JOURNAL DE PHYSIQUE IV

Abstract. In order to clarify the nature of the numerous thermally activated processes occurring in yttrium, the anelastic relaxation spectrum of polycrystafline samples has been investigated between 1.1 and 600 K in the kHz range, by varying the concentration of interstitial hydrogen and oxygen and in presence of plastic deformation. Besides the main dissipation peak around 300 K due to the formation /dissolution of H pairs and the peak at liquid He temperature attributed to H tunnelling, four processes have been observed. The processes below 300 K can be interpreted by mechanisms involving hydrogen trapped by oxygen, and dislocations dragging interstitial H, whilst the large relaxation observed around 450 K has to be ascribed to oxygen motion in solid solution. 1