Preparation And Modification Of Potassium Sodium Niobate Based Lead-Free Piezoelectric Ceramics

(KxNa1-x)NbO3 (KNN) lead-free ceramics were prepared by the conventional solid-state sintering method, and their microstructures characterized by X-ray diffraction methods. The piezoelectric properties of the ceramics were determined by a piezoelectric constant d33 tester, and their electrical properties by precision impedance analyzers. The relationships between the components, phase transitions, and structures of pure KNN ceramics and doped into ZnO and LS with the piezoelectric properties and dielectric properties were assessed, and the main findings and conclusions are as follows:1. The sintering temperature and components of K2CO3 have a significant impact on the structure, density, piezoelectric and dielectric properties of the ceramics. The best performance, with d33=85pC/N;p= 4.184g·cm-3;εr(1kHz) =647, tan8(1kHz)=0.776, was obtained for x=0.5 and a sintering temperature of 1060℃.2. As a consequence of the poor sintering performance and high density of pure KNN ceramics, samples were doped into ZnO, and the relationships between composition and sintering temperature, crystal structure, microstructure, piezoelectric and dielectric properties of the KNN-xwt%ZnO ceramic system were investigated. With increasing sintering temperature, the d33 and density of the ceramic samples initially increased, and then decreased, whereas there was little influence of sintering temperature on Tc and To-t. The d33 and density of the samples also initially increased then decreased with increasing addition of ZnO, whereas the opposite behavior was observed for εr, Tanδ decreased, and To-t and Tc were shifted to lower temperatures. The best performance, with d33= 113pC/N, ρ=4.436g·cm-3, ε, (1kHz)=810.62, and tan8 (1kHz)= 0.0517 was obtained for a sintering temperature of 1100℃ and x=0.5 wt%.3. The relationships between composition and sintering temperature, crystalline structure, microstructure, piezoelectric and dielectric properties were also studied for (1-x)KNN-xLS ceramics.With increasing sintering temperature, the d33 and density of the samples also increased initially then decreased, and all samples had a dielectric peak. The best performance of d33=98pC/N,ρ=4.255g·cm-3,εr(10k)=554.95 was obtained when the ceramics were sintered at 1050℃. With increasing amounts of added LS, the d33, Tanδ and density of the ceramics all increased initially and then decreased, whereas ε decreased after a slight initial increase. At the same time, both To-t and Tc were shifted to lower temperatures with increasing LS contents.The KNN ceramics with 4at.% added LS had good piezoelectric properties of d33=108pC/N,p=4.18g.cm-3,εr(10k)=193.98, tan8(10kHz)=0.041 at a sintering temperature of 1050℃.