A resonant ultrasound spectroscopy study of hydrogen-absorbing intermetallic compounds

Resonant ultrasound spectroscopy has been used to study four different hydrogen-absorbing intermetallic compounds. A fundamental study was undertaken of the properties of hydrogen motion within two different C15 Laves-phase compounds. Also, the hydrogen-absorbing intermetallic compounds, TiCr1.8 and LaNi5, were studied. The polycrystalline elastic moduli were used to calculate various elastic parameters.; Ultrasonic measurements of TaV2H0.18, TaV 2D0.17 and TaV2D0.50 showed a relatively large attenuation peak near room temperature for measurement frequencies of 1 MHz. This peak was associated with the long-range diffusion of H(D). Much smaller attenuation peaks were observed at low temperatures and attributed to local motion. These peaks exhibited a strong isotope effect. The relaxation rate was described by a non-classical expression, with a temperature-dependent mobile population of H(D). The current observation of a low-temperature loss peak for TaV2H0.18 provides convincing details concerning the local motion of hydrogen, including parameters for the extremely fast hydrogen motion and a consistent explanation of the strong isotope effect.; Ultrasonic measurements also showed attenuation peaks in ZrCr2H(D) x with x(H) = 0.09, 0.15 and 0.31 and x(D) = 0.12. These peaks were associated with the diffusive motion of H(D). A large isotope effect was interpreted in terms of quantum mechanisms of diffusion. In the temperature range of our measurements, the dominant mechanism appears to be tunneling transitions between ground states. The current results provide strong evidence for this novel mode of hydrogen diffusion. A small shift was observed in the shear modulus for each material at a temperature corresponding to the relevant peak in the ultrasonic loss.; In a more applied study, the elastic moduli of polycrystalline TiCr 1.8 and LaAlxNi5- x were measured over the range of 3--410 K. The moduli displayed a normal temperature-dependence for simple metals. Debye temperatures and H-H interaction energies were calculated from the measured moduli. The results of this work should prove useful in discerning trends or correlations that could help in the selection of new metal-hydride materials.