 0.77 and 1.34) have been performed over the temperature range 20–510 K and the resonance frequency range 13–90 MHz. For Ti2CoH0.77 and Ti2CoH1.34 the temperature dependence of R1 is found to exhibit an additional low-temperature peak near 280 K; the amplitude of this peak increases with increasing H content. These results give evidence for the coexistence of at least two types of hydrogen jump motion with different characteristic frequencies. For Ti2CoH0.56 no additional R1 peak has been found. The concentration dependence of the additional peak is discussed in terms of the occupancy of inequivalent interstitial sites by hydrogen atoms.