Electromechanical Properties and Microstructure of Undoped K<sub>0.5</sub>Na<sub>0.5</sub>NbO<sub>3</sub> Ceramics and KNbO<sub>3</sub>-NaNbO<sub>3</sub> Crystals

K 0.5 Na 0.5 NbO 3 (KNN) was manufactured by spark plasma sintering (SPS), which is a fast sintering method allowing to control the grain growth. Different samples of KNN are sintered with SPS at 920°C under 50 MPa for 5 minutes. High densities over than 97% are achieved. In order to make domain engineering, KNN crystals are grown by floating zone method. Stable molten zone is reached when oxygen or nitrogen gas flux is used, leading up to 50 mm length of crystals. High electromechanical coupling factor kt about 46 %, kp around 45 % and ε33S/ε0 of 253 are achieved for KNN ceramics poled at optimum electric field about 3 kV / mm. KNN crystal boule exhibits kt about 40 % against 34 % for KNN ceramic, both poled at 1 kV / mm. These results are promising to replace PZT for transducers applications.