Microstructure Regulation And Texture Enhancement Of Barium Zirconate Titanate-based Lead-free Piezoelectric Ceramics On Electrical Properties

With the enhancement of people's environmental awareness and the limitation of relevant laws and regulations,the research and development of high-performance lead-free piezoelectric ceramics to replace the traditional lead-based piezoelectric ceramics has become a key problem to be solved.Among many lead-free piezoelectric ceramic research systems,barium calcium zirconate titanate(BCZT)based piezoelectric ceramics have attracted the attention of researchers because of its excellent dielectric properties,simple preparation and no pollution.In order to solve the problems of high sintering temperature(>1450?)and unbalanced comprehensive electrical properties of BCZT based piezoelectric ceramics,it is proposed for the first time to combine microwave sintering with texture chemical technology to construct a rhombohedral-orthogonal-tetragonal(R-O-T)multiphase coexistence to enhance the comprehensive electrical properties of BCZT based piezoelectric ceramics.This paper mainly carries out the research work from the following aspects:(1)BCZT lead-free piezoelectric ceramics with pure perovskite structure were obtained by microwave sintering at 1275?for 2 h.The average grain size of the ceramics was 8.37?m,and the optimal electrical properties were as follows:d₃₃=418 p C/N,P_r=12.39?C/cm²,E_C=0.36k V/cm,T_C=101?,?_r=5512.Compared with the traditional solid-state sintering process,the comprehensive electrical properties of microwave sintering samples are better than the traditional solid-state sintering samples,and the microwave sintering temperature is lower.The results show that microwave sintering can make the ceramic grains grow rapidly and uniformly,and obtain larger grain size,which is conducive to the domain deflection.The two-phase coexistence(O-T)is formed in the crystal phase,which reduces the potential barrier of free polarization deflection and promotes the domain deflection,thus improving the comprehensive electrical properties of BCZT ceramics.(2)SrTiO₃(ST)crystals with cubic structure were prepared by two-step molten salt method.BCZT-10 wt.%ST lead-free piezoelectric ceramics were successfully prepared by microwave sintering at 1300?for 1 h.The three-phase coexistence of R-O-T can be obtained in the grains.The optimal electrical properties are as follows:d₃₃=447 p C/N,?=4.97g/cm³,T_C=82?,?_r=7791,tan?=4.80%,P_r=3.90?C/cm²,E_C=3.43k V/cm.In addition,ST can act as a template to guide the texture growth of BCZT along the<001>direction,but the texture degree of BCZT-ST ceramics is only 29%.(3)Based on the principle of topological chemical in-situ growth of Aurivillius structured oxides,pure perovskite structure and uniform sheet SrTiO₃(ST)and Ba Ti O₃(BT)template grains were prepared by three-step molten salt method,respectively.The width thickness ratio of ST template is about 4:1,with an average size of 2.02?m;the width thickness ratio of BT template is about 5:1?13:1,with an average size of 2.63?m.(4)BCZT-ST ceramic films doped with 2.0 wt.%,4.0 wt.%,6.0 wt.%,8.0 wt.%ST templates and BCZT-BT ceramic films doped with 1.5 wt.%,3.0 wt.%,4.5 wt.%,6.0 wt.%BT templates with different thicknesses were prepared by tape casting process,respectively.By testing the texture of the two kinds of ceramic films,the optimal thickness of tape casting film was determined to be 50?m.When the amount of ST template is 2.0 wt.%,the texture of BCZT reaches 86.8%after sintering at 1300?for 1 h,and the coexistence of R-O-T phases appears in the grain,which can significantly improve the comprehensive piezoelectric properties(d₃₃=503 p C/N,k_p=0.53,T_C=95?,?_r=16286,tan?=3.94%,P_r=9.57?C/cm²,E_C=1.74k V/cm).When the amount of BT template is 3.0 wt.%,the texture degree of BCZT-BT system reaches 97.9%after sintering at 1275?for 1.5 h,and the morphotropic phase boundary is also formed in the ceramics.The best electrical properties are as follows:d₃₃=575 pc/N,k_p=0.61,T_C=89?,?_r=15938,tan?=4.18%,Pr=10.91?C/cm²,E_C=2.20 k V/cm.BCZT-ST and BCZT-BT piezoelectric ceramics with high texture in<001>direction were successfully prepared by tape casting and microwave sintering.(5)Taking BCZT-BT system as an example,the mechanism of ceramic texture growth was expounded.In the process of preferred growth of ceramic grains along the<001>direction,the synergistic effect of microwave sintering and texturing can form 4R,4O and 1T engineering domain structures in the grains,which improves the activity of domain deflection in the ceramics,thus greatly improving the overall electrical properties of BCZT-BT ceramics.