Study On Modifing And Sintering Properties Of Sodium Niobate Based Lead-free Piezoceramic Ceramics

In this paper, study on chemical composition modification and sintering properties ofKNN-based ceramics by a conventional solid-state reaction route was carried out. Firstly, influenceson electrical properties of lead-free KNN+1mol%ZnO+x mol%CuO ceramics were investigated.CuO and ZnO co-doped assisted the densification of KNN piezoceramics, and significantly decrasedthe optimal sintering temperature. The volatilization of the alkali metal elements can be reduced atlower temperature. The mechanical quality factor Qmcould significantly be improved for “hardening”effect of the Cu²⁺-doped. For the ceramics with x=1.5, the best performance of piezoelectric ceramicwas obtained. Influence of sintering temperature on electric properties of KNN+1mol%ZnO+1.5mol%CuO ceramics was also studied. Liquid phase may be present during the sintering process. Theaverage grain sizes of the ceramics became larger with increasing sintering temperature.Secondly, the piezoelectric properties of CuO and ZnO co-doped KNN ceramics are not verywell. The piezoelectric properties of KNN ceramics can be improved by Li, Sb, Ta co-doping.According to previous works, electrical properties of (K_0.4425Na_0.52Li_0.0375)(Nb_0.93-xTa_xSb_0.07) O₃piezoceramics were investigated with an emphasis on the influence of Ta content. All the ceramics aresingle perovskite phase with tetragonal symmetry. A relatively homogeneous microstructure can beseen at x=0.06. The results indicate that Ta substitution provided “soft” piezoelectric characteristics,owing to improvements in d33, kpand a decease in Qm. Curie temperature TCshift towardlower-temperature regions by increasing the content of Ta, and Ta would weaken the ferroelectricityof the ceramics. The optimal performance of piezoelectric ceramic was obtained at x=0.06. Influenceof sintering temperature on densification and electric properties was also investigated.Lastly, CuO was added to the(K_0.4425Na_0.52Li_0.0375)(Nb_0.93-xTa_xSb_0.07) O₃ceramics to enhance Qm,and the microstructure and electromechanical properties were systematically investigated. AfterCuO-doped, a dense microstructure with increased grains is developed, probably due to liquid-phasesintering. The tetragonality of the ceramics slightly increased with increasing CuO content. Themorphology of ceramic particles significantly changed with the increase of CuO. The results of thiswork suggest that both ‘‘hard’’ and ‘‘soft’’ effects were observed due to Cu²⁺addition, whichenhanced the Qmand kp, and reduced the piezoelectric coefficient d33, Ec, εrand tanδ. Besides, it isfound that the tetragonality of the ceramics increased with raising sintering temperature.