Structure Characterization of Semiconducting Tin and Tungsten Mixed Oxides

Abstract

Mixed-oxide powders of tin and tungsten were made by heating various mixtures of SnO and powders, corresponding to the nominal formula WO 3 with x between 0.5 and 2.0, in an argon atmosphere at 600 ¡C Sn x WO 3`x for 15 hours. The phase was the result of heating of an equi-a-SnWO 4 molar mixture of SnO and powders. In addition to 119Sn Mo ssbauer WO 3 experiments, X-ray di †raction and Raman spectroscopy were used to study the phase structures of the mixed-oxide powders. Mo ssbauer spectra from all samples show a small peak at D0 mm/s from phase(s) like rutile SnO 2 , and a larger peak doublet centred at D3.4 mm/s from the phase, a-SnWO 4 where tin is in the form Sn4`and Sn2`, respectively. Another peak doublet centred at D3.0 mm/s was needed to obtain reasonable Ðts for samples with x P 1.3. This doublet originates from an undocumented phase where tin is also in the divalent form Sn2`. 119Sn Mo ssbauer spectroscopy made it possible to reveal the relative amounts of the two valence states of tin in the mixed-oxide structures. Raman spectroscopy as the other probe for ""localÏÏ structures was insensitive to reveal the changes in the phase structures between di †erent mixed-oxide samples up to x \ 1.72, but an extra peak at D890 cm~1 in the Raman spectrum from the sample with x \ 2.0 indicates also the presence of the undocumented phase.

Gas Sensing with Perovskite-like Oxides Having ABO3 and BO3 Structures

“…Then, it behaves as an oxidizing gas decreasing the conductance of an n-type semiconductor like α-SnWO 4 and increasing the conductance of a p-type semiconductor like LaFeO 3 . The results obtained by structural characterization of α-SnWO 4 thin and thick films using x-ray diffraction, Mössbauer spectroscopy, Raman spectroscopy, infrared spectroscopy, optical spectroscopy, Rurherford backscattering spectroscopy, scanning electron microscopy and atomic force microscopy [14,[17][18][19][20][21] support to the reasoning that sensing film surfaces have an important role for the dual conductance response. Changes in polar surface layers of ionic semiconductors and corresponding changes in the electron affinity of the semiconductor may also relate to the dual conductance behaviour [22].…”

“…The α-SnWO 4 thin films were grown by means of reactive co-sputtering from tin and tungsten targets. However, α-SnWO 4 thick films made by screen printing from powders did not show the dual conductance response at exposure to CO and other reducing gases [18,19].…”

Lattice Dynamics of β-SnWO4: Experimental and Ab Initio Calculations

“…20 The present article reports on the description of β-SnWO 4 lattice dynamics structural arrangement that can be considered as reference both for the investigation of its β/α transition and for the transitions and dynamical properties in La 2 Mo 2 O 9 and in β-stabilized LAMOX compounds. The investigations are experimentally based upon accurate polarized Raman scattering measurements at low temperature (extending a former investigation) 21 and infrared (IR) absorption measurements in the high-frequency range. The results are used to probe and establish the accuracy of an ab initio approach to calculate vibrational spectra of such a structure with such elements.…”