Complex admittance of surface oxide on metastable niobium super-fine particles

Temperature dependence of complex admittance and growth process of surface oxide were investigated. New dispersion relations of dielectric constant and conductance were found in the inital state of the oxidation of niobium super-fine particles. The frequency dependence of dielectric constant (∝ capacitance) showed a resonant type characteristics with a very low resonant frequency ω 0 ∼1 kHz σ ( ω ) steeply decreased above the resonant frequency. These characteristics strongly depended on the product of oxygen pressure and time. These new dispersion relations suggest the existence of any kind of ordered structure on the surface before a thick insulator is formed. In the initial stage of oxidation, a phase transition was found at 158 K. The temperature dependences of capacitance and conductance below 158 K suggest the growth of metallic region in the surface oxide.