Internal Friction Study of Hydrogen and Deuterium Relaxation in Yttrium*

A mechanical-spectroscopy study of the anelastic relaxation of hydrogen pairs in hexagonal YH x single crystals

“…According to the above activation energy, our relaxation peaks exhibit a ∼ 30% broadening against an ideal Debye relaxation [13], thus demonstrating a moderate distribution width of the relaxation rates. A similar broadening was already previously observed for hcp YH x (20 to 30% [10] and ∼ 60% [11]) and for the related system LuH x (30 to 50%) [15].…”

“…Figure 3 compiles our results for energy dissipation Q −1 max at the relaxation peak maxima, plotted vs. H concentration after background subtraction. We point out i) that although the background increased with increasing frequency, the magnitude of the relaxation peaks did not, and ii) that the Q −1 max values obtained in a previous vibrating-reed study [11] on hcp YH x polycrystals fall between the present data for the c-axis and b -axis crystals. Figure 3 shows an essentially linear relationship between Q −1 max and H concentration, which agrees with previous results for hcp YH x [10], [11] and the related system LuH x [15], and only apparently contradicts a Zener relaxation of H pairs if their binding enthalpy is considered [1], [14].…”

“…Within experimental accuracy, the temperatures of the peak maxima depended neither on H concentration nor on crystal orientation. Figure 4 presents an Arrhenius plot of our τ −1 rel together with corresponding data from previous mechanical-spectroscopy [9]- [11], QNS [3], [4] and NMR [5], [6] experiments on hcp YH x . The solid line in fig.…”

“…The QNS experiments yielded ν ≥ 100 • Γ i , which confirms the above suggestion and agrees with a similar conclusion from Gorsky effect [7] and QNS [8] data for hcp LuH x and ScH x . Below 320 K, H diffusion in hcp YH x was studied by mechanical spectroscopy [9]- [11]. The studies were performed on polycrystals, yielding an anelastic relaxation peak, e.g., at ∼ 280 K for a frequency of 500 Hz.…”

“…The studies were performed on polycrystals, yielding an anelastic relaxation peak, e.g., at ∼ 280 K for a frequency of 500 Hz. For symmetry reasons, the peak cannot result from a Snoek relaxation of the H on T (or O) sites [12], so that it was explained either by a stress-induced creation or annihilation of H pairs (Zener relaxation [13]) [1], [9]- [11], [14] or by a stress-induced change of the H distribution between T and O sites [9], [11].…”