Microstructure and conductivity of short duration sintered tin oxide ceramics

Abstract

Microstructure and conductance of pure tin oxide specimens were investigated. For the manufacture of the material, 10-min sintering at peak temperatures of 500–1300°C was used. It was noticed that the microstructural characteristics for the material sintered at 1300°C were remarkably different from the materials sintered at lower temperatures. Both the average particle size and the average pore size were essentially larger in this material. Specific surface area was correspondingly smaller. As for the sintering process, electron micrographs together with pore size measurementssupport the view that pores are coarsening within a framework of coalesced particles. Conductance measurements showed pronounced non-ohmic behaviour at low test temperatures. On the basis of this non-ohmic conductance it was considered that in the materials studied, energy barriers rather than necks with open current paths control the current. The results were interpreted as the dependence of current on voltage based on the model of chain-like barrier combinations. It was also concluded that significant energy barriers do not appear at all of the particle boundary surfaces. Results obtained in this work can be utilized in the development of working models of semiconductor gas sensors. On the basis of the results it can also be concluded that in gas sensors manufactured from tin oxide, suitable additional oxides might need to be used so as to control the growth of contact areas between the particles.