Effect of nano and micron WO3 on microstructure and electrical properties of lead free potassium sodium niobate piezoceramics

Lead free potassium sodium niobate (KNN) piezoceramics were synthesized via conventional solid state sintering route. Nano and micron WO3 were separately added to KNN through ball-milling. Dielectric and piezoelectric properties of samples sintered in the temperature range of 1110°-1145°C were measured by precision LCR-meter and APC d33-meter devices. The results revealed that micron WO3 particles were effective in inhibiting the grain growth in KNN ceramics. Micron WO3-added KNN obtained much finer microstructure and the sintering process terminated at higher temperature compared to pure KNN and nano WO3-added KNN. Densification and electrical properties of KNN were considerably affected by using nano and micron WO3. Nano WO3-added KNN obtained its maximum density at lower sintering temperature compared to micron WO3-added KNN. With increasing the sintering temperature over optimum amounts, the density of both WO3-added KNN samples decreased due to the evaporation of alkalis. Finally, at 1125ºC KNNW3n showed d33, εr, tanδ, and Qm of 75 pC/N, 345, 2%, and 50, respectively. For KNNW3m sample at 1135ºC these values were 81 pC/N, 773, 3.3%, and 30, respectively.