Eleventh International Conference on Internal Friction and Ultrasonic Attenuation in Solids
J. Phys. IV France 06 (1996) C8-47-C8-50
Hydrogen-Induced Anelastic Relaxation in Pd-1.9 at % MgOB. Kappesser1, H. Wipf1 and R. Kirchheim2
1 Institut für Festkörperphysik, Technische Hochschule Darmstadt, Hochschulstrasse 6, 64289 Darmstadt, Germany
2 Institut für Metallphysik, Universität Gottingen, Hospitalstrasse 3-7, 37073 Göttingen, Germany
In Pd, MgO precipitates with diameters in the nm range can be produced by internal oxidation of PdMgx samples that are annealed in an O2 atmosphere. The Pd-MgO interfaces can be decorated with excess oxygen, depending on the O2 gas pressure in the final annealing procedure. We studied by mechanical spectroscopy the influence of hydrogen (H) interstitials on the anelastic behavior of internally oxidized Pd-1.9 at%MgO samples (with and without oxygen decoration of the Pd-MgO interfaces, temperature range 4 to 380 K, frequencies between 213 and 685 Hz). The H causes a broad relaxation peak with an activation energy of ~ 0.15 eV for the underlying relaxation process. The peak does not exist in ordinary (pure) Pd doped with H. We conclude that the relaxation peak results from H interstitials that are trapped in the interfacial regions between the MgO precipitates and the Pd. This supports the results of a recent electrochemical study which similarly reports a very effective trapping of H interstitials in these regions. Surprisingly, the relaxation peak was not found to depend on whether the interfacial regions were decorated with oxygen or not.
© EDP Sciences 1996