The influence of the conditions of the ZrO2 passive film formation on its properties in 1M NaOH

In this paper, results of the potentiodynamic–potentiostatic formation of a homogeneous, passive films of ZrO2 onto a Zr electrode in 1 M NaOH solution at different potentials (2.0, 4.0, 6.0 and 8.0 V vs. SCE) are presented. The properties of such films were investigated by EIS measurements at different potentials. After fitting the EIS spectra by an appropriate equivalent circuit, the capacitance (Cpf) and resistance (Rpf) of these films were determined. All films were found to become insulators at the potentials equal and/or more positive than 2.0 V, with their thicknesses increasing linearly with the potential from about 7 nm at 2.0 V to about 20 nm at 8.0 V. In the potential range 0.8 V < E < 2.0 V a transition from a semiconducting to insulating behaviour has been recorded for all films (except for the one formed at 2.0 V). The donor densities (Nsc) for all films, as well as their flat band potentials (Efb) and their thicknesses of the space charge layer (dsc), were determined from the corresponding Mott–Schottky plots (MS) recorded in the potential range (0.0 V < E < 0.8 V), where all films behaved as n-type semiconductors.