Dispersive charge carrier mobility in a surface oxide layer

Abstract

The electrode impedance spectrum of the oxide produced on a Zr–1%Nb surface in an aqueous solution at 290 °C is analysed as a function of temperature between 20 °C and 290 °C. The portion of the spectrum, relevant to the oxide, is treated in terms of a parallel CPE∥R_ox equivalent circuit (CPE denoting constant phase element, R_ox ohmic resistor). Considering also the effect of temperature CPE is understood as a dispersive resistance described by the continuous time random walk theory of Scher and Lax. Distinction is made between the kinetics of oxide growth and of non-Faraday charge transport, the time constant of the latter being obtained directly from impedance data.