Fabrication and characterization of Fe1.90Ti0.10O3 gas sensitive resistors for carbon monoxide

An iron–titanium solid solution Fe1.90Ti0.10O3 was synthesized by a conventional ceramic route. The powder was incorporated into a gas-sensing device by screen printing a mixture of Fe1.90Ti0.10O3 and vehicle (Agmet ESL-400) onto an alumina tile. Heating the tile to 700 °C removed the organic vehicle and left a porous, stable and uniform layer of Fe1.90Ti0.10O3. This oxide layer showed a reversible n-type change in resistance on exposure to varying concentrations of carbon monoxide, for which the interfering effect of water vapour was small. Titanium was strongly surface segregated, and reduction of Fe(III) to Fe(II) near the surface was found. The behaviour is interpreted with a Mars–van Krevelen model for adsorption and reaction on a complex surface defect. The possibility to control the behaviour through control of the surface segregation is inferred.