Study On Doping Modification And Sintering Characteristics Of PZN-PZT Ternary Piezoelectric Ceramics

The PZN-PZT ternary system is widely used in electronic information and measurement fields due to its higher Curie temperature(Tc)and piezoelectric properties(d33)than the PZT binary system,such as various actuators,sensors,transducers and energy harvesters.In this paper,CeO2-doped 0.3Pb(Zn1/3Nb2/3)O3-0.7Pb(Zr0.52Ti0.48)O3+x wt.%CeO2(abbreviated as 0.3PZN-0.7PZT-xCe)and MnO2-doped 0.3Pb(Zn1/3Nb2/3)O3-0.7Pb(Zr0.52Ti0.48)O3+x wt.%MnO2(abbrevi ated as 0.3PZN-0.7PZT-xMn)piezoelectric ceramics were prepared by conventi onal solid state reaction method.The effects of dopant concentration and sinter ing temperature on the phase composition,microstructure and electrical properti es of the ceramics were studied.The main contents are as follows:1.The effects of MnO2 doping(x=0～1 wt.%)on the phase structure and electrical properties of PZN-PZT piezoelectric ceramics were studied.PZN-PZT ceramics still have a single perovskite structure after doping with MnO2.The addition of MnO2 can promote the sintering of ceramics to make the grains develop well,reduce the pores and increase the density.After MnO2 is incorporated into the perovskite lattice of PZN-PZT,it will change its valence to Mn3+,thereby replacing its B-site(Zr/Ti)4+,causing lattice distortion and having a ’hard doping’ effect.When the doping amount of MnO2 is 0.5 wt.%,the mechanical quality factor of the ceramics is the highest(Qm=369),and the dielectric loss is the lowest(tan δ=0.6%).2.The effects of CeO2 doping(x=0～0.5 wt.%)on the phase structure and electrical properties of PZN-PZT piezoelectric ceramics were investigated.The PZN-PZT ceramics are still single perovskite structure after doping CeO2,indicating that the dopant diffuses into the perovskite lattice and forms a good solid solution with it.The diffraction peak near 2θ=44.5° splits into three characteristic peaks:(200)T,(200)R,(002)T,indicating that the system consists of rhombohedral and tetragonal phases.When x=0.2,the ratio of the two phases is close to 1:1.A small amount of CeO2 doping(x≤0.2)has a significant ’soft doping’ effect;however,excessive CeO2 doping(x>0.2)shows a certain ’hard doping’ effect(Ce3+acceptor replaces B-site(Zr/Ti)4+ions),which is due to the variable valence characteristics of cerium ions in solid solutions.The study of ferroelectric hysteresis curve(P-E)further proves that a small amount of CeO2(x≤0.2)doping makes the ceramics ’soften’(the coercive field Ec decreases),and the ferroelectric domain is easier to flip(the residual polarization Pr increases).When x=0.2,the PZN-PZT ceramics sintered at 1210℃have the best properties:d33=480 pC/N,kp=68%,TC=297℃,tan δ=1.6%,Ec=1.02 kV/mm,Pr=38.3 μC/cm2.3.The effects of sintering temperature(1190℃～1260℃)on the phase structure and electrical properties of 0.3PZN-0.7PZT-0.2Ce piezoelectric ceramics were studied.When the sintering temperature is lower than 1230℃,the ceramic is a single trigonal phase.When the sintering temperature is higher than 1250℃,it is completely transformed into tetragonal phase.As the sintering temperature increases,TC gradually increases and tan δ decreases.Increasing the sintering temperature also helps to improve the d33 and kp of the ceramics,but too high sintering temperature(1260℃)will also deteriorate the electrical properties of the ceramics.The sample sintered at 1250℃ has the best electrical properties:TC=293℃,d33=515 pC/N,kp=67%,εr=2493,TKε(120℃)=6.22×10-3/℃,tan δ=2.4%.