Determination of the hydrogen diffusion mechanism in γ -titanium hydride using nuclear magnetic resonance

In the γ phase of TiHₓ, hydrogen atoms are known to occupy the tetrahedral interstitial sites which form a simple cubic sublattice in the fcc titanium host. To determine to which nearest-neighbor site diffusing H atoms jump during their migration through the lattice, NMR measurements of (i) the hydrogen diffusion coefficient D, between 450 and 550^∘{}C and (ii) the proton-spin-system longitudinal relaxation time, T₁, between 80 and 550^∘{}C are presented for TiH1.55 and TiH1.71. From the relationship D=fTL²(6τd), the jump length L is determined from the measured D values and values of the mean residence time between atomic hops τd, calculated from T₁ data. The tracer correlation factor fT is obtained from the literature. The diffusion and T₁ relaxation data are shown to be consistent with a first-nearest-neighbor hopping model.