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Reactivity of palladium ions implanted into Nb2O5 layers and the Frenkel defects produced

par Patzelt, T.;Schultze, Joachim Walter;Meyer, Otto;Delplancke, Jean-Luc
Référence Surface & coatings technology, 51, 1-3, page (379-384)
Publication Publié, 1992-04

Article révisé par les pairs

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Résumé :

Palladium was implanted into a 55 nm thick anodic oxide film on niobium, which produces Frenkel defects and a loss of oxygen in the total oxide film. Subsequent anodic polarization in 0.5 M H2SO4 leads to complete reoxidation and recrystallization within a growing outer layer, while the shrinking inner part of the implanted film remains reduced and amorphous. Within a thin outer layer, the implanted palladium atoms can be oxidized above and reduced below 0.65 V (vs. a standard hydrogen electrode). This redox potential is about 300 mV less noble than that of the pure palladium metal which proves a higher energetic state of the matrix isolated palladium atoms. X-ray photoelectron spectra show an almost constant concentration of Pd, i.e. Pd2+ ions migrate to form larger palladium clusters. The mobility of protons and water, however, is sufficient for the formation of PdO and reaction. Repassivation of the implanted oxide film causes recrystallization and reoxidation, proved by reflection high energy electron spectroscopy, Rutherford backscattering spectrometry and X-ray photoelectron spectroscopy (RHEED, RBS and XPS). Measurements of the electrode capacity and electron transfer reactions prove the insulating properties of the outer Nb2O5 layer. © 1992