STUDIES ON PREPARATION AND PROPERTIES OF THE GAS-SENSING SEMICONDUCTING MATERIAL CD2SB2O6.8

A chemical coprecipitation method is developed to have successfully pr epared the ultramicro powder of Cd2Sb2O6.8 pure phase with a defect py rochlore structure. The effects of the coprecipitation conditions and calcining temperature on the phase compositions and structure are stud ied. The result shows that the pure Cd2Sb2O6.8 phase can be only obtai ned when n(Cd)/n(Sb) molar ratio is kept as around 0.90, while other r atios (i,e, 0.85 and 1.00) lead to impure phases, The minimum calcinin g temperature for the pure phase formation is 750 degrees C, which is lower than that for other methods reported in literature. A formation procedure mechanism of the Cd2Sb2O6.8 phase is proposed in terms of hi gh-temperature ionic diffusion reaction: Cd ions diffuse into a kind o f dehydrated antimony acid which possesses a defect pyrochlore structu re, react and gradually form the ultramicro power of Cd2Sb2O6.8. The g as-sensing properties of the thick film gas-sensor elements made of th is pure Cd2Sb2O6.8 powder are tested. Compared with the elements made of the powders by conventional solid state reaction method, the elemen ts from this wet chemically prepared ultramicro powders show much impr oved gas-sensing properties. The sensitivity to 1.0 x 10(-4) C2H2 is e ven higher than that to 3.0 x 10(-3) H-2 or CO as well as 1.0 x 10(-3) C2H4. The high sensitivity and good selectivity to C2H2 demonstrate i t a promising acetylene gas-sensing material.