NUCLEAR-MAGNETIC-RESONANCE STUDY OF HYDROGEN DIFFUSION IN THE A-15 COMPOUND TI3IR

The spin lattice relaxation time T1(-1) of H in Ti3IrHx was determined from pulsed nuclear magnetic resonance measurements carried out between 5 and 630 K (x = 0.55, 3.0 and 3.5). The results for T1(-1) are quantitatively explained by a superposition of a Korringa relaxation (T1,e(-1)) and a dipolar relaxation (T1,d(-1)) due to H diffusion. The Korringa relaxation times T1,e obey the relation T1,e . T = (87 +/- 4), (124 +/- 8) and (145 +/- 8) sK for x = 0.55, 3.0 and 3.5, respectively. The dipolar relaxation rates T1,d(-1) were analyzed with the help of a modified BPP model, yielding the jump rates of the H in the range between approximately 200 and approximately 500 K. The jump rates depend on the H concentration x. They can be described by an Arrhenius relation with activation energies of (I 55 +/- 15) meV (for x = 0.55), (365 +/- 30) meV (x = 3.0) and (265 +/- 25) meV (x = 3.5). The results for the jump rates are compared with previous measurements of the diffusion coefficient of the H at lower H concentrations (x less-than-or-equal-to 0.02).