Size effect and gas sensing characteristics of nanocrystalline xSnO(2)-(1-x)alpha-Fe2O3 ethanol sensors

Non-equilibrium nanocrystalline xSnO(2)-(1 - x)alpha-Fe2O3 powders have bee n prepared using the mechanical alloying technique. The thick film screen p rinting technology is then employed to fabricate these ethanol gas sensors. Their particle size and structural properties are systematically character ized using X-ray diffraction (XRD) and transmission electron microscopy (TE M). The gas sensing characteristics are also measured. Based on the experim ental results, we have observed that particle size of the powders is drasti cally milled down to about 10 nm after 24 h of high-energy milling. A very high gas sensitivity value of 845 for 1000 ppm of ethanol gas in air has be en obtained. Our proposed new structural model for these non-equilibrium na nocrystalline xSnO(2)-(1 - x)alpha-Fe2O3 materials explains both the lattic e expansion of these high energy mechanically alloyed powders as well as th e charge neutrality in terms of additional oxygen dangling bonds at the nan o-sized particle surfaces. It is those enormous oxygen-dangling bonds at th e particle surfaces that give rise to the high gas sensitivity. The sensors are found to be 32.5 times more selective to the ethanol gas compared to C O and H-2 gases. (C) 2000 Elsevier Science S.A. All rights reserved.