(Ti, Sn)O2 solid solutions for gas sensing: A systematic approach by different techniques for different calcination temperature and molar composition

Tin-titanium solid solutions at increasing Ti molar fraction, x = 0.1, 0.3, 0.5, 0.7 and 0.9, were prepared by symplectic gel co-precipitation (SGC) method from stoichiometric hydroalcoholic solutions of Ti and Sn metalalkoxides. Structural, spectroscopic and electrical analyses were performed and the results have been correlated. The peaks of the XRD patterns change from the positions of SnO2 cassiterite to those of TiO2 rutile, when increasing the Ti content in the solid solution. Photoluminescence (PL), FT-IR and UV-vis-NIR characterizations are in agreement with the formation of solid solutions: PL peak falls either in the visible or IR region, depending on the Ti content in the solid solution; FT-IR spectra reveal a progressive upward shift of the high-frequency absorption edge of the skeletal vibration modes from the value of SnO2 to one of TiO2 on increasing the Ti content; UV-vis-NIR spectra reveal a progressive downward shift of the VB-CB absorption edge on increasing Ti content. The changes induced by CO interaction at increasing temperature in the FT-IR and UV-vis-NIR spectra revealed a different behaviour of the materials following the Ti content: for the lowest Ti molar fraction (x = 0.1) as well as for SnO2 the reduction gives rise to mono-ionized oxygen vacancies, for the other solid solution the loss of reticular oxygen gives rise to doubly ionized oxygen vacancies and to Ti3+ ions. From the electrical-conductance point of view, two groups of films can be identified: pure SnO2 and the solid solution with x = 0.1, and all the other solutions including pure titania, in agreement with the results of FT-IR investigations. The best response to carbon monoxide was achieved by the solutions with x = 0.3 and x = 0.5. Opposite to electrical properties, exhibiting good responses to reducing gases, these agents did not appreciably modify the PL yield of the solid solutions. Conversely, PL emissions were sensitive to NO2, particularly for Ti0.5Sn0.5O2. © 2009 Elsevier B.V. All rights reserved.