Deuterium motion in yttrium studied by ultrasonic measurements

Ultrasonic-attenuation measurements in YD0.10 reveal broad, asymmetric attenuation peaks that are interpreted in terms of rapid motion of deuterium among interstitial sites in the Y metal lattice. The results are well described with a model involving tunneling among highly asymmetric sites. A weakly temperature-dependent relaxation rate, compatible with coupling of the sites to electrons, accounts for the relaxation up to about 70 K. At higher temperatures a strongly temperature-dependent relaxation rate becomes dominant. The major asymmetries that are responsible for the coupling of the tunneling centers to the ultrasound are attributed to the interaction between D atoms that lie on different c axes.