Research On The Piezoelectric Properties Of Titanate Based Lead-free Piezoelectric Ceramics

Lead-free piezoelectric ceramics （1-x）Bi_0.5(Na_0.84K_0.16)_0.5TiO_3-xBa_0.77Ca_0.23TiO₃（BNKT-xBCT, x=0⁰.04） were synthesized by conventional solid state reaction method. The piezoelectric,dielectric and ferroelectric characteristics of the ceramics are investigated and discussed. The XRDresults show that Ba0.77Ca0.23TiO₃（BCT） has diffused into Bi_0.5（Na0.84K0.16）_0.5TiO₃（BNKT） latticesto form a new solid solution. The piezoelectric measurements and P-E hysteresis loops reveal thatBNKT-0.025BCT ceramic has the highest piezoelectric performance and strongest ferroelectricityin all the samples. Piezoelectric constants d33, kpand ktof175pC/N,29.1%and54%are achieved.Remnant polarization Prand coercive field Ecreach28.3μC/cm2and24.2kV/cm, respectively.In order to create A-site vacancy in lead-free piezoelectric ceramics Bi_0.5(Na_0.82K_0.18)_0.5TiO₃,non-stoichiometric ceramics Bi_0.5+x(Na_0.82K_0.18)_0.5-3xTiO₃and Bi_0.5+y(Na_0.82K_0.18)_0.5TiO₃weresynthesized by a conventional solid state reaction method. This investigation reveals that moderateA-site vacancies in the prepared ceramics enhance the piezoelectric performance of the ceramics.Bi_0.505(Na_0.82K_0.18)0.485TiO₃ceramic possesses the highest piezoelectric properties and strongestferroelectricity: piezoelectric coefficient d33=151pC/N, electromechanical coupling factor kp=29.8%, mechanical quality factor Qm=124, remnant polarization Pr=29.5μC/cm2, coercive fieldEc=33.9kV/cm. The depolarization of the BNT-based ceramics might be caused by phasetransition from long-range ferroelectric to ergodic relaxor near Td.A-site vacancies were created in lead-free piezoelectric non-stoichiometric ceramicsBi_0.5+x（Na1-yKy）_0.5-3xTiO₃, which were synthesized by conventional solid state reaction process. Theresults show that moderate A-site vacancies in the prepared ceramics enhance the piezoelectricperformance of the ceramics. A large bipolar strain of0.35%is obtained inBi₍0.505(Na_0.74K_0.260.485TiO₃ceramic at room temperature. This ceramic is a promising candidate forpiezoelectric actuators.