Electrochemichromism of Nb[sub 2]O[sub 5] Thin Films Obtained by Oxidation of Magnetron-Sputtered NbN[sub x]

Amorphous Nb{sub 2}O{sub 5} thin films are obtained from the thermal oxidation in air at 300{degrees}C of magnetron-sputtered NbN{sub {ital x}} on transparent electrodes. Their optical transmittance is of the order of 80% in the visible wavelength range, and their optical gap is 3.9 eV. Quality of oxide films is directed by the density of the initial NbN{sub {ital x}} film. Electrochemichromic (ECC) behavior of these films is studied in aqueous H{sub 2}SO{sub 4} solution. Reversible optical changes are observed between {minus} 0.8 and 0.2 V {ital vs}. saturated calomel electrode. Optical densities over unity are obtained at lower voltage. Voltammetric, chronoamperometric, and ac impedance measurements have been performed in order to understand better the mechanism of this process. Experimental results are discussed in the frame of a theoretical model for the insertion of species in thin plane metallic films.