Evidence of improvement in gas sensing properties of nanostructured bismuth cobaltite prepared by solution-polymerization method

Polycrystalline powders of bismuth cobaltite, Bi10Co16O38, with sillenite-type structure were prepared by solid-state reaction, solution and solution-polymerization methods, followed by calcination at 600 °C. By the solution-polymerization route, an aqueous solution containing metal nitrates, poly(vinyl alcohol) and sucrose was used to create a polymeric chain with the cations homogeneously distributed. After calcination, from X-ray powder diffraction patterns, an orthorhombic structure with space group Pmmm and cell parameters a = 7.2074 Å, b = 7.1497 Å and c = 5.0912 Å were calculated. The morphological observation of the samples by electron microscopy showed that the powders prepared by the solid-state reaction and solution processes had micron-sized grains, whereas by the solution-polymerization method, a nanostructured powder with an average particle size of 33 nm was obtained. Electrical measurements were performed on sintered thick-films of the powders obtained by the three synthesis routes, exhibiting a p-type semiconductor behavior. The gas responses of the Bi10Co16O38 sensors to O2 and CO2 were markedly improved with the nanostructured film. Besides, the dynamic change of resistance at 425 °C showed an increase of about 103 Ω when exposed to CO2, suggesting that the nanostructured Bi10Co16O38 is a good candidate for environmental gas sensing.