KN-based Lead-free Ferroelectric Materials for SONAR applications

(Ba0.85Ca0.15)(Ti0.90Zr0.10)O3 ceramic was synthesised using the mixed oxide method. The full piezoelectric matrix of the device was characterised and the material was machined and used in two types of transducer device. The receive sensitivity and transmit voltage response of the device was then measured.
The synthesis of pure KNbO3 by the mixed oxide method was optimised to reduce potassium loss. Solid solutions of (1-x)KNbO3-xCaZrO3, (1-x)KNbO3-xLiNbO3 and (1-x-y)KNbO3-xCaZrO3-yLiNbO3 were synthesised. The aim was to replicate the mixed of phases found in PZT and BCTZ. Substituting KNbO3 with CaZrO3 induced a rhombohedral phase to appear at room temperature when x=0.03, making a mixed phase of orthorhombic and rhombohedral. CaZrO3 decreased the TO-T and TT-C phase transitions. Substituting KNbO3 with increasing amounts of LiNbO3 initially reduced the TO-T before inducing a secondary phase. LiNbO3 also acted as a sintering aid, which allowed high electric field measurements. The d33* of the solid solution peaked when x=0.07.
Combining both solid solutions the individual effects of each system was repeated. Increasing the fraction of CaZrO3 induced a rhombohedral phase at room temperature and increasing the fraction of LiNbO3 improved the sinterability and overall piezoelectric performance.