Study On Electrical Properties Of Bismuth Layered Na_0.5Bi_4.46Ce_0.04Ti₄O_15+y Ceramics With High Curie Point

Bismuth layered lead-free piezoelectric ceramics have attracted the attention and research of many scientific researchers due to their unique electrical properties and structure.They have broad application prospects under high temperature and harsh conditions such as deep sea exploration,military industry,and nuclear energy.In this paper,Na_0.5Bi_4.5Ti₄O₁₅ with high Curie temperature(>600?)is selected as the research object.By doping the material with A/B site K₂CO₃?Ce O₂?Nb₂O₅,and the structure and performance of the material are explored by combining the structure refinement.The main research contents are as follows:First,Na_0.5Bi_4.5Ti₄O₁₅ for A site potassium doping,and the polarization effect of the material on the ceramic was studied.Preparation of K_xNa_0.5-xBi_4.5Ti₄O₁₅(x=0,0.04,0.08,0.12,0.16,0.20)ceramics using solid phase reaction method.After the phase,the influence of doping on the electrical properties of the sample sintered at 1080?was systematically analyzed.It is found that with the increase of potassium doping,the grain size of the sample gradually decreases,and the dielectric constant first increases and then decreases.When the potassium doping is x=0.16,the maximum dielectric constant is 1172.7,and the dielectric loss is the same.Compared with the non-doped state,the decrease in different degrees indicates that the doping of potassium helps to improve the dielectric properties of the material.With the increase of potassium doping,the piezoelectric and ferroelectric properties of the material are also improved in different ranges.When x=0.16,the maximum piezoelectric coefficient of 16p C/N,the maximum saturated polarization intensity of 2.10(?)C/cm² and the maximum residual polarization are obtained.The intensity value is 0.78(?)C/cm².It shows that potassium doping can improve the piezoelectric and ferroelectric properties of the material in different ranges.Secondly,Na_0.5Bi_4.5Ti₄O₁₅ was doped with cerium and variable potassium at the A site to study the polarization effect of the material on ceramics.The solid-phase reaction method is use to prepare K_xNa_0.5-xBi_4.46Ce_0.04Ti₄O_15+y(x=0,0.04,0.08,0.12,0.16,0.20)ceramics.On the basis of ensuring that the prepared material is single-phase,the material was sintered at 1060°C,and the relationship between its doping and electrical properties and structure was studied.It is found that the grain size decreases first and then increases with the increase of potassium doping.When the doping amount x=0.12,the material achieves the maximum piezoelectric coefficient d₃₃=23p C/N and the remanent polarization 2P_r=4.14?C./cm².It is attributed to the fact that potassium replaces bismuth and forms a defect dipole pair with a surrounding oxygen vacancy,which makes the polarization behavior easier and makes a positive contribution to the piezoelectric performance.The structure refinement Rietveld is used to analyze the material cell parameters and the structural distortion characteristic parameter b/a,and it is found that when the potassium doping is x=0.12,the distortion degree is the most severe.Analysis of the dielectric properties of the material found that with the increase of potassium doping,the size of the dielectric constant increased to varying degrees,and the peaks showed a tendency to move first to the right and then to the left.The polarization resistance of the sample decreases with increasing temperature.At the same temperature,potassium doping causes the polarization resistance of the sample to increase first and then decrease.When the temperature is 700?and the potassium doping is x=0.12,the polarization resistance Rp=18.934k?·cm is the maximum,and the maximum activation energy E_a=1.677e V is obtained.Finally,based on the previous experiment,the material is doped with B-site variable niobium to control the degree of material distortion.Use traditional solid-phase reaction method to prepare K_0.12Na_0.38Bi_4.46Ce_0.04Ti₄O_15+y+xwt%Nb₂O₅(x=0.05,0.1,0.15,0.2)material.On the basis of ensuring that the prepared material is single-phase,the material was sintered at 1040?,and the relationship between its doping and electrical properties and structure was studied.It is found that the ceramic grain size gradually increases with the increase of Nb doping,which is mainly due to a large number of oxygen vacancies.The analysis of the dielectric properties of the material found that as the doping of niobium element increases,the Curie temperature first increases and then decreases.When the doping amount of Nb is x=0.15wt%,the maximum Curie temperature of 675.2 appears.?.The dielectric constant decreases with the increase of Nb doping,which may be due to the decrease of spontaneous polarization due to the appearance of a large number of oxygen vacancies.When the doping amount of Nb⁵⁺is x=0.20wt%,the maximum activation energy E_a=1.455e V,and the maximum piezoelectric coefficient 19p C/N and the residual polarization intensity 2P_r=5.59(?)C/cm²,this is mainly due to the increase in the degree of Ti-O octahedral distortion in the material by the doping of Nb,which improves the electrical properties of the material.