STRUCTURAL AND ANALYTICAL CHARACTERIZATION OF AN IRIDIUM OXIDE THIN-LAYER

Iridium oxide thin layers were studied by comparison with iridium dioxide. Analyses of commercial IrO2 showed the compound to be either an iridium oxychloride (Ir0.14IIIIr0.86IVO10.86Cl0.14) with an X-ray diffraction diagram in disagreement with the reported rutile structure of the phase, or a mixture of pure IrO2 with another oxychloride phase. Chlorine-free preparations of IrO2 showed a perfect rutile type, as proved by single crystal structure determination and powder X-ray parameters refinements (a = b = 4.4983(1) angstrom and c = 3.1547(1) angstrom). As expected, chlorine was found also in the iridium dioxide thin layers obtained by sputtering and in the commercial elemental iridium powder. Thermal gravimetric analyses performed on crumbs of the layers suggested a formula close to IrO1.86Cl0.14, 2.6H2O, assuming a simple oxygen-chlorine substitution. X-ray absorption and diffraction studies showed that, according to the lack of medium range order in the thin layer, the local order of they oxygen octahedra around iridium atoms is modified as compared to the bulk material. However, the thin layers are actually amorphous from the X-ray diffraction point of view.