Eleventh International Conference on Internal Friction and Ultrasonic Attenuation in Solids
J. Phys. IV France 06 (1996) C8-43-C8-46
Diatomic Hydrogen-Metal Complexes in Dilute Palladium-Rare Earth AlloysM. Ege, W. Ulfert and H. Kronmüller
Max-Planck-Institut für Metallforschung, Institut für Physik, Heisenbergstr. 1, 70569 Stuttgart, Germany
The internal friction of hydrogen-doped dilute Pd100-xREx alloys (RE = Gd, Ce) (x = 1 ...9) shows three maxima in the temperature range between 10 K and 300 K. These maxima are interpreted as Zener peak of hydrogen in the β-phase (Ha = 0.11 eV), Snoek-Köster peak (Ha = 0.18 eV) and reorientation peak of diatomic H-RE complexes. The relaxation strength of the latter peak is independent of the RE concentration and depends linearly on the hydrogen content. A value of |λ1-λ2| = 0.036 for the elastic anisotropy of the H-RE complexes is obtained. In alloys with RE = Gd this peak saturates when the hydrogen content is comparable with the RE concentration, whereas in the case of RE = Ce saturation at much lower hydrogen contents is observed. The activation enthalpy Ha of the H-RE reorientation varies with the RE as well as with the H concentration and lies between 0.18 eV and 0.26 eV. The activation enthalpy and the width of the peak increase with increasing RE content. Increasing the H content leads to a decrease of Ha. These features of the reorientation of diatomic H-RE complexes are discussed in terms of a distribution of site enthalpies caused by elastic long-range interaction between a H-RE complex and further RE atoms in its vicinity.
© EDP Sciences 1996