Preparation And Performance Study Of Ca Doping KNN-based Lead-free Piezoelectric Ceramics

Lead zirconate titanate?PZT?based ceramics are still the most widely used piezoelectric materials until now owing to their excellent piezoelectric properties and large scale production capability.As the core components:ZT piezoelectric ceramics have been widely used in devices of ultrasonic motors,sensors and transducers.However,the lead is toxic and seriously threatens human health and environment.From the view point of green development,hazardous substances have been restricted in electrical and electronic equipment by related laws and regulations in many regions and nations.Therefore,tremendous work has been devoted to develop a series of lead-free piezoelectric materials to replace the PZT ceramics.KNN-based ceramics have drawn much more attention because of their remarkable piezoelectric efficient(d₃₃)and high Curie temperatures?T_C?.In this paper,doping modification was used to improve the piezoelectric properties of KNN-based ceramics.In this work,three KNN-based ceramics systems were prepared by conventional solid-state sintering method:(K_0.48,Na_0.52)NbO₃-0.05Ca_x(Bi_0.5,Na_0.5)_1-xZrO₃;?1-x?(0.96(K_0.48,Na_0.52)NbO₃-0.04(Bi_0.5,Na_0.5)ZrO₃)-xCaSnO₃ and(K_0.48,Na_0.52)(Nb_?1-x?Sb_x)O₃-0.05Ca_0.2(Bi_0.5,Na_0.5)_0.8ZrO₃.By the method of XRD,SEM,the impedance analyzer,the effect of dopant on the phase structure,microstructure and electrical properties of the KNN-based ceramics were systematically investigated.The main research results:In the first part,Ca was used as dopant to modified KNN-CxBNZ ceramics.Rhombohedral-orthorhombic?R-O?and orthorhombic-tetragonal?O-T?phase coexistence has been obtained in the composition range of0.15?x?0.3;appropriate Ca?x?0.2?content promotes the grain growth,which leads to a denser microstructure;with the increase of Ca content,Curie temperature?Tc?of the ceramics without a conspicuous change.The ceramics with x=0.2 possess enhanced piezoelectric properties:d₃₃³08pC/N,k_p⁴9.0%,?_r=1431;tan?=3.57%;Tc=328°C.Second part:CaSnO₃ was used as dopant to modified?KNN-BNZ?-xCS ceramics.The R-O&O-T phase boundaries at room temperature has been verified in 0.075?x?0.15;the doping of CaSnO₃ leads the ceramics bimodal grain distribution;the max remanent polarization of?KNN-BNZ?-xCS ceramics was Pr=21.98?c/cm²;The optimized piezoelectric properties of?KNN-BNZ?-xCS ceramics was obtained in x=0.125:d₃₃=370pC/N,?_r=1225,kp=43.5%,tan?=3.1%,Tc=313oC.In the third part,in order to build MPB of R-T,Sb was used to modified the KNN-CBNZ ceramics:KNNSx-CBNZ ceramics.The rhombohedral?R phase?and tetragonal phase?T phase?boundaries were obtained in x?0.03;the addition of Sb made the grains size tend to be homogenization;with the increase of the Sb content,Curie temperature decreases significantly;KNN-CxBNZ ceramics possessed prominent piezoelectric performance in the morphotropic phase boundary?MPB?and the optimistic was obtained in x=0.03:d₃₃=470 pC/N,tan?=3.3%,T_C=243°C,k_p=52.4%.