Eleventh International Conference on Internal Friction and Ultrasonic Attenuation in Solids
J. Phys. IV France 06 (1996) C8-73-C8-76
Diffusion of Hydrogen and Deuterium in Titanium Hydride and DeuterideB. Kappesser and H. Wipf
Institut für Festkörperphysik, Technische Hochschule Darmstadt, Hochschulstrasse 6, 64289 Darmstadt, Germany
In the hydrogen (H) concentration range 1.6≤x≤1.8, TiHx exists in a δ phase where Ti forms a fcc lattice in which the H occupies tetrahedral interstitial sites. We studied the diffusion of the H in this phase by mechanical spectroscopy (temperatures from 5 to 370 K, vibrating reed technique, frequencies from 169 to 1 290 Hz). We find a large H-induced Zener-relaxation peak between 240 and 270 K (for the present frequencies) from which we determined the jump rate of the H interstitials with the help of a recent theoretical model for the Zener relaxation. The jump rate follows an Arrhenius relation with an activation enthalpy of (0.49 ± 0.04) eV. An extrapolation of the present results agrees well with previous high-temperature data from neutron spectroscopy and nuclear magnetic resonance. For concentrations x > 1.8, a continuous (ferroelastic) phase transition takes place below ~ 320 K, changing the fcc Ti lattice into fct (ε phase). The phase transition is accompanied by a drastic softening of Young's modulus which allows a very precise determination of the transition temperature.
© EDP Sciences 1996