Fifth European Conference on Internal Friction and Ultrasonic Attenuation in Solids
J. Phys. Colloques 48 (1987) C8-263-C2-268
DOI: 10.1051/jphyscol:1987837
ULTRASONIC INVESTIGATION OF NIOBIUM DEUTERIDES AT LOW TEMPERATURES
F.M. MAZZOLAI1 et H.K. BIRNBAUM21 Physics Department, University of Perugia, I-06100 Perugia, Italy
2 Metallurgy and Mining Engineering Department and Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL 61801, U.S.A.
Abstract
The ultrasonic attenuation measured in NbD0.83 and NbD0.86 deuterides using the C11 mode has been found to show two anelastic relaxation processes at low temperatures (T1 = 156 K, T2 = 250 K for f = 10 MHz). Their activation energies and limit relaxation times are W1 = 0.18 eV, W2 = 0.37 eV t01 = 3x10-14s, t02 = 5x10-16s. Such relaxations show a Curie-Weiss temperature dependence of their relaxation strength and are believed to be due to stress-induced hydrogen density fluctuations occuring within the ß and µ (or ν) forms of the deuteride phase, respectively. Anomalies, which are probably related to the ß-µ and ß-ν phase transitions, are observed both in the elastic constant C11 and in the attenuation. The mobility of D within the different phases as well as the nature of the transitions observed are discussed