The local structure of metal atoms around a H atom, and the dynamics of H atoms in -Ti1-yVyHx disordered metal hydrides, where x was approximately equal to unity and y was between 0.2 and 0.8, was studied by using proton nuclear magnetic resonance techniques. The temperature and frequency dependences of the 1H spin-lattice relaxation time were measured at temperatures ranging from 105 to 400C and frequencies of 9, 22.5, 52 and 90MHz. All of the hydrides exhibited a minimum in the temperature dependence of the spin lattice relaxation time. These were attributed to fluctuations in the 1H-1H and 1H-51V dipolar interactions which were caused by H diffusive motion. The activation parameters for H diffusion were determined by data-fitting, using the Bloembergen-Purcell-Pound theory and taking account of the distribution of correlation times. With increasing V concentration, the apparent activation energy for H diffusion gradually decreased from 24kJ/mol at y = 0.2, to 21.8kJ/mol at y = 0.6. It then rapidly decreased to 17.5kJ/mol at y = 0.8. The local structure of the metal atoms around a H atom was deduced from this composition dependence by using a cluster model which permitted the short-range ordering of metal atoms. The short-range order parameter here was 0.4; a value that was in good agreement with the value of 0.43 that had been estimated from incoherent inelastic neutron scattering data.

T.Ueda, S.Hayashi: Journal of Alloys and Compounds, 1995, 231, 226-32