Effect of orthorhombic phase on hydrogen gas sensing property of thick-film sensors fabricated by nanophase tin dioxide

Abstract

Nanophase metallic tin powder was synthesized by an inert gas condensation method and subsequently oxidized into two types of SnO 2 by two heat-treatment routes: (1) after annealing up to 900 °C in air, the synthesized powder was oxidized to form a mixture of tetragonal and orthorhombic SnO 2, and (2) the synthesized powder was transformed into an amorphous tin oxide by intermediate annealing at 225 °C. The amorphous tin nano-particles were oxidized into a single phase of tetragonal SnO 2 during heat treatment up to 900 °C in air. The sensitivity of the sensors fabricated from two types of nanophase SnO 2 powders was evaluated by means of electrical resistance measurements. The thick-film sensors fabricated by the mixed SnO 2 powder exhibited a lower sensitivity to hydrogen than those fabricated by the single tetragonal SnO 2 powder. TEM observations and EPR measurements were carried out in order to interpret the role of the orthorhombic phase in gas sensing. The detrimental effect of orthorhombic SnO 2 on the sensitivity was attributed to an increased number of planar defects in the microstructure and a change in species of oxygen absorbents on the surface layer of the SnO 2.