Trapping and Isotope Effects of Deuterium in Nb-5at%Ti

The anelastic relaxation spectrum of the Nb-5 at.% Ti system has been investigated for various deuterium concentrations, cD, between 0.07 and 1.76 at.% in the temperature range 1.2-300K. Three relaxation processes located around 170, 100 and 50K have been observed at a vibration frequency of 20 kHz, and a marked frequency-dependent rise of dissipation is measured below 5K. The maxima increase in height and shift in temperature with increasing deuterium content, but the shifts of the high- and low-temperature peaks are of opposite sign. The peak at the lower temperature grows with the square of c D and becomes the predominant process at higher concentrations. The relaxation processes are attributed to the stress-induced reorientation of titanium-deuterium complexes. These observations are interpreted under the assumption that interaction with Ti substitutionals shifts the energies of the trapping sites occupied by deuterium atoms randomly.