HYDROGEN-INDUCED ANELASTIC RELAXATION IN PD-1.9AT-PERCENT-MGO

In Pd, MgO precipitates with diameters in the nm range can be produced by internal oxidation of PdMgx samples that are annealed in an O-2 at mosphere. The Pd-MgO interfaces can be decorated with excess oxygen, d epending on the O-2 gas pressure in the final annealing procedure. We studied by mechanical spectroscopy the influence of hydrogen (H) inter stitials on the anelastic behavior of internally oxidized Pd-1.9 at% M gO samples (with and without oxygen decoration of the Pd-MgO interface s, temperature range 4 to 380 K, frequencies between 213 and 685 Hz). The H causes a broad relaxation peak with an activation energy of simi lar to 0.15 eV for the underlying relaxation process. The peak does no t exist in ordinary (pure) Pd doped with H. We conclude that the relax ation peak results from H interstitials that are trapped in the interf acial regions between the MgO precipitates and the Pd. This supports t he results of a recent electrochemical study which similarly reports a very effective trapping of H interstitials in these regions. Surprisi ngly, the relaxation peak was not found to depend on whether the inter facial regions were decorated with oxygen or trot.