1H nuclear magnetic resonance studies of Hf 2RhH 2.2 and Hf 2CoH 3.8: Structure and diffusion

Abstract

Proton nuclear magnetic resonance relaxation times T 1 T 1 ρ , T 2 and T 1 D are reported for the intermetallic hydrides Hf 2RhH 2.2 and Hf 2CoH 3.8 in the temperature range 77–450 K at 16 and 60 MHz. X-ray diffraction studies showed that the hydrides are cubic ( Fd3m) with lattice parameters a of 12.76 Å and 12.74 Å respectively. A model for the location of the hydrogen atoms is described which is consistent with the observed second moments (16 G 2 and 31 G 2 respectively). Above about 200 K, relaxation is determined by translational diffusion of the hydrogen atoms. The frequency dependence of an empirical spectral density function for hydrogen diffusion was determined from the temperature dependence of T 1, T 1 ρ and T 2 by temperature-frequency superposition. The form of the empirical function and the possible involvement of an IR divergence phenomenon are discussed. Below about 200 K T 1, T 1 ρ and T 1 D become dominated by paramagnetic effects.