Study On The Improved Properties Of PNN-PHT Based Piezoelectric Ceramics By Doping

Piezoelectric ceramics,which have excellent piezoelectric,dielectric and ferroelectric properties,have been widely used in actuators,multilayer capacitors,sensors and transducers.However,the requirement of high piezoelectric property and Iow sintering temperature restricts their further application.Therefore,piezoelectric ceramics with both high piezoelectricity and low sintering temperature have broad research prospects.The literatures and our previous study showed that the Pb(Nb,Ni)O3-Pb(Hf,Ti)O3(PNN-PHT)ternary piezoelectric ceramics with perovskite structure have excellent piezoelectric properties,which are expected to become a high piezoelectric ceramic material.In this paper,PNN-PHT ternary piezoelectric ceramic materials were studied,and their properties were improved by single ion doping,sintering aids and ion co-doping.The main contents and conclusions are as follows:Fe2O3-doped 0.49Pb(Ni1/3Nb2/3)O3-0.51Pb(Hf0.3Ti0.7)O3 piezoelectric ceramics were prepared by the traditional solidstate method.A systematic study of Fe2O3 doping on the microstructure,piezoelectric and dielectric properties of 0.49Pb(Ni1/3Nb2/3)O3-0.51Pb(Hf0.3Ti0.7)O3 ceramics was performed.Results showed that Fe3+ cations could dissolve into the B-sites of the PNN-PHT crystal and benefited for the formation of pure perovskite structure.Meanwhile,Fe doping caused a significantly enhance in the piezoelectric and dielectric properties.The better piezoelectric properties,1.e.d33=960 pC/N,?r=6734,kp=0.62 and Tc=133?,were achieved for the samples doped with 1.0 at%Fe2O3.Through the first-principles calculation and PFM observation,it was found that mesoscopic domains contributed mainly to the high piezoelectric properties of samples,which were tailored by defect dipoles from pristine domains.In order to improve the piezoelectric properties and sintering characteristics of PNN-PHT ceramics,the effect of LiF addition on the microstructures and piezoelectric properties of 0.49Pb(Ni1/3Nb2/3)O3-0.51Pb(Hf0.3Ti0.7)O3 ceramics was investigated in detail.Results showed that LiF addition with appropriate amount facilitated the formation of pure perovskite phase and promoted the densification of the PNN-PHT ceramics,which resulted in the increase in piezoelectric properties of the as-prepared samples.It was found that with the increase of sintering temperature,the ceramic sample become dense,and the grain enlarged.The better piezoelectric properties,i.e.d33=980pC/N,?r=7113,kp=0.57,tan?=0.023 and Tc=117?,were obtained for the 4 at%LiF added sample which was prepared at a sintering temperature as low as 1100? for 2h.Fe2O3 and Bi2O3 co-doped 0.49Pb(Ni1/3Nb2/3)O3-0.51Pb(Hf0.3Ti0.7)O3 ceramics were prepared by conventional solid state route.Results showed that through co-doping of Fe2O3 and Bi2O3,the crystal structure was changed from the rhombohedral phase to tetragonal phase for PNN-PHT ceramic.The doping promoted the formation of better microstructure and improved the piezoelectric and dielectric properties of the sample,and significantly reduced the sintering temperature.The better piezoelectric properties,i.e.d33=856pC/N,kp=0.60,?r=6500 and tan?=0.025 were obtained for the samples with 2at%Fe2O3 and 2at%Bi2O3,when sintered at 1050?.