Preparation,electrical And Photoelectrical Properties Of Bismuth-containing And Lead-free Ferroelectric Ceramics

Due to its simple and economical preparation process and various performance,ferroelectric ceramics have great application potential,such as sensors,photodetectors,etc.The structure of common ferroelectric ceramics is generally perovskite,such as BNT and its solid solution,as well as bismuth-containing layered compounds.In this paper,we select CaBi2Nb2O9 ceramics with bismuth layered structure,Bi0.5Na0.5TiO3 perovskite structure and(0.935-x)Bi0.5Na0.5TiO3-0.065BaTiO3-xSrTiO3 ceramics,containing bismuth elements and explore the light transmittance,dielectric,ferroelectric and photoelectric properties of the ceramics.In the first part,the bent CaBi2+xNb2O9+2x ceramics(x=0,0.01,0.02)were prepared by bismuth element self-doping and certain process.The transmittance results show that the CaBi2.02Nb2O9.06 ceramics obtain high transparency.The ferroelectric test results show that the ferroelectric performance is improved and the strain curve gradually tends to"butterfly shape" with the increase of bismuth,which is due to the reduction of vacancy carrier concentration by bismuth doping.In addition,about 9.8 pC/N was obtained in the CaBi2.02Nb2O9.06 ceramics.Combining with the dielectric temperature test,it can be seen that appropriate excess of Bi2O3 can improve the problem of large pores in ceramics.In the second part,nitrogen doped Bi0.5Na0.5TiO3 ceramics were prepared by nitrogen doping,which can reduce defects and replace oxygen positions.The methods like XRD,Raman and XPS show that nitrogen ions not only replace oxygen,but also make up the defect.The results of ferroelectric test show that the ferroelectric polarization of N-400 ceramics with thickness of 0.2 mm is enhanced and the distribution of nitrogen content in N-400 ceramics is relatively uniform.The light absorption shows that the bandgap of the nitrogen-doped samples decreases,especially the band gap of N-500 ceramics is only 0.7 eV.The photoelectric performance results show that the short circuit current of N-400 ceramics increases obviously after polarization,which is due to its excellent ferroelectric polarization.Based on the results of the second part,the third one is the preparation of N-doped(0.935-x)Bi0.5Na0.5TiO3-0.065BaTiO3-xSrTiO3 ceramics.The light absorption results show that the bandgap of the doped sample is indeed reduced.When ensuring that the coercivity field is unchanged,the ferroelectric results show that both the residual polarization strength and strain strength of the doped sample are improved,especially obtaining a large strain of about 2%in the sample of 0.933BNT-0.065BT-0.02ST.