Cathodic electrodeposition of mixed oxide thin films

Cathodic electrodeposition is a rather unexplored route for the synthesis of mixed oxides. Two different mechanisms are generally reported which lead to oxide thin film formation: (i) the direct reduction of the oxidation state of the metallic elèment, (ii) an interfacial pH increase and local supersaturation followed by oxide precipitation. We emphasize the major requirements for mixed thin film formation via electrosynthesis and present results obtained with two different systems of special interest. The first, ZnO/Eu(OH)_x, is based on the second mechanism. The second, TiO₂/WO₃, is a mixed mechanism process. We describe the conditions under which europium oxide can be deposited cathodically. This oxide is obtained by co-deposition with zinc oxide. After a heat treatment at 400 °C, X-ray diffraction shows that the films are mainly made of monoclinic Eu₂O₃. The successful WO₃–TiO₂ mixed film electrodeposition in a wide compositional range is also reported.