Effects Of B-site Doping On Properties Of (K_0.5Na_0.5)NbO₃ Lead-free Ceramics

For decades,lead zirconate titanate(Pb(Zr1-xTix)O3 or PZT)ceramics have been widely used in various applications such as actuators,sensors,and transducer materials due to their excellent electric properties,However,PZT ceramics contain 60%of toxic Pb,the use of those ceramics has represent serious hazards to the environment owning to the process of preparation and improper disposal.Therefore,it's urgent to research and develop the lead-free piezoelectric ceramics to replacing the PZT ceramics,(K0.5Na0.5)NbO3(KNN)ceramics are widely studied on account of its good piezoelectric properties and high Curie temperature.In this paper,the powders were prepared by molten-salt method using Na2CO3 and K2CO3 as molten salts,the synthesizing temperature,holding time and the mass raito of molten salts and product of powders were optimized.The sintering temperature of KNN ceramics was optimized.The influence of Ta5+ions and Bi2O3-Nd2O3 on the phase,microstructure and electroproperties were studied.The result shows:KNN ceramics powders were prepared under 750? for 2 h when the mass raito of molten salts and product was 1:1 by molten-salt method;KNN ceramics were sintered at different temperatures by a pressureless sintering method,the KNN ceramics shown good properties when sintered at 1120?:d33?106 pC/N,Kp?0.24,?r=334.40,tan?=0.04,Pr=14.76?C/cm2,Ec=12.86 kV/cm,Tot?194 ?and Tc=405?.The doping of Ta5+ increased the sintering temperature and improved the electric properties of KNN ceramics,which also reduced the phase-transition temperature.The optimized content of Ta5+was 0.2 mol,(K0.5Na0.5)Nb0.8Ta0.2O3 ceramics shown excellent properties when sintered at 1160?:d33?134 pC/N,Kp?0.32,?r?342.50?tan?-=0.04,Pr=15.79?C/cm2?Ec?14.15 kV/cm,Tot?138? and Tc?302?,The Bi2O3-Nd2O3 was added in(K0.5Na0.5)Nb0.8Ta0.2O3 ceramics.The addition of Bi2O3-Nd2O3 improved the dielectric and ferroelectric properties,which also increased the Curie temperature,the optimized content was 1 mol%.When the content of Bi2O3-Nd2O3 was 1 mol%,the ceramics had the following properties:d33=104 pC/N?Kp=0.20,?r=434.52,tan?=0.04,Pr=17.84 ?C/cm2,Ec=18.58 kV/cm,Tot?117? and Tc?351?.