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. Tungsten oxide (WO3) with nano and micron particles was used as a donor dopant. 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. SEM results revealed that micron WO3 inhibited the grain growth of KNN ceramics and led to a finer microstructure. KNN with micron WO3 had much finer microstructure and the sintering process terminated at higher temperature compared to pure KNN and KNN with nano WO3. Nano and micron sized WO3 affected the densification and electrical properties of KNN considerably. Additionally, KNN with nano WO3 reached the maximum density at lower temperature compared to its counterpart. Finally, at 1125ºC KNN with 0.3 mol% nano sized WO3 showed d33, εr, tanδ, and Qm of 75 pC/N, 345, 2%, and 50, respectively. For KNN sample with 0.3 mol% micron WO3 at 1135°C these values were 81 pC/N, 773, 3.3%, and 30, respectively.