Semiconducting properties of passive films formed on Fe–Cr alloys using capacitiance measurements and cyclic voltammetry techniques

Cyclic voltammetry, capacitance measurements, and AES analysis have been carried out in order to study semiconducting properties of passive films formed on ferritic Fe–Cr alloys in aqueous environments. The influence of Cr content and film formation potentials on their semiconducting properties was investigated in pH 9.2 borated buffer solutions. Cyclic voltammetry results showed that peak current densities of Fe ion species decreased with the increase in Cr content while the reduction peak of Cr6+ to Cr3+ increased. Capacitance measurement results exhibited that passive films characterized n-type and p-type semiconductors, depending upon potentials applied above and below the flat-band potential. Doping densities of passive films decreased with increasing the Cr content and/or the film formation potential. AES results showed that as Cr content and the film formation potential increased, the highest peak of Cr shifted from the outside to the inside of a passive film.