Resonant ultrasound spectroscopy has been used for the measurement of the elastic moduli of a Ti-based quasicrystal, one of the major classes of quasicrystals. Both the bulk and shear elastic moduli of a Ti-Zr-Ni multigrained icosahedral quasicrystal and a polycrystalline 1/1 approximant were measured over the temperature range of 15-300 K. The elastic moduli of these two materials are very nearly the same, a result in agreement with the belief that the structures of these two materials are closely related. The temperature dependence of the moduli resembles that of ordinary metals. The results have been used to predict the acoustic contribution to the low-temperature specific heat. This contribution is much larger in these Ti-based materials than for the Al-based quasicrystals reported by others. Besides their general interest, the elastic moduli are useful for constructing atomic potentials in these unusual materials. ͓S0163-1829͑99͒09517-X͔

Ultrasonic attenuation measurements have been performed on the Ti-Zr-Ni alloy system over the temperature range 35-335 K. Both a multigrained icosahedral quasicrystal and a 1/1 bcc polycrystalline approximant were studied. The alloys were hydrogenated to a hydrogen to metal ratio of 0.79 for the icosahedral phase and 0.20 for the crystalline phase. Temperature-dependent attenuation peaks were observed in the alloys loaded with hydrogen while the hydrogen-free materials showed no unusual features. For measurement frequencies near 1 MHz the attenuation maxima occurred near a temperature of 250 K for the crystalline phase and 220 K for the icosahedral phase. The results imply that the hydrogen motion is about one order of magnitude faster in the icosahedral phase than in the approximant phase. Whether this result is due to an intrinsic difference between the two Ti-Zr-Ni phases or to a dependence on hydrogen concentration cannot be determined from the present measurements.