Electrical conduction in composites containing copper core-copper oxide shell nanostructure in silica gel

Composites of nanometre-sized copper core-copper oxide shell with diameters in the range 6.1 to 7.3 nm dispersed in a silica gel were synthesised by a technique comprising reduction followed by oxidation of a suitably chosen precursor gel. The hot pressed gel powders mixed with nanometre-sized copper particles dispersed in silica gel showed electrical resistivities several orders of magnitude lower than that of the precursor gel. Electrical resistivities of the different specimens were measured over the temperature range 30 to 300°C. Activation energies for the coreshell nanostructured composites were found to be a fraction of that of the precursor gel. Such dramatic changes are ascribed to the presence of an interfacial amorphous phase. The resistivity variation as a function of temperature was analysed on the basis of Mott’s small polaron hopping conduction model. The effective dielectric constant of the interfacial phase as extracted from the data analysis was found to be much higher than that of the precursor glass. This has been explained as arising from the generation of very high pressure at the interface due to the oxidation step to which the copper nanoparticles are subjected. Dedicated to Professor C N R Rao on his 70th birthday