Study On Preparation And Properties Of （Ba, Ca）（Ti, Zr）O₃Lead-free Piezoelectric Ceramics

(Ba, Ca)（Ti, Zr）O₃（abbreviated as BCTZ） based lead-free piezoelectric ceramic is akind of A and B-site ion composite substituted ferroelectric. It was considered the mostlikely to replace the lead-based ceramic material, this is mainly because it has a highpiezoelectric properties at room temperature. In this thesis, BCTZ ceramics wereprepared successfully using a solid state reaction method. And we carried out asystematic study on BCTZ ceramics, the research content, see as follows:（1） The effects of Zr content （x=0-0.15） on the microstructure and electricalproperties of the (Ba_0.85Ca_0.15)(Ti_1-xZr_x)O₃（abbreviated as BCTZ） lead-free piezoelectricceramics were investigated. The results indicated that all the samples possess a pureperovskite phase structure. The phase structure of the sample changed from tetragonalphase to rhombohedral phase around room temperature with increased Zr content, andthe rhombohedral phase and tetragonal phase coexist in the composition range of0.05<x<0.1. Meanwhile, the piezoelectric constant d₃₃, planar electromechanicalcoupling factor k_p, remnant polarization P_rand dielectric constant ε_rfirst increased andthen decreased, the coercive field E_cdecreased with increasing the amount of Zr. Thecomprehensive properties of (Ba_0.85Ca_0.15)(Ti_1-xZr_x)O₃exhibits optimum value at x=0.08:d₃₃=461pC/N, k_p=50.7%, P_r=14.1μC/cm², E_c=4.1kV/cm and ε_r=3696.（2） The phase structure, dielectric and piezoelectric properties for(Ba_0.85Ca_0.15)(Ti_1-xSn_x)O₃（abbreviated as CBTZS-x） lead-free piezoelectricceramics with different Sn content were investigated in the composition range of0≤x≤0.1.It is found that all samples have a pure perovskite phase structure. With the increase ofSn content, the phase structure of the sample changed from coexistence of rhombohedraland tetragonal phase to tetragonal structure near room temperature. The temperature ofTR-Tand TCshifts towards lower temperature. When x=0.04, the TR-Tmore close to roomtemperature, which shows excellent piezoelectric properties. Meanwhile, the remnantpolarization P_rand coercive field E_cdecreased, but dielectric constant ε_rincreased withincreasing the amount of Sn. The CBTZS-x ceramic with x=0.04exhibits the optimalproperties: d₃₃=665pC/N, k_p=55.6%, ε_r=4520, P_r=1.6μC/cm²and E_c=12.5kV/cm, whichindicates that the CBTZS ceramic has a good application prospect.（3） Effects of Mn addition on the microstructure, dielectric and electromechanicalproperties of (Ba_0.92Ca_0.08)(Ti_0.95Zr_0.05)O₃-xmol%Mn （abbreviated as BCTZ-xMn）lead-free piezoelectric ceramics were investigated in the composition range of0≤x≤2.2. Itis found that, with the increase of Mn content, the phase structure of the sample changedfrom coexistence of orthorhombic and tetragonal phase to tetragonal structure near room temperature. And the piezoelectric constant d₃₃and planar electromechanical couplingcoefficient k_pdecrease with deviation from the polymorphic phase transition （PPT）region. Meanwhile, the Curie temperature TCgradually decreases with the increase of Mncontent. The relative high d₃₃, k_pand TCstill maintain about224pC/N,33.6%and102℃at x=2.0, respectively. Moreover, Mn doped BCTZ-xMn ceramics have an importantimpact on mechanical quality factor Q_mand dielectric loss tan δ. High mechanical qualityfactor of Q_m=921and low dielectric loss of tan δ=0.3%have been obtained at x=2.0.