A pulsed NMR study of hydrogen diffusion in hydrides of group IVa transition metals

Activation energies Esub(A) for hydrogen diffusion in hydrides of Group IVa transition metals have been determined by 1H nuclear magnetic resonance measurements of spin lattice relaxation in both the laboratory (T1) and rotating (Tsub(1rho)) frames. For the HfHx system both activation energies obtained from T1 data, and the value of T1 at the minimum appear to be insensitive to hydrogen content x in the range 1.58 =< x =< 1.98. For hydrides of titanium and zirconium of approximately stoichiometric composition MH2 (where M = metal), there is excellent agreement between activation energies obtained from T1 and Tsub(1rho) data. Mean activation energies obtained were 0.51 eV for TiHsub(1.98) and 0.83 eV for ZrHsub(1.96), consistent with a single diffusion mechanism in each case over the temperature range 260 to 600 K and 400 to 800 K respectively. In the case of HfHsub(1.98) the agreement was less good, values of 0.64 and 0.55 eV being obtained from T1 and Tsub(1rho) respectively. (author)