Abstract
Using oxide compositions is a promising method of increasing the sensitivity and selectivity of semiconductor gas sensors on the basis of SnO2, In2O3, WO3and other oxides. We have studied nanocrystalline tungsten oxide (WO3), indium oxide (In2O3), cobalt oxide (Co3O4) and mixed oxide compositions with different WO3/In2O3and WO3/Co3O4ratios synthesized using the sol-gel method after xerogel annealing at 400–600 °C. The morphology, phase composition and structure of the materials have been studied using X-ray diffraction, infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. We showed that stable structures can be produced in WO3–In2O3and WO3–Со3O4nanoheterogeneous compositions. The growth of grain size in WO3and In2O3, WO3and Co3O4during heat treatment of mixed compositions occurs slower than in simple oxides. An increase in the gas sensitivity of the compositions in comparison with simple oxides can be accounted for by smaller grain sizes and hence larger specific surface area, as well as by the dependence of grain surface state on material composition. Both compositions exhibit the greatest nitrogen dioxide response at 130–150 °C and the greatest carbon oxide response at above 230 °C. We have produced low-power nitrogen dioxide sensors with a sensitivity of << 1 ppm and power consumption of ≤ 85 mW.
Highlights
Using oxide compositions is a promising method of increasing the sensitivity and selectivity of semiconductor gas sensors on the basis of SnO2, In2O3, WO3 and other oxides [1]
Xerogel annealing at 400 and 600 °C for 2 h in the WO3–In2O3 system led to the formation of a heterogeneous two-phase material consisting of a monoclinic WO3 phase and a cubic In2O3 phase
Annealing at 400 °C for 2 h in the WO3–Co3O4 system led to the formation of a heterogeneous two-phase material consisting of a monoclinic WO3 phase and a cubic Co3O4 phase and annealing at 600–650 °C led to the synthesis of CoWO4 [3]
Summary
Using oxide compositions is a promising method of increasing the sensitivity and selectivity of semiconductor gas sensors on the basis of SnO2, In2O3, WO3 and other oxides [1]. Earlier [2,3,4,5] the structure and morphology of WO3–In2O3 and WO3–Co3O4 oxide compositions synthesized using the sol-gel method were studied. Xerogel annealing at 400 and 600 °C for 2 h in the WO3–In2O3 system led to the formation of a heterogeneous two-phase material consisting of a monoclinic WO3 phase and a cubic In2O3 phase. Annealing at 400 °C for 2 h in the WO3–Co3O4 system led to the formation of a heterogeneous two-phase material consisting of a monoclinic WO3 phase and a cubic Co3O4 phase and annealing at 600–650 °C led to the synthesis of CoWO4 [3]. Haiduk YuS et al: Structure and gas sensitivity of WO3–In2O3 and WO3–Co3O4 with source simple oxides and an increase in the specific surface area of the material. We analyze experimental data on the structure and morphology of the abovementioned compositions annealed at 200–600 °C and the СО and NO2 sensitivity of the specimens as a function of composition and temperature
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