X-RAY PHOTOELECTRON-SPECTROSCOPY STUDIES OF FIRED PALLADIUM ELECTRODE INK MATERIALS

The oxidation state of palladium in an electrode ink dispersion, air-dried on barium titanate dielectric substrates, has been studied using x-ray photoelectron spectroscopy (XPS) as a function of both firing temperature and firing atmosphere. Several different states have been identified in amounts which vary over the firing temperature range of interest, i.e. palladium metal, a so-called PdO(ads) species, PdO and palladium in one or more higher oxidation states. No significant differences were observed for the two different contacting atmospheres used during firing, namely air and flowing nitrogen. Owing to overlap of the Pd 3p3/2 and the O 1s spectral envelopes, peak fitting of the oxygen signal was not attempted. Small amounts of residual carbonaceous ash were detected for all the samples studied over the whole range of firing temperatures employed. XPS analysis of a sample of the palladium ink, fired to 1350-degrees-C in air and subsequently etched using a fast atom bombardment (FAB) argon source, showed that the sub-surface palladium was metallic in nature although the original metal surface was composed almost entirely of PdO. Thus, for these palladium inks, when fired to temperatures comparable with those used in multilayer ceramic capacitor (MLCC) manufacture, apart from a thin surface oxide layer the palladium present is in the metallic form, as required for electrode layer conduction.