Study On Structure Control And Piezoelectric Properties Of Na_0.5Bi_4.5Ti₄O₁₅ Bismuth Layered Ceramics With High Temperature Stability

Bismuth layered lead-free piezoelectric ceramics have received more and more attention due to their good high temperature stability and certain piezoelectric properties.They are very good in high temperature and harsh environments such as oil well exploration,aerospace,and nuclear power generation.Application prospects.In this paper,a representative 4-layer bismuth layered piezoelectric ceramic Na_0.5Bi_4.5Ti₄O₁₅was selected as the research object,and（1-x）Na_0.5Bi_4.3Er_0.2Ti₄O₁₅-x K_0.5Na_0.5Nb O₃was prepared by solid-phase reaction method.（x=0,0.05,0.1,0.15,0.2）ceramics and Na_0.5Bi_4.46Ce_0.04Ti_4-xCo_xO_y（x=0,0.01,0.02,0.03,0.04,0.05）ceramics,combined with Rieteveld structure refinement,systematically The change law between its structure and performance was studied.The main research contents are as follows:First,the crystal structure of bismuth layered ceramics is studied,and the effects of its unit cell parameters,unit cell volume and atomic bond length on its properties are explored.In this paper,the structure refinement software GSAS is used to perform Rietveld full-spectrum fitting on Na_0.5Bi_4.5Ti₄O_15-based ceramics,obtain crystal structure parameters,and explore the influence of doping on the ceramic crystal structure and the relationship between internal microstructure changes and external properties.Secondly,the high-voltage electroactive perovskite structure K_0.5Na_0.5Nb O₃was introduced into the NBT-based ceramics doped with quantitative Er at the A site,and（1-x）Na_0.5Bi_4.3Er_0.2Ti₄O₁₅-x K_0.5Na_0.5Nb O₃（x=0,0.05,0.1,0.15,0.2）ceramics was prepared by the solid-phase reaction method.XRD diffraction spectrum showed that the introduction of K_0.5Na_0.5Nb O₃did not change the single layered bismuth structure of Na_0.5Bi_4.5Ti₄O₁₅.Subsequently,the diffraction data was fitted with Rietveld full spectrum to obtain the crystal structure parameters of the sample,and to explore the influence of the introduction of K_0.5Na_0.5Nb O₃on the structure of Na_0.5Bi_4.5Ti₄O₁₅and its relationship with electrical properties.The experimental results found that the sample lattice distortion index b/a decreases with the increase of K_0.5Na_0.5Nb O₃content,which leads to an increase in the symmetry of the crystal structure,and at the same time the impedance value of the sample decreases,and it is easy to break down during polarization.The ferroelectric performance is reduced,and the piezoelectric performance is not improved much.In addition,the dielectric temperature spectrum shows that an appropriate amount of K_0.5Na_0.5Nb O₃content can effectively reduce the dielectric loss of the sample（x=0.1,tanδ=0.00447）,and improve the thermal stability of the dielectric properties of NBT ceramics.Finally,prepared Na_0.5Bi_4.46Ce_0.04Ti_4-xCo_xO_y（x=0,0.01,0.02,0.03,0.04,0.05）ceramics doped with quantitative Ce at the A site and Co changed at the B site,and systematically studied the total of Ce and Co The influence of doping on its microstructure and electrical properties.The experimental results show that all ceramic samples have a single Na_0.5Bi_4.5Ti₄O₁₅phase structure.With the increase of x,the unit cell parameters,unit cell volume,B-O bond length and B-O octahedral volume of the samples decrease.The study found that after Co³⁺replaces Ti⁴⁺,defective dipole pairs are formed,which promotes the polarization effect and improves its ferroelectric properties.When x=0.2,the overall performance is the best,the grain size is moderate and uniform,the piezoelectric coefficient d₃₃=22p C/N,the residual polarization 2P_r=2.97（?）C/cm²,and the Curie temperature Tc=686℃,the smallest medium Electric loss tanδ=0.00582,which has high application potential.