[en] We present a study of the molecular dynamics in an octylcyanobiphenyl (8CB)-Aerosil complex above the bulk isotropization temperature. Using proton nuclear magnetic relaxation experiments in the laboratory frame (T₁^-1) and in the rotating-frame (T_1ρ^-1), we found a notable increase of the relaxation rates in the kHz frequency range as compared to the bulk 8CB liquid crystal at the same temperature. The field-cycling technique was used for the laboratory frame experiments while a conventional apparatus was used for the rotating frame method. The observed behavior is analyzed with the aid of Monte Carlo simulations on the basis of a two-phase fast-exchange model distinguishing surface-ordered and bulk phases. Two processes affecting the low frequency relaxation could be identified: reorientation mediated by translational displacements, accounting for molecular reorientations, and exchange losses of molecules from the surface to the bulk

[en] Hydrogen diffusion coefficients D in disordered b.c.c. systems V _yTa_1-yH_0.07 (y = 0.25, 0.50 and 0.75) have been measured by means of the pulsed-field-gradient nuclear magnetic resonance over the temperature range 190-435 K. The hydrogen diffusivities are found to depend strongly on the alloy composition, the room-temperature value of D in the sample with y 0.75 being an order of magnitude higher than those in the samples with y 0.25 and 0.50. For all the samples studied, the temperature dependences of H diffusivity follow the Arrhenius law with the activation energies of 0.186 eV (y = 0.25, 306-410 K), 0.182 eV (y = 0.50, 295-401 K) and 0.102 eV (y = 0.75, 190-435 K). These values are in reasonable agreement with those obtained from the proton spin-lattice relaxation measurements reported earlier. The jump lengths of H atoms have been estimated by comparing the measured H diffusivities with the proton spin-lattice relaxation data

[en] The hydrogen diffusivity D in C14-type HfCr₂H_0.4 has been measured by means of the pulsed-field-gradient nuclear magnetic resonance over the temperature range 141-428 K. The temperature dependence of D in this range is found to deviate strongly from the Arrhenius behavior. This is consistent with a quantum nature of H diffusion in HfCr₂H_x. Measurements of the proton spin-spin relaxation rate R₂ in HfCr₂H_x (x = 0.4, 0.6 and 0.74) have revealed the anomalous R₂ peak near 230 K for all the samples studied. The experimental results indicate that this peak originates from slow fluctuations of the proton resonance frequency. Such fluctuations are expected for protons diffusing through a spatially inhomogeneous medium on the length scale of about 500 A. The origin of the inhomogeneity suggested by the R₂ data in HfCr₂H_x remains to be elucidated.

[en] In situ studies of the transition from NaAlH₄ to Na₃AlH₆ are performed by proton NMR for samples doped with TiCl₃ and with Ti₁₃-nanoclusters. The local hydrogen dynamics in the different compounds is studied by the nuclear spin-lattice relaxation. For the Ti-doped NaAlH₄ samples a double-exponential recovery of the nuclear magnetization is observed, indicating two fractions of hydrogen with different mobilities. In Na₃AlH₆ a transition from hindered rotation of the AlH₆ groups to full isotropic reorientation of these groups is observed in the temperature range 200-260 K