Synthesis and gas sensing properties of nanostructured CoSb2O6 microspheres

Nanostructured CoSb2O6 microspheres were prepared by a colloidal method using cobalt nitrate, antimony trichloride and n-dodecylamine in ethyl alcohol. Microwave radiation, with a power of ∼160 W, was applied for solvent evaporation. The full evaporation was reached after a non-continuous radiation for 200 s. The resulting material was then heated at 200 °C in static air. At this temperature, a large number of microspheres with smooth surface were formed. The calcination at 700 °C produced single-phase nanostructured CoSb2O6 hollow microspheres. The surface nanoparticles had an average particle size of 38 nm. The gas sensing properties of CoSb2O6 thick films were investigated at 400 °C. The direct current measurements showed resistance variations (ΔR) of ∼130 Ω in CO2 and ∼75 Ω in O2. In a previous work, these values were 450 and 180 Ω, respectively, corresponding to CoSb2O6 synthesized by a solution-polymerization method. Even though a decrease in ΔR was recorded in the present study, more stable measurements in carbon dioxide were obtained, with lower resistance values. The polarization curves showed a large non-ohmic behavior, with a significant ability to detect variations in the concentration of CO2 and O2. Alternating current was also used to characterize the gas sensing properties of CoSb2O6. The measurements in AC revealed better repeatability in gas detection and also the capability to detect variations in the gas concentration.