The direct observation of anodic Bi 2O 3 formed on bismuth in ammonium dihydrogen phosphate solution

Abstract

Using a relatively thin bismuth layer, sputter-deposited on to an oxide-coated, microscopically flat aluminium substrate, ultramicrotomed sections of anodic Bi 2O 3 have been prepared successfully, allowing direct observation of the film section in the transmission electron microscope. Various important features are observed for the anodic oxide film formed in ammonium dihydrogen phosphate solution. The film is essentially amorphous and consists of two distinct layers of different compositions, comprising an inner, pure oxide layer located adjacent to the metal and an outer layer doped with phosphate anions. The ionic conductivity of the outer, electrolyte-doped layer is considerably lower than the inner, pure oxide layer. Further, the effect of incorporated phosphate anions on the ionic conductivity of the oxide is considerably greater than that reported previously for amorphous anodic oxides on tantalum and niobium.