NMR analysis of nuclear relaxation mechanisms in Pd–H and Pd–Ag–H alloys

Crystalline Pd 1-x Ag x -H y (x = 0-0.35) alloys were studied as model systems representing a chemically disordered system for hydrogen-storage materials. Extensive 1 H relaxation rate (R 1 , R 1p and R 2 ) measurements were carried out in a wide temperature range of 2.4-400 K. Palladium-silver alloys of silver concentration as high as 35 at.% were studied by NMR spectroscopy for the first time. The relaxation mechanisms magnetic dipolar relaxation (hydrogen diffusion), Korringa relaxation, relaxation by paramagnetic impurity ions and cross-relaxation to quadrupolar metal nuclei were identified and characterized. The presence of cross-relaxation between 1 H and quadrupolar 105 Pd nuclear spins was assumed and demonstrated for the first time in Pd-H and Pd 1-x Ag x -H systems. More than one jump processes of diffusing hydrogen were found to be present in the studied palladium-silver alloys. Only lower estimated limit values of Korringa constants could be obtained since no frequency independent R 1 versus T region was found. These values are significantly higher than the ones reported by others.