An anelastic spectroscopy investigation of carbon nanotubes produced by the high-pressure CO method

H(D)-lattice interactions in single wall carbon nanotubes

“…The main difference is in the annealing temperatures, which are shifted of nearly 50 K for deuterium; typically 500 K for deuterium instead of 450 K. The same variation of the peak height with both the hydrogen and deuterium contents con- firms the unblocking mechanism we proposed for hydrogen [12]. Precisely, the D(H) dynamics would be blocked at high concentrations, as D(H) needs unoccupied neighboring interstitial sites for reorientation.…”

“…1 (full squares), where it is seen that the dissipation monotonically decreases with decreasing temperature. This absence of any relaxation process below 60 K was observed also for the fully hydrogenated samples [12]. In order to test whether thermal treatments introduce a peak, as observed for hydrogen, the present sample D was subjected to subsequent high temperature annealings as specified below, and each one was followed by a measurement down to the liquid helium temperatures.…”

“…This implies a distribution of the relaxation parameters (E a and τ 0 ), which is generally caused by elastic interactions, as it is expected in a highly disordered system like the present one. A quantitative analysis was carried out [12] by the Fuoss-Kirkwood fitting procedure. The best fitting values, after subtraction of the background dissipation by a parabolic law [12], were found to be E a = 54.7 meV, α = 0.26, and τ 0 = 10 -14 s (drawn in Fig.…”

“…In a previous paper [12] the anelastic spectrum of HiPco carbon nanotubes was measured and two relaxation processes, found at 140 and 25 K, have been ascribed to the dynamics of hydrogen in the molecular and atomic form, respectively. That study showed that hydrogen is present in carbon nanotubes even if they are not intentionally hydrogenated and that molecular hydrogen strongly interacts with the hexagonal lattice.…”

“…The peak at 25 K is thermally activated and characterized by a very fast dynamics (10 3 jumps per second at 25 K) [12]. The activation energy obtained by the peak shift with frequency is E a = 54.7 meV, and the pre-exponential factor of the Arrhenius relaxation time is τ 0 = 10 -14 s. The latter value is typical of point defect relaxation and suggests that the process is originated by the dynamics of hydrogen or by H complexes.…”