Electric Properties Study On The Ce、Co Doping Of Na_0.5Bi_4.5Ti₄O₁₅ Ceramics With High Curie Temperature

Bismuth perovskite ceramics with high Curie temperature,low dielectric loss and good piezoelectric ferroelectric properties have gradually become popular materials for scholars at home and abroad due to their environmental friendliness.In this paper,the Na_0.5Bi_4.5Ti₄O₁₅ceramics were chosen as the object to study.The A-site Ce doping and A/B-site co-doping with Ce and Co were made on it to explore the influence of doping on the crystal structure of ceramics.The influence of the crystal structure change and defect regulation on the polarization behavior,dielectric,piezoelelctric,ferroelectric performance of ceramics was also studied to get a kind of piezoelectric ceramics with enhanced electric properties and high Curie temperature,which broadens its range of application.Firstly,the crystal structure of the bismuth layer perovskite ceramics was studied and the influence of its special layered structure on its piezoelectric ferroelectric effect in the polarization behavior was investigated.We found that the c axis of the bismuth layered perovskite ceramic is too long to make the dipole difficult to flip,so the ceramic is difficult to be polarized.We chose GSAS software to refine the Rietveld structure of ceramics,and explore the influence of doping on the crystal structure of ceramics and the relationship between the change of crystal structure and electrical properties.The bismuth layered perovskite ceramics,Na_0.5Bi_4.5-xCe_xTi₄O₁₅（x=0,0.02,0.04,0.06,0.08,0.10）,were prepared by the traditional solid phase method.The phase analysis was made by X-ray diffraction,and the diffraction spectrum was fitted and calculated by Rietveld refinement to obtain the cell parameters.The microstructure of samples were observed and the electric properties were tested to investigate the influence of the change of ceramic crystal structure on the polarization behavior and its relationship with the electrical properties.The results show that the ceramics with x=0.04 has the best density.The piezoelectric properties increase firstly then drop with the increase of the Ce content and the maximum is got at x=0.04(d₃₃=20 p C/N),the change tendency of which is same as the b/a.After the doping,the dielectric loss of the ceramics decreases significantly,and it changes slowly in the low temperature region,which means the ceramics have wide working temperature range.With the increase of Ce,the Curie temperature decreases firstly then goes up and the minimum value is obtained at x=0.08,which is still higher than 600 ℃.Meanwhile,the remanent polarization of ceramics decreases first then increases with the increase of the doping amount,reaching the optimal value at x=0.08,which is opposite to the trend of the tetragonality index c/a.Na_0.5Bi_4.46Ce_0.04Ti_4-xCo_xO_y（x=0,0.01,0.02,0.03,0.04,0.05）ceramics were also fabricated via traditional solid phase method.The X-ray diffraction,dielectric and ferroelectric analysis were studied.The results proved that phase of the ceramics was pure and it belongs to the dielectric ceramics（E_a=0.91-1.39 eV）.The resistivity and activation energy decrease first then increase when the content of Co increases,and the minimum value is obtained when x=0.02.The dielectric constant and dielectric loss of the doped samples were reduced,and the Curie temperature was increased,reaching the maximum value at x=0.04（T_C=661.5 ℃）.At the same time,the remanent polarization of the ceramics increased then down,the maximum value was observed at x=0.02（2P_r=0.934μC/cm²）.