Dependence of the microstructure and electrical properties of tungsten oxide ceramics on synthesis conditions

Abstract

The influence of synthesis conditions on the microstructure and electrical properties of tungsten oxide (WO₃) ceramics is investigated. It is established that pure tungsten oxide undergoes a solid-state sintering process, and the onset temperature of densification decreases significantly after mechanical milling of the powder. This effect is attributed to the increase in Gibbs surface energy with decreasing particle size, which thermodynamically promotes sintering at lower temperatures. The density of ceramics sintered at 1200 °C for 2 h is found to be approximately 5.8 g/cm³, corresponding to about 80 % of the theoretical density. Scanning electron microscopy reveals a homogeneous microstructure with an average grain size of about 10 μm and no detectable secondary phases. Differential thermal analysis shows a sequence of phase transitions (γ → β → δ → ε → WO_3−x) associated with changes in defect structure and oxygen stoichiometry. Electrical measurements demonstrate nonlinear current–voltage characteristics similar to those of varistor materials, which are attributed to the formation of intergranular potential barriers. With increasing sintering temperature, the nonlinearity coefficient increases while the low-field conductivity decreases, indicating the strengthening of barrier effects at grain boundaries. The results confirm the potential of pure WO₃ceramics as a base material for varistor and composite systems with nonlinear electrical behavior.