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Gas-sensing properties of different α-SnWO4-based thick films

Screen-printing technique has been used to fabricate α-SnWO4 thick films on alumina substrates. α-SnWO4 powder was prepared by heating an equimolar mixture of SnO and WO3 powders both in vacuum-sealed silica tubes and in argon atmosphere at 600 °C for about 15 hours. Screenprinted thick films were sintered in air for an hour at different temperatures between 550 °C and 850 °C in order to get different mixed-oxide structures from the partial decomposition of α-SnWO4. X-ray diffraction and EDS (Energy Dipersive Spectroscopy of X rays) have been used for the characterization of the phase structure and composition of the films. The electrical conductivity together with gas-response properties of the films was measured at different temperatures between room temperature and 500 °C. H2S, H2, CO, CH4 and SO2 at different concentrations in synthetic air were used as test gases in the measurements. The powder fused in vacuum had better gas-response properties than that fused in argon atmosphere. The sintering temperature of screen-printed thick films was found to affect their gas-response properties, with an optimum sintering temperature at 550 °C. The α-SnWO4 phase alone in the films showed both high sensitivity and selectivity to low concentrations of H2S at temperatures between 150 °C and 300 °C.