Synthesis of nanocrystalline nickel oxide by controlled oxidation of nickel nanoparticles and their humidity sensing properties

Nickel-silica nanocomposites were prepared by the sol-gel route. By subjecting these to an oxidation treatment in the temperature range 723-1023 K, nickel oxide films of estimated thicknesses in the range 0.5-1.5 nm were grown on the nickel nanoparticles. dc electrical resistivity was measured in the temperature range 300-570 K. The data indicate that an amorphous phase in the interfacial region of the oxide-coated nickel nanoparticles determines the electrical conduction. A small polaron hopping conduction is found to be operative. The humidity sensing properties of these nanocomposites were measured at 300 K in the range of relative humidity (RH) from 3% to 87%. Electrical conductance in all specimens showed an increase of about three orders of magnitude as the RH was raised. Specimens subjected to higher oxidation treatment showed a higher conductance for a specific value of RH. This is ascribed to the presence of a larger number of Ni³⁺ ions in such specimens.