1H NMR study of local structure and proton dynamics in β-Ti1−yVyHx

Abstract

The local structure of the metal atoms around a hydrogen atom and the dynamics of hydrogen atoms in disordered metal hydrides β-Ti1−yVyHx (x ∼ 1 and 0.2 ⩽ y ⩽ 0.8) were studied by proton nuclear magnetic resonance (1H NMR). The temperature and frequency dependences of the 1H spin-lattice relaxation time (T1) were measured over the temperature range 105–400 K and at frequencies of 9, 22.5, 52 and 90 MHz. All the hydrides showed a minimum value in the temperature dependence curve of T1, which originated from the fluctuations of 1H1H and 1H51V dipolar interactions caused by the hydrogen diffusive motion in the TiV alloys. The activation parameters for hydrogen diffusion were determined from data fitting using the Bloembergen-Purcell-Pound (BPP) theory taking into account the distribution of the correlation time. With increasing vanadium concentration, the apparent activation energy for hydrogen diffusion gradually decreased from 24 kJ mol−1 for y = 0.2 to 21.8 kJ mol−1 fory = 0.6, and then rapidly decreased to 17.5 kJ mol−1 for y = 0.8. The local structure of the metal atoms around a hydrogen atom was obtained from this composition dependence using a cluster model which allowed the short-range ordering of metal atoms. The short-range order parameter in this work was σ = 0.4 and was in good agreement with that determined from incoherent inelastic neutron scattering (σ = 0.43 ± 0.05).