X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopic characterization of IrO2+ Ta2O5 films

Abstract

X-Ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) have been used to characterize IrO₂+ Ta₂O₅ films prepared from chloride solutions heated at 450–750 °C. Coatings with IrO₂ contents 30 mol% contain crystalline IrO₂ and one or two additional rutile phases with very diffuse XRD lines, as well as amorphous Ta₂O₅ which crystallizes above 750 °C. The rutile phases appear to be ultradisperse IrO₂ crystallites whose boundaries are appreciably modified by Ta₂O₅: the finer the crystallites the more the contribution of this mixed modified phase. XPS shows that the surface of the films is enriched with tantalum, the contribution of the mixed Ir + Ta oxide phase being displayed in the XPS peaks by the broadening and the asymmetry change of the core level of the Ir 4f and Ta 4f lines. This morphology of Ir + Ta oxide films is a result of hydrolytic processes in the solutions of the precursors. Ta colloidal and polymeric species (gel) interact with Ir chloride complexes at the surface, while the rest of the solution is dispersed into macro- and micro-pores of the gel structure.