Study On Preparation And Properties Of （Ba,Ca）（Ti,Zr,Sn）O₃ Lead-free Piezoelectric Ceramics

BCTZ based lead-free piezoelectric ceramic was considered the most likely to replace the lead-based ceramic material,which is a kind of A and B-site ion composite substituted ferroelectric,mainly because it has a high piezoelectric properties at room temperature.In this thesis,BCTZ based ceramics were prepared using a solid state reaction method,and studied the modified BCTZ ceramics by doping effect and so on,the research content,see as follows:（1）Co₂O₃-doped(Ba_0.85Ca_0.15)(Ti_0.92Zr_0.08)O₃（BCTZ-xmol%Co,x=0～1.4）lead-free ceramics have been prepared by the solid-state method.The influence of Co₂O₃ content on the microstructure,dielectric and piezoelectric properties were investigated.The results show that all the samples possess a pure perovskite phase structure.With increasing of Co₂O₃ content,the grain size decreased gradually,together with the decrease of the dielectric constant εr,piezoelectric coefficient d33 and electromechanical coupling factor kP.Mechanical quality factor Qm improved significantly.The ceramic with x= 0.7 exhibits the optimum electrical properties,d33 = 392 pC/N,KP 46.0%,Qm＝435,tanδ=0.62%.As a result,the BCTZ-xCo ceramic is a promising candidate for lead-free piezoelectric ceramics.（2）Fe₂O₃-doped(Ba_0.85Ca_0.15)(Ti_0.90Zr_0.06Sn_0.04)O₃（BCTZS-Fe）lead-free ceramics were prepared by the conventional solid-state method.The influence of Fe₂O₃ content on the microstructure,dielectric,ferroelectric and piezoelectric properties are investigated.The results show that all the samples possess a pure perovskite phase structure.A small amount of doping can make the grain size growth and improve the electrical properties.With the doping of 0.025 Fe₂O₃,the BCTZS ceramics show the optimum electrical properties,piezoelectric constant d33 = 515 pC/N,electromechanical coupling factor Kp ＝48.2%,mechanical quality factor Qm= 182,2Pr= 18.2 μgC/cm2,2Ec = 4.3 kV/cm and permittivity εr = 5175.（3）(Ba_0.99Ca_0.01)(Ti_0.98Zr_0.02-xSn_x)O3 leed free ceramics were prepared by solid-state reaction method.The microstructure,dielectric and impedance properties of the samples were studied by XRD,SEM,and temperature dependence of dielectric and Cole-Cole plots.Wide ranges of frequency（40 Hz-3 MHz）and temperature（400～500℃）dependence of the dielectric and complex impedance spectroscopic were investigated,indicating that obvious frequency dispersion and relaxation above the TC temperature.The Cole-Cole plots show that both bulk and grain boundary affect dielectric relaxation in the material,conductivity follows Arrhenius behavior.The grain boundary activation energy Ea（gb）is greater than the grain activation energy Ea（g）,and the largest grain resistance Rg and the smallest grain boundary activation energy Ea（gb）were found at x =0.01 in the samples.