ELECTRICAL-TRANSPORT AND IMPEDANCE SPECTRA IN NIO-PD COMPOSITES

The transport properties of the NiO-Pd composites have been investigat ed by ac electrical conductivity measurements at various temperatures between 700-degrees-C and 1200-degrees-C in pure oxygen, air and purif ied argon atmosphere. The electrical conductivity of the composites at first decreases to 2.3 vol% Pd-NiO composition and then increases as a function of the volume fraction of Pd due to the decrease of the pot ential barrier in the space charge regions. The frequency dependance a nd the effects of the second phase in these composites have been chara cterized with impedance spectroscopy. In the complex resistivity plots of the 2.3 vol% Pd-dispersed NiO composite, the low-frequency semicir cle decreases compared to that of undoped, polycrystalline NiO and it is proposed that the potential barrier in the space charge layer gener ated at the interface between Pd second phase and NiO matrix influence s the bulk resistivity.