Electrical properties of the oxide film formed on nickel during high-temperature oxidation

The electrical properties of the oxide film formed from the high-temperature oxidation of nickel have been evaluated using impedance spectroscopy. The impedance measurements were carried out on already oxidised films at temperatures ranging from 100 to 300°C. The conductivity of the oxide film, σ, was obtained as σ=0.19 exp[−0.39 eV/(kT)] Ω−1 m−1, with an activation energy of 0.39 eV close to that of the NiO published in literatures. The dielectric constant ε was found to be nearly independent of temperature with a value of 0.95, significantly lower than that of the bulk NiO. It was believed that some difficulty in achieving a full contact between the electrode and the oxide film during the measurements might have contributed some error in the measurements of both dielectric constant and electrical conductivity. However, the measured relaxation frequency of fR=2.99×109 exp[−0.43 eV/(kT)] Hz should be accurate because fR is independent of the specimen geometry and electrode/oxide contact area.