Synthesis, microstructure and electromechanical properties of undoped (K _0·5 Na _0·5 )NbO ₃

Conventional solid state mixed oxide route using manual and ball milling is investigated for the preparation of K0·5Na0·5NbO3 (KNN) ceramics. Microstructure engineering was made using two milling methods and sintering techniques, and the crystal growth; then electromechanical properties were investigated as a function of sintering temperature, densification and grain size. The sintering conditions were set at 920°C/5 min for spark plasma sintering and 1090–1120°C/10 and 48 h for classical sintering. KNN crystal was grown using floating zone technique under nitrogen gas, where the translation and rotation speeds were fixed at 3 mm h−1 and 20 rev min−1 respectively. Piezoelectric and dielectric performances were measured and related to the microstructure. High kt (33 to 48%), kp of 18 to 48% and d33 of 127–140 pC N−1 were reached for relative densities of 84 to 96%. KNN ceramics are now available for the design of ultrasonic sensors.