Influence of Thermal Annealings in Argon on the Structural and Thermochromic Properties of MoO3 Thin Films

The effect of thermal annealing in an inert atmosphere (argon) on the structural and thermochromic properties of MoO3 thin films was investigated. MoO3 thin films were deposited by thermal evaporation in vacuum of MoO3 powders. X-ray diffraction patterns of the films showed the presence of the monoclinic Magneli phase Mo9O26 for annealing temperatures above 250?C . Absorbance spectra of the films annealed in argon indicated that their thermochromic response increases with the annealing temperature in the analyzed range (23 ?C ?300 ?C ), a result opposite to the case of thermal annealings in air, for which case the thermochromic response shows a maximum value around 200 ? C?225 ? C and decreases for higher temperatures. These results are explained in terms of a higher density of oxygen vacancies formed upon thermal treatments in inert atmospheres.