NMR studies of diffusion in the metallic glassTiCuHx

Proton relaxation times have been measured in the glassy hydride $a-\mathrm{TiCu}{\mathrm{H}}_x$ for $1.27<~x<~1.35$ over the temperature range 100 to 430 K. Analyses of the proton $T_2$ and $T_{1D}$ relaxation times indicate that hydrogen mobility in amorphous TiCu${\mathrm{H}}_{1.3}$ is significantly greater than in crystalline TiCu${\mathrm{H}}_{0.94}$ or fcc $\gamma -\mathrm{Ti}{\mathrm{H}}_x$. Furthermore, $a-\mathrm{TiCu}{\mathrm{H}}_x$ exhibits non-Arrhenius behavior with four different diffusion activation energies being obtained, whereas diffusion in both TiCu${\mathrm{H}}_{0.94}$ and $\gamma -\mathrm{Ti}{\mathrm{H}}_x$ can be represented by single activation energies over wide temperature ranges. These results demonstrate that local structure plays a major role in the diffusion mechanisms in both the crystalline and amorphous hydride phases. A partial, but irreversible, decomposition of the $a-\mathrm{TiCu}{\mathrm{H}}_x$ phase was also observed near 420 K.