Low-temperature H-1 nuclear magnetic resonance study of crystal and electronic structures of the nearly stoichiometric yttrium dihydride

Proton nuclear magnetic resonance absorption spectra and spin-lattice relax ation rates in yttrium dihydride have been measured in the temperature rang e from 4.2 to 310 K at 36.0 MHz. The second moment of the resonance line co rresponds to the rigid-lattice regime for YH1.99 and its value agrees with the anticipated CaF2 type of structure. The main contribution to the spin-l attice relaxation rate R-1 arises from conduction electrons and is characte rized by R-1e = 2.77 x 10(-3) s(-1) K-1 x T. Evidence of proton self-diffus ion was seen in the linewidth and in R-1 for YH1.99+0.1 The onset temperatu re, about 250 K, of the self-diffusion, is close to the metal-semiconductor transition reported earlier for that hydride. Below that temperature the l inewidth becomes temperature independent and the second moment of the line is explained in terms of different structure models. The fit to the tempera ture dependence of R-1 in the temperature range 70-310 K gives R-1e = 2.1 x 10(-3) s(-1) K-1 x T. The relaxation becomes almost temperature independen t below 50 K. Various mechanisms for this behaviour are discussed. In addit ion, the R-1 data for the sample prepared with yttrium of 99.9% purity are presented. In contrast with the previous case, where pure yttrium from the Ames Laboratory was used, R-1 has a large contribution of spin diffusion to the paramagnetic Gd3+ ions.