Characterization of thin anodic oxides of Ti–Nb alloys by electrochemical impedance spectroscopy

Abstract

Electrochemical impedance spectroscopy was used to study the interface between the anodic oxide formed on Ti–Nb alloys with specific compositions of Ti–10wt.% Nb and Ti–20wt.% Nb and the electrolyte. The anodic oxides were grown in an acetate buffer of pH 6.0 by using cyclic voltammetry electrochemical technique in which the potential is scanned at a rate of 100mVs−1. The potential applied starts from 0V and increasing at steps of 1V till 8V which allows to study the mechanism and the kinetics involved during the oxide growth. The electrochemical impedance measurements were started prior to applying any potential so that the electronic properties of the native oxide on the Ti–Nb alloys can be determined. The electrochemical measurements were then carried out after each oxide growth so that the electronic properties of the previously grown oxide can also be determined. The variation of the capacitance of the respective oxides determined from the impedance measurements with the applied potential enables the calculation of the relative permittivity of the respective oxides on the two alloys. Moreover the semiconducting properties of the oxides were determined by using Mott–Schottky analysis. The Mott–Schottky analysis involves electrochemical impedance measurements at fixed frequency with increasing applied bias potential so that the variation of the capacitance of the space charge region with the applied potential can be followed. The oxides from both alloys showed an n-type semiconducting property with 7.5×1018cm−3 and 2.4×1019cm−3 donor concentration for Ti–10wt.% Nb and Ti–20wt.% Nb alloys respectively.