Semiconductive properties of passive films on amorphous Fe-base alloys

The electronic properties of passive films on amorphous Fe-10Cr-13B-7C and Fe-10Cr-13P-7C alloys and a conventional crystalline stainless steel Fe17Cr were studied by Mott-Schottky analysis and photoelectrochemistry. The passive films on all alloys studied show n-type semiconductive characteristics, but a different behaviour than ideal bulk semiconductors due to their amorphous and defective nature. The passive film on the B-containing amorphous alloy resembles the film on pure iron in its electronic properties, whereas the film on the P-containing alloy is similar to the film on pure chromium. A significant difference can be seen in the amount of defects in the passive films on the different alloys, the presence of which can be seen as localized states in the band-gap. The film on the P-containing amorphous alloy contains much less defects than the films on the B-containing amorphous alloy and the crystalline steel. A comparison with results of earlier electrochemical work shows that the defectiveness of the passive film is connected with the stability of the film