Oxygen gas sensing behavior of nanocrystalline tin oxide prepared by the gas phase condensation method

Nanocrystalline SnO2 powders have been synthesized by the gas phase condensation method. The synthesis consists of the evaporation of commercial SnO powders in a He atmosphere with calcination at 573 K of the collected ultrafine powder. The material obtained shows a fractal texture and contains small amounts of SnO in addition to the SnO2 cassiterite phase. At a temperature up to 573 K the surface interacts with gaseous oxygen and the electrical conductivity (sigma)follows a law of the type: sigma = P-o2(-1/4). Th, response of sigma varies reversibly with the oxygen pressure and rather rapidly for a powder sample. This has been explained by a combination of a high surface area with very good electrical interconnections between grains. This last effect has been attributed to the nanocrystalline character of the particles, their high degree of coalescence, and to the presence of small amounts of quasi-metallic SnO in the present material. The exponential variation of sigma with temperature is evidence for the semiconductor character of the SnO2 nanocrystalline powder and allowed the determination of the enthalphy of formation of anionic vacancies. The electrical behavior of the stannic oxide sample has been compared with a commercial (Aldrich) SnO2 powder and the differences observed have been discussed. (C) 1997 Acta Metallurgica Inc.