PREPARATION, DEVELOPMENT OF MICROSTRUCTURE, ELECTRICAL AND GAS-SENSITIVE PROPERTIES OF PURE AND DOPED SNO2 POWDERS

The influence of bulk dopants (Nb, Mn, In and Pd) on the morphological, electrical and gas-sensing properties of SnO2 powders was observed. Comparing the specific surface areas of the powders observed by BET Nb-doping results in very fine powders. The electrical resistivity of SnO2 is decreased by Nb-doping and increased by bulk doping with either Pd, Mn or In. The existence of solid solutions in the systems doped with Nb, Mn and In is confirmed by single crystal experiments. The gas sensitivities are strongly correlated with the electrical resistivities of the sensor elements. The complex influence of dopants on the morphological and electrical properties of SnO2 is demonstrated by establishing a relation between the crystallite diameter, an evaluated carrier concentration, the number of electrons per crystallite and the thickness of the electron depletion layer. A limitation of bulk doping with electron-compensating elements for sensor optimization is given.