Effect Of (Bi_0.45Y_0.05)Na_0.5（Zr,M）O₃-Doped KNN-Based Lead-Free Piezoelectric Ceramics On Their Electrical Properties And Structure

Modern materials are essential to a country’s industry,and piezoelectric materials are critical to many cornerstones.Currently,the vast majority of the market in the field of piezoelectric actuators is dominated by PZT materials.Still,it can cause a large amount of pollution throughout its entire life cycle,which violates people’s environmental awareness and some laws restricting the use of lead.However,KNN lead-free piezoelectric ceramics have been extensively studied due to their excellent basic properties and huge development potential.In the traditional preparation process,KNN-based piezoelectric ceramics are challenging to prepare ceramics with good performance due to their poor deliquescence and sintering stability.To address these issues,this paper aims to improve the performance and structure of KNN-based piezoelectric ceramics doped with(Bi_0.45Y_0.05)Na_0.5（Zr,M）O₃ after A/B modification.Through research,it is found that KNN-based piezoelectric ceramics have an excellent physical structure.Their properties are significantly improved when there is a polycrystalline phase boundary（PPB）and the system is dense.To construct PPB,it is necessary to reduce the phase transition temperature of ceramics,while lush ceramic designs need to be obtained by improving their sintering process.With this goal in mind,we conducted the following research:In this paper,piezoelectric ceramic samples are all fired using the traditional solid-state method with good universality.Firstly,we introduced rare earth element Y³⁺intoBi_0.5Na_0.5ZrO₃,designedandprepared（1-x）(K_0.5Na_0.5)NbO₃-x(Bi_0.45Y_0.05)Na_0.5ZrO₃（KNN-BYNZ）lead-free piezoelectric ceramics,and studied the effect of BYNZ doping on the electrical properties and structure of KNN-based piezoelectric ceramics.KNN-BYNZ was a single perovskite structure,and the orthorhombic tetragonal phase’s phase transition temperature(T_O-T)was successfully lowered to near room temperature.PPB at room temperature was successfully constructed,and the sintering process of the ceramics was improved.The density significantly increased,and the grain size was uniformly distributed.By adjusting the value of x,it was found that the optimal performance was achieved at x=0.04:d₃₃=305p C/N,T_c=332℃,P_r=28.2μC/cm².Compared with pure KNN piezoelectric ceramics,the commission has been significantly improved.Based on previous research,the transition metal Mn partially replaced the Zr element at the B position of(Bi_0.45Y_0.05)Na_0.5ZrO₃.KNN based ceramics doped with(Bi_0.45Y_0.05)Na_0.5(Zr_0.85,Mn_0.15)O₃ were designed and prepared,including（1-x）(K_0.5Na_0.5)NbO₃-x(Bi_0.45Y_0.05)Na_0.5(Zr_0.85Mn_0.15)O₃（KNN-BYNZM）.The effects of BYNZM doping amount and Mn element on the structural and electrical properties of KNN-based ceramics were investigated;the relaxation phenomenon of KNN-BYNZM piezoelectric ceramics was preliminarily investigated.By adjusting the doping amount,the optimal performance was obtained at d₃₃=346p C/N,T_c=338.2℃,P_r=25.5μC/cm²,further improving the performance of KNN-BYNZ ceramics.It was found that the doping of BYNZM has an excellent softening effect,making it easier to construct PPB and the inversion of electrical domains.Mn also acts as a partial sintering aid,reducing the sintering temperature,improving the sintering performance of the ceramics,and further improving their performance.It was also found that the ceramics have a significant diffusion phase transition phenomenon,and the reason for its formation was briefly discussed.Finally,based on the previous and group studies,（1-x）(K_0.5Na_0.5)NbO₃-x(Bi_0.45Y_0.05)Na_0.5(Zr_0.85Sn_0.15)O₃（KNN-BYNZS）doped KNN-based piezoelectric ceramics were designed and prepared using zirconates containingSnelementsintheB-site:（1-x）(K_0.5Na_0.5)NbO₃-x(Bi_0.45Y_0.05)Na_0.5(Zr_0.85Sn_0.15)O₃（KNN-BYNZS）piezoelectric ceramics,the relationship between the amount of BYNZS doping and the electrical properties and structure of KNN-based piezoelectric ceramics were investigated.It was found that the doping of BYNZS effectively lowered the sintering temperature,reduced the volatilization of alkali metal elements in KNN-based piezoelectric ceramics,promoted the generation of the liquid phase,improved the sintering process,and made the structure denser.It was also found that diffusive phase transition also exists in ceramics.By changing the doping amount of BYNZS,the best performance of KNN-based ceramics was achieved at x=0.04:d₃₃=341p C/N,T_c=340℃,P_r=26.2μC/cm²,which improved the performance again based on the previous research of our group.