Structure characterization of semiconducting tin and tungsten mixed oxides

Mixed-oxide powders of tin and tungsten were made by heating various mixtur es of SnO and WO3 powders, corresponding to the nominal formula SnxWO3+x wi th x between 0.5 and 2.0, in an argon atmosphere at 600 degrees C for 15 ho urs. The alpha-SnWO4 phase was the result of heating of an equimolar mixtur e of SnO and WO3 powders. In addition to Sn-119 Mossbauer experiments, X-ra y diffraction and Raman spectroscopy were used to study the phase structure s of the mixed-oxide powders. Mossbauer spectra from all samples show a sma ll peak at similar to 0 mm/s from phase(s) like rutile SnO2, and a larger p eak doublet centred at similar to 3.4 mm/s from the alpha-SnWO4 phase, wher e tin is in the form Sn4+ and Sn2+, respectively. Another peak doublet cent red at similar to 3.0 mm/s was needed to obtain reasonable fits for samples with x greater than or equal to 1.3. This doublet originates from an undoc umented phase where tin is also in the divalent form Sn2+. Sn-119 Mossbauer spectroscopy made it possible to reveal the relative amounts of the two va lence states of tin in the mixed-oxide structures. Raman spectroscopy as th e other probe for "local" structures was insensitive to reveal the changes in the phase structures between different mixed-oxide samples up to x = 1.7 2, but an extra peak at similar to 890 cm(-1) in the Raman spectrum from th e sample with x = 2.0 indicates also the presence of the undocumented phase .