A detailed study of the relaxation processes occurring below room temperature has been carried out by charging polycrystalline Sc with different amount of hydrogen and deuterium. For all the concentrations, we have observed relaxation effects ascribed to tunnelling of H (D) between the two equivalent first neighbour tetrahedral sites in the c direction, which strongly depend on the H (D) content. In diluted Sc-H (up to few hundreds ppm H), due to the presence of interstitial O, the main anelastic peak is related to the tunnelling of H trapped by O. Increasing the H (D) concentration the traps are saturated and new peaks appear at lower temperature. A marked isotope effect is observed; the peaks shift in temperature and are at least four times smaller with H than with D, when measured at the same frequency. In deuterated sample the main peak has been analysed in terms of the two-level-systems (TLS). A good fit for the case of 1 at.% D could be obtained with a relaxation time tau alpha T-7 and a small distribution of the asymmetries. This indicates that, quite surprisingly, the rate in this temperature range is dominated by multiple phonons processes. (C) 2003 Elsevier B.V. All rights reserved.
Hydrogen and deuterium tunnelling in scandium / Trequattrini, Francesco; F., Cordero; G. C., Cannelli; Cantelli, Rosario. - In: MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING. - ISSN 0921-5093. - STAMPA. - 370:1-2(2004), pp. 118-122. (Intervento presentato al convegno 13th International Conference on Internal Friction and Ultrasonic Attentuation in Solids tenutosi a Bilbao, SPAIN nel JUL 08-12, 2002) [10.1016/j.msea.2003.08.094].
Hydrogen and deuterium tunnelling in scandium
TREQUATTRINI, Francesco;CANTELLI, Rosario
2004
Abstract
A detailed study of the relaxation processes occurring below room temperature has been carried out by charging polycrystalline Sc with different amount of hydrogen and deuterium. For all the concentrations, we have observed relaxation effects ascribed to tunnelling of H (D) between the two equivalent first neighbour tetrahedral sites in the c direction, which strongly depend on the H (D) content. In diluted Sc-H (up to few hundreds ppm H), due to the presence of interstitial O, the main anelastic peak is related to the tunnelling of H trapped by O. Increasing the H (D) concentration the traps are saturated and new peaks appear at lower temperature. A marked isotope effect is observed; the peaks shift in temperature and are at least four times smaller with H than with D, when measured at the same frequency. In deuterated sample the main peak has been analysed in terms of the two-level-systems (TLS). A good fit for the case of 1 at.% D could be obtained with a relaxation time tau alpha T-7 and a small distribution of the asymmetries. This indicates that, quite surprisingly, the rate in this temperature range is dominated by multiple phonons processes. (C) 2003 Elsevier B.V. All rights reserved.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
