Influence of the nickel oxide nanoparticles content on the electrical properties of carbon/nickel nanocomposites

Carbon/nickel nanocomposites were prepared using the sol–gel method after the incorporation of nickel oxide (NiO) nanoparticles with different mass ratio between 2 and 10% in organic matrix based on pyrogallol–formaldehyde (PF). The obtained materials (C/Ni) were the subjected of heat treatment under inert atmosphere at 650 °C during 2 h. The X-ray diffraction (XRD) showed the presence of metallic Ni phase in amorphous carbon matrix. The electrical conductivity increases with the concentration of NiO at room temperature and exhibits a percolation phenomenon which is confirmed by transmission electron microscopy (TEM) images. The evolution of the dc conductivity in the temperature range between 80 and 300 K of the C/Ni nanocomposites is explained by the three dimensions variable range hopping transport model (3D-VRH) and the nearest neighbor hopping (NNH). The voltage–current V(I) characteristic presents a negative differential resistance (NDR) at room measurement temperature for a low content of NiO. The NDR phenomen is due to the discontinuity of temperature in the interface atmosphere-sample. The ac conductance shows the dominance of three models depending on the content of NiO: the correlated barrier hopping (CBH), the small polaron hopping (SPH) and the hopping conduction mechanisms.