Micro-Raman study of the m-MoO2 to alpha-MoO3 transformation induced by cw-laser irradiation

In this work we report the monoclinic-MoO2 to orthorhombic-MoO3 transformation induced by continuous wave-laser irradiation. A Helium-Neon laser was used as energy source. The transformation involved two processes: an initial oxidation followed by a transition from a crystalline phase (MoO2) to the other (MoO3). Both processes, oxidation and structural changes, were monitored in situ by micro-Raman spectroscopy. Structural transformations were analyzed as a function of the laser power and as a function of the exposure time (transformation kinetics). Under these low power irradiation conditions it was found that the monoclinic-MoO2 transforms completely to the well-known orthorhombic phase alpha-MoO3 in a few minutes. (C) 2010 Elsevier B.V. All rights reserved.