X-Ray Diffraction and Scanning Electron Microscopy Studies of Molybdenum Trioxide Prepared by Thermal Oxidation of Elect
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X-RAY DIFFRACTION AND SCANNING ELECTRON MICROSCOPY STUDIES OF MOLYBDENUM TRIOXIDE PREPARED BY THERMAL OXIDATION OF ELECTRODEPOSITED MOLYBDENUM SULFIDE
DANIEL BtLANGER*, GUYLAINE LAPERRIERE* AND MICHEL PREDA** *Ddpartement de Chimie, **Ddpartement de Science de la terre, Universitd du Quebec A Montrdal, C.P. 8888, succursale "A", Montrdal (Qudbec), Canada, H3C 3P8.
ABSTRACT Scanning electron microscopy and X-ray diffraction have been used to characterize the transformation of electrodeposited molybdenum trisulfide thin film and powder to molybdenum trioxide. Scanning electron microscopy shows that the formation of molybdenum trioxide is accompanied by an enhancement of the surface area of the film as the relatively smooth molybdenum trisulfide is converted to molybdenum trioxide displaying a platelet structure. X-Ray diffraction revealed that amorphous molybdenum sulfide is converted to polycrystalline molybdenum oxide upon heating in air above 4000C. The observed diffraction peaks obtained when molybdenum sulfide was heated at 4000C for 15 min. correspond fairly well with those of orthorhombic molybdenum trioxide. However, when the molybdenum sulfide powder was heated at 4000C for a period of only about 2 min., additional diffraction peaks were observed. The latter can be attributed to monoclinic molybdenum dioxide. INTRODUCTION Transition metal oxide like molybdenum trioxide has been extensively studied in the past decade because it can be used as positive electrode in rechargeable lithium batteries [1], as active and selective catalyst for the partial oxidation of hydrocarbons and alcohols [2] and in electrochromic devices [3-7]. Molybdenum trioxide thin films have been prepared by electrodeposition processes [4-6]. Recently, we [7] and others [8] independently disclosed a similar technique based on the thermal oxidation of molybdenum sulfide thin films. Thus, Morrison and coworkers [8] have shown that highly oriented molybdenum trioxide thin films were prepared by oxidizing, in pure oxygen atmosphere, oriented films of molybdenum disulfide. In our case, we have demonstrated that an electrochromic molybdenum trioxide thin film was obtained when a molybdenum trisulfide thin film electrodeposited onto a tin oxide-coated glass substrate was heated in air [7]. The transformation of molybdenum trisulfide into molybdenum trioxide has recently been investigated by thermogravimetric analysis [9]. The thermogravimetric data revealed an initial weight decrease that can be attributed to a rapid loss of sulfur upon heating a molybdenum trisulfide thin film in air. Following further heating a minimum weight was noticed and followed by an increase of the weight. This suggests that the formation of molybdenum dioxide occurs prior to that of molybdenum trioxide. One of the objectives of this work is to determine the mechanism for the formation of molybdenum trioxide upon heating molybdenum trisulfide in air. Another objective is to detect the presence of molybdenum dioxide in the heated material by X-ray diffraction. This pape
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