Sites and dynamics of hydrogen in TI0.1V0.9HxDy (x+y approximate to 0.7) as studied by H-1 nuclear magnetic resonance

Ti0.1V0.9HxDy (x + y approximate to 0.7) alloys have been studied by means of X-ray powder diffraction, differential scanning calorimetry (DSC) and H- 1 nuclear magnetic resonance (NMR). The crystal structures of the H-rich sa mples and the samples of [H]/[D]=1 are body-centered-tetragonal (bct) at ro om temperature, while those of the D-rich samples are body-centered-cubic ( bcc). A phase transition similar to that from the delta(D) phase to the alp ha(D) phase is observed around 200-220 K in all the samples except for the hydride. In the hydride, Ii atoms occupy the octahedral (O) sites. In the I I-rich samples, H atoms occupy both the O and tetrahedral (T) sites. In the sample of [H]/[D]=1 and the D-rich sample, H atoms occupy the T sites. The temperature and frequency dependence of H-1 spin-lattice relaxation times (T-1) has been analyzed by modified Bloembergen-Purcell-Pound (BPP) equatio ns. The activation energy of Ii diffusion is higher in the O sites than in the T sites. D addition to the hydride and Ti addition decrease the activat ion energy in the O sites. The H diffusion in the T sites is not affected b y the Ti addition or by the [H]/[D] ratio. (C) 2000 Elsevier Science S.A. A ll rights reserved.