High electromechanical performance with spark plasma sintering of undoped K0.5Na0.5NbO3 ceramics

Lead free piezoelectric K0.5Na0.5NbO3 (KNN) is synthesised by the conventional solid state mixed oxide route using dry ball milling. Spark plasma sintering technique (SPS) is an original and fast method which enables the grain growth to be controlled and allows to decrease a potential alkali volatilisation. Undoped KNN are sintered by SPS in the 920-975 degrees C temperature range, for dwell times of 5-15 min. The density range is 93-97%. Density, grain size and composition of samples are comparatively analysed. Electromechanical performances are measured and related to the microstructure. High planar coupling coefficient k(p) of 48%, thickness coupling factor k(t) of 45%, dielectric constant at constant strain epsilon(S)(33)/epsilon(0) of 328, and low mechanical losses delta(m) of 2% are reached for undoped KNN. These results are promising and suitable for transducer applications. (c) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.