Synthesis,microstructure and electromechanical properties of undoped (K 0·5 Na 0·5 )NbO 3

Abstract

Conventional solid state mixed oxide route using manual and ball milling is investigated for the preparation of K_0·5Na_0·5NbO₃ (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 k_t (33 to 48%), k_p 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.