Sintering and electrical conductivity of doped WO3

The influence of a series of oxide additives, namely Al2O3, Co3O4, MnO2 and Na2O, on the sintering capacity and electrical conductivity of WO3-based binary ceramic systems was studied. The densification behaviour and the microstructures obtained after firing were dependent on the additive oxide type. A small addition of Na2O shifts the onset of sintering to lower temperatures, whereas the addition of Al2O3 shifts the onset of sintering to higher temperatures compared with undoped WO3. The inhibition of grain growth was observed in Al2O3-doped WO3. The electrical conductivity of these WO3 ceramics depends on the additive oxide type and varies in the range from 2 x 10(-2) to 9 x 10(-7) Omega(-1) cm(-1). The WO3-Na2O system was found to exhibit non-linear current-voltage characteristics and a low breakdown voltage. The non-linearity coefficient of the current-voltage characteristics of the Na2O-doped WO3 ceramics increases with sintering temperature and attains a maximum value of around 5.