X-RAY-DIFFRACTION, TRANSMISSION ELECTRON-MICROSCOPY AND X-RAY PHOTOELECTRON SPECTROSCOPIC CHARACTERIZATION OF IRO2+TA2O5 FILMS

X-Ray diffraction (XRD), transmission electron microscopy (TEM), and X -ray photoelectron spectroscopy (XPS) have been used to characterize I rO2 + Ta2O5 films prepared from chloride solutions heated at 450-750-d egrees-C. Coatings with IrO2 contents greater-than-or-equal-to 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-degrees-C. The rutile phases appear to be ultradisperse IrO 2 crystallites whose boundaries are appreciably modified by Ta2O5: the finer the crystallites the more the contribution of this mixed modifi ed phase. XPS shows that the surface of the films is enriched with tan talum, the contribution of the mixed Ir + Ta oxide phase being display ed 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 ox ide 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 d ispersed into macro- and micro-pores of the gel structure.