hide
Free keywords:
Hydrogen diffusivity; Yttrium dihydrides; Pulsed-field-gradient nuclear magnetic resonance
Abstract:
The hydrogen diffusivities D in yttrium dihydrides YHx have been measured by means of pulsed-field-gradient nuclear magnetic resonance (PFG-NMR) up to 920 K for x=1.91 and up to 620 K for x=1.95 and 2.03. The observed D values are generally significantly greater than those in the dihydrides of titanium and zirconium. The activation enthalpy Ha, obtained by fitting an Arrhenius expression to the diffusivities, decreases substantially with increasing x from Ha=0.53 eV (x=1.91) to Ha=0.38 eV (x=2.03). Measurements of the proton spin-lattice relaxation Γ1 have been performed on the same samples. The temperature and concentration dependences of the dipolar relaxation Γ1d are consistent with the PFG results. Besides Γ1d and the electronic relaxation Γ1e, the Γ1 data reveal contributions due to very small concentrations of paramagnetic impurities Γ1p, which dominate the measured rates below about 500 K, even at impurity levels as low as 20 ppm or less.
