MOSSBAUER STUDIES ON TIN-BISMUTH OXIDE CO SELECTIVE GAS SENSOR

Tin-bismuth (Sn-Bi) oxide films prepared by spray-pyrolysis techniques were characterized by in situ conversion electron Mossbauer spectrometry in an atmosphere of CO and CH4. The isomer shift of Sn4+ in Sn-Bi oxide decreased at 250-degrees-C and 400-degrees-C in CO and CH4 atmospheres, respectively. An electrical resistance change was also observed at about 250-degrees-C in CO atmosphere, which showed a selective behavior towards CO gas in comparison to CH4 and C2H5OH gases. These results show that CO gas interacted with bulk as well as with the surface of Sn-Bi oxide at low temperature. The increase in the sensitivity of CH4 and C2H5OH at temperatures around 400-degrees-C at the expense of selectivity towards CO was interpreted in terms of surface as well as bulk interactions, and also the catalytic enhancement by reaction of decomposed products from CH4 and C2H5OH.