Structure and gas-sensitive properties of WO3-Bi2O3 mixed thick films

WO3-Bi2O3 mixed screen-printed thick films with various Bi2O3 contents (3-50 wt.%) have been studied as a promising sensitive material for NO gas sensors. It has been revealed that the Bi2O3 influence on gas-sensitive electrical properties of the mixed thick films is ambiguous and depends strongly on Bi2O3 content. WO3-Bi2O3 (3 wt.%) thick films are more sensitive to NO than pure WO3 thick films. On the other hand, further increasing of the Bi2O3 content in the mixed films leads to decreasing of their NO sensitivity. The structure of the films has been studied by XRD and SEM. It has been demonstrated that the microstructure of the mixed films depends vastly on the Bi2O3 content. An interpretation of the Bi2O3 influence on the microstructure formation process of the mixed thick films is proposed. Thereupon the difference in NO sensitivity of the investigated films is explained. An optimal composition of WO3-Bi2O3 sensitive elements for NO sensors has been determined. (C) 2000 Elsevier Science S.A. All rights reserved.