An ultrasonic study of hydrogen (deuterium) motion in the C-15 Laves phasecompound TaV2H(D)(x)

Ultrasonic measurements have been carried out on TaV2H(D)(x) over the tempe rature range of 15-335 K. Temperature-dependent attenuation peaks were obse rved with maxima near 250 K for measurement frequencies near 1 MHz. These p eaks are believed to be due to the same process as responsible for maxima i n NMR spin-lattice relaxation rates observed at higher frequencies and temp eratures, and associated with long-range hydrogen diffusion. The present re sults for activation energies and attempt frequencies are in agreement with the NMR results in the temperature range of the spin-lattice relaxation ra te measurements, but the ultrasonic data suggest the presence of two Arrhen ius processes for the long-range motion below about 200 K. The most signifi cant result of the present measurements concerns a possible second peak at low temperatures associated with the local motion found in NMR and neutron measurements. For the present results, such a peak was not found in TaV2Hx, but there was an indication of such a peak in TaV2Dx for temperatures belo w 50 K. These results suggest that the H hopping rate for the local motion in TaV2H(D)(x) remains well above the ultrasonic frequencies used throughou t the temperature range of the measurements, but that the D hopping rate is somewhat lower.