The influence of hydrogen and dislocations on the internal friction in yttrium

Dynamics of hydrogen, oxygen, and dislocations in yttrium by acoustic spectroscopy

“…25 The following considerations suggest that P5 is caused by a mechanism involving dislocations and interstitial hydrogen: ͑i͒ The process is more developed in sample Y0 where the dislocation density and the H concentration are higher than in Y1; ͑ii͒ the relaxation curve, about twice broader than a single Debye peak ͑Table I͒, is not compatible with pointdefect relaxation; ͑iii͒ a relaxation, with similar features, has been observed in plastically deformed polycrystalline Y. 8 The mechanism of peak P5 should be similar to those reported in transition metals ͑Nb, Ta, V͒ and attributed to the relaxation of dislocations dragging interstitial solute impurities, 26,27 which in the present case are the H interstitial atoms. According to this picture, the observed decrease of P5 after annealing can be explained by the concomitant reduction of the dislocation density and H concentration.…”

“…It is now accepted that P2 is due to H tunneling 7,14 and P6 to the formation or dissolution of H pairs; [6][7][8][9][10][11] instead, the nature of the other peaks has not been convincingly clarified yet. Our investigation confirms the relaxation parameters of P6 reported in the literature, 1,6,11 and this process will not be discussed further.…”

“…That process is attributed to a Zener-type mechanism of stress-induced ordering of the H pairs. 6,11 High-sensitivity acoustic spectroscopy measurements in yttrium have revealed an unexpectedly rich relaxation spectrum, 7 even in samples which are generally considered pure in the literature. The nature of these processes has not been clarified yet, but their appearance denotes that in yttrium several types of imperfections, other than hydrogen, play a role which cannot be ignored for a full understanding of the physical properties of this element and its alloys.…”

“…The interest is both of technological and fundamental nature: These metals can absorb massive quantities of hydrogen 1 ͑e.g., up to xϭ3 in YH x ͒ with promising perspectives for hydrogen storage; their hydrides exhibit metalinsulator transitions accompanied by drastic changes in the optical properties; 2 the high mobility of hydrogen in the hcp lattice allows the observation at low temperature of effects associated with the hopping [3][4][5][6][7][8][9][10][11] and tunneling motion of the H atom. 7,[12][13][14][15] On the other hand, a thorough characterization of these metals at low impurity content is still lacking 16 because of their strong affinity with O and H; the samples are easily contaminated during high-temperature treatments, but it is difficult to determine the exact contents of O and H. A common method of determining the total amount of impurities in metals is the evaluation of the residual resistivity at 0 K, which is due to the electron scattering by foreign atoms.…”