Preparation And Performance Study Of BZT-BCT Lead-free Ferroelectric Ceramics

Functional ceramic materials have excellent properties of electric,magnetic,optical,acoustic and thermal,they play an important role in microelectronics,sensor,information communication,medical,energy,military and other advanced technical fields.Functional ceramic materials are indispensable basic materials in the current development of electronic science and information technology.Perovskite ceramic BaTiO₃ is one of the earliest studied,most widely studied and used electronic ceramic materials,and is called“The pillar of electronic ceramic industry”.However,low piezoelectic and dielectic properties and low Cure temperature?Tc,120 ^oC?of BaTiO₃ ceramic limit its application range.In recent years,people have improved the dielectric,piezoelectric,electrocaloric?EC?,electro-optic and other properties of BaTiO₃-based ceramics through doping modification of A-site or B-site,and achieved gratifying results,which makes BaTiO₃-based ceramics as lead-free piezoelectric materials have received extensive attention again.In this paper,?1-x?Ba(Zr_0.2Ti_0.8)O₃-x(Ba_0.7Ca_0.3)TiO₃[?1-x?BZT-xBCT]powders were synthesized by the conventional solid-state reaction method and the ceramics were fabricated by atmosphere and Hot-press sintering technology.The impact of powder preparation process,contents of BCT,doping of rare earth elements on phase structures,microstructures and ferroelectic,piezoelectric,dielectric,electrocaloric properties of BZT-BCT ceramics were investigated.The results show that with increasing ball-milling speed,the average particle size was decrease;when the speed of ball-milling is 1500 r/min the phase purity of BZT-BCT powder is the highest,the density of BZT-BCT ceramic is the highest,and the ferroelectric and dielectric properties are the best.The Tc shifts to higher temprature,P-E loop being fat,relaxor ferroelectric propeties is weaken and ferroelelctric propeties is strengthen,dielectric permittivity and EC temperature change are incraease first then decrease with the increasing contents of BCT.When BCT-doping content is 50%,ceramic shows best ECE and maximum permittivity.With the increase doping of rare earth elements La and Sm,the Tc of BZT-BCT ceramics decreases,relaxation characteristics increase,and the relative dielectric increases first and then decreases.When La-doping content is 2 mol%,Sm-doping content is 2.5 mol%,the relative dielectric is the largest.ECE of 50BZT-50BCT ceramic was measured by direct and indirect methods.The EC temperature change?T increase with increasing electric field,and increase first and then decrease with increasing temperature.The maximum?T_EC measured directly is 0.464 K at100 ^oC?Tc?and 6 kV/mm.Besides,50BZT-50BCT ceramic has fast response speed?1-3s?,wide working temperature range?80-140 ^oC?,and high stability and reliability.The effects of electric field and temperature on leakage current,Joule heat and ECE of material are systematically analyzed by practical measurement and theoretical calculation,respectively.The negative effect of Joule heat generated by leakage current on EC refrigeration is proved with the increase of electric field and temperature.Based on this,the intrinsic ECE and effective ECE are discussed,and the effective temperature change?T_effff of ECE is defined,which provides good guidance for the accurate characterization of ECE in EC materials.