Diffusion of hydrogen in HfCr2Hx(Dx) compounds with a C14-type structure: isotope effects

Within a temperature range of 11-404 K in C14-type structure HfCr2Hx (x=0.3 and 0.6) and HfCr2Dx (x=0.28 and 0.64) compounds the velocities of spin-lattice relaxation of 1H and 2D are measured. Electron contributions to the velocity of relaxation and H and D diffusion parameters are estimated from experimental data. H and D atoms in the compounds studied retain their high mobility down to low temperatures. Specifically, typical frequency of H atom jumps in HfCr2H0.3 and HfCr2H0.6 exceeds 2x108 s-1 at T=200 K. A comparison of the data for hydrogenated and deuterated compounds of close compositions shows that at the same temperature the frequency of jumps for D atoms is lower than for H atoms. A normal isotopic effect observed in the frequency of H(D) atom jumps is due to the difference between activation energy of diffusion for two isotopes