Abstract: A chemical coprecipitation method is developed to have successfully prepared the ultramicro powder of Cd₂Sb₂O_6.8 pure phase with a defect pyrochlore structure. The effects of the coprecipitation conditions and calcining temperature on the phase compositions and structure are studied. The result shows that the pure Cd₂Sb₂O_6.8 phase can be only obtained when n (Cd)/ n (Sb) molar ratio is kept as around 0.90, while other ratios (i.e. 0.85 and 1.00) lead to impure phases. The minimum calcining temperature for the pure phase formation is 750 ℃, which is lower than that for other methods reported in literature. Aformation procedure mechanism of the Cd₂Sb₂O_6.8 phase is proposed in terms of high temperature ionic diffusion reaction: Cd ions diffuse into a kind of dehydrated antimony acid which possesses a defect pyrochlore structure, react and gradually form the ultramicro power of Cd₂Sb₂O_6.8 . The gas sensing properties of the thick film gas-sensor elements made of this pure Cd₂Sb₂O_6.8 powder are tested. Compared with the elements made of the powders by conventional solid state reaction method, the elements from this wet chemically prepared ultramicro powders show much improved gas sensing properties. The sensitivity to 1.0×10^-4 C₂H₂ is even higher than that to 3.0×10^-3 H₂ or CO as well as 1.0×10^-3 C₂H₄. The high sensitivity and good selectivity to C₂H₂ demonstrate it a promising acetylene gas sensing material .

Key words: Chemical coprecipitation method, Defeat pyrochlore structure, Cd₂Sb₂O_6.8, Formation procedure mechanism, Acetylene gas-sensing property