Effect Of Grain And Phase Boundary On The Properties Of Barium Zirconate Titanate-based Lead-Free Piezoelectric Ceramics

Piezoelectric materials can achieve mutual conversion between mechanical energy and electric energy.Piezoelectric ceramics are relatively widely used due to their relatively excellent properties and simple preparation process.Piezoelectric ceramics can be divided into lead-based and lead-free piezoelectric ceramics.PbO,which is harmful to the human body and the environment,is formed during the preparation of widely used lead-based piezoelectric ceramics.Therefore,it is necessary to study lead-free piezoelectric ceramics to replace lead-based piezoelectric ceramics.Among the lead-free piezoelectric ceramic systems,BaTiO₃（BT）-based piezoelectric ceramics are widely used due to their high piezoelectric properties.Among them,（1-x）BaZrO₃-x BaTiO₃（BZ-xBT）ceramics exhibit excellent piezoelectric properties.The electrical properties of piezoelectric ceramics can be enhanced by constructing phase boundary,except for phase boundary,crystal grains also have a great influence on the electric properties of ceramics.In this paper,starting from the research background of BZ-xBT ceramics at home and abroad,the solid state reaction method is used to prepare BZ-xBT ceramics.The research results are as follows:The traditional solid state reaction method is used to prepare BZ-xBT（x=0.82～1）ceramics.Studying the relationship between the composition（BT content）and structure and properties of BZ-xBT ceramics under a narrow composition span（Δx≤0.02）.It is found that with increasing BT content（x）,the mean grain size（ξ）for BZ-xBT ceramics basically increases from～9μm（x=0.82）to～40μm（x=1）.The phase structure of ceramics,when x=0.82～0.88,BZ-xBT ceramics are rhombohedral phase（R）.when x=0.9～1,BZ-xBT ceramics show the coexistence of tetragonal phase（T）,orthorhombic phase（O）and R phase.For the electric properties of BZ-xBT ceramics,with increasing x,the peak dielectric constant（ε_m）,maximum polarization（P_m）,remnant polarization（P_r）,piezoelectric coefficient(d₃₃),electromechanical coupling coefficient（k_p）,electric energy density（W）,energy storage density(W_rec)and energy loss density(W_loss)have been improved,while the diffuseness factor（γ）and the energy storage efficiency（η%）decreased.It is worth noting that the electric properties of ceramics andξshow nearly the same changing trend with increasing x.The method of controlling the milling time and sintering conditions（sintering temperature and time）is used to control the grain size of BZ-0.96BT ceramics to study the influence of the grains on the electric properties of ceramics.Theξof the BZ-0.96BT ceramics prepared by changing the process is between 2μm and 102μm,all BZ-0.96BT ceramics have a coexisting structure of T+O phase.Regarding the relationship between the grain size and the electric properties of ceramics,the increase ofξof ceramics is conducive to the improvement ofε_m,P_m,P_r,d₃₃,and W_loss,and the dielectric constant（ε_r）,the temperature corresponding toε_m（T_m）,γ,E_c,W_rec,W andη%decrease.When theξof the ceramics exceeds 40μm,the electric properties of the ceramics basically no longer change asξcontinues to increase.The phase boundary of BZ-0.96BT ceramics is controlled by trace Fe doping to study the influence of phase boundary on the electric properties of ceramics.It is found that theξof x%Fe:BZ-0.96BT（x=0～2）ceramics change from～1.63μm to～1.23μm.x%Fe:BZ-0.96BT（x=0～0.8）ceramics have an O+T phase coexistence structure,x%Fe:BZ-0.96BT（x=1～2）ceramics have an O+C phase coexistence structure.At the composition of x=1 where the ceramic phase structure changes,theε_m、T_m、Curie temperature（T_C）、γ、E_c、P_m、P_r、d₃₃ and W_rec of x%Fe:BZ-0.96BT ceramics suddenly change.The frequency dispersion of x%Fe:BZ-0.96BT（x=0～0.8）ceramics near the O-T phase transition temperature(T_O-T)is similar to the relaxor behavior of a slush polar state.The O-T phase boundary can increase the W_rec of x%Fe:BZ-0.96BT（x=0～0.8）ceramics.