The Study On Optial-bandgap And Electromagnetic Properties Of Bi_0.5Na_0.5TiO₃-based Ferroelectric Semiconductor Ceramics

Perovskite-oxide ferroelectric semiconductors were widely concerned in photovoltaic applications due to its excellent optical absorption and thermal stability.And it have potential applications in light sensors,thermal materials,solar cells and so on.In recent years,with the sustainable development of the environment,Bi_0.5Na_0.5Ti O₃ green lead-free materials have become the focus of research.However,there are few reports on semiconductor photovoltaic,the main reason is that pure Bi_0.5Na_0.5Ti O₃ materials have high band gap,which limits the development of semiconductor photovoltaic.Therefore,in order to solve this problem,Ag,Ba Nb_0.5Ni_0.5O₃ composite modified Ba_xBi_0.5-0.5xAg_0.05-0.5xNa_0.45Ti_1-xNi_0.5xNb_0.5xO₃?abbreviation as BANT-x BNN,x=0.00,0.02,0.04,0.06,0.08?semiconductor ceramics and ilmenite materials modified?1-x?Bi_0.5Na_0.5Ti O₃-x ATi O₃?abbreviation as?1-x?BNT-x ATO,x=0.02,0.04,0.06,0.08,0.10,A=Ni,Mn,Co?semiconductor ceramic were successfully prepared by solid-phase method.And the dielectric properties,ferroelectric properties,optical band gap and photovoltaic properties were systematically studied.The BANT-x BNN ceramics are fully made of perovskite structure without obvious secondary phase.When x>0.06,a split peak was observed in the high angle,which indicated that the structure of BANT-x BNN ceramics changed from rhombohedral phase to pseudo-cubic phases.All the BANT-x BNN ceramics illustrate perfect ferroelectric and magnetic properties as well as the characteristics of relaxor ferroelectrics.When x=0.06,the polarization and magnetization reach the maximum.The addition of Ba Ni_0.5Nb_0.5O₃ can substantially reduce the band gap of Ag doped Bi_0.5Na_0.5Ti O₃material to?2.3 e V.The short-circuit current(J_sc)and the open-circuit voltaic(V_oc)of the selected BANT-0.04BNN ceramic poled at 2.0 k V,is 2.79 n A/cm² and 0.54 V,respectively.All the NiTiO₃ modified?1-x?BNT-x NTO?x=0.02-0.10?semiconductor ceramics have good ferroelectric properties,and the maximum polarization at x=0.06.The diffuse factor?decreases slightly from 1.732 to 1.571 with the addition of Ni Ti O₃.In addition,Ni doping can substantially reduce the band gap of Bi_0.5Na_0.5Ti O₃materials to?2 e V.And the ceramics have good paramagnetic properties,and the maximum magnetization(M_max)is 25.21,30.54,38.39,49.03 and 57.97 memu/g,respectively.In a 0.94BNT-0.06NTO compound,the XPS spectra shows that he Ni ions is in+2 valence state,and the area ratio of Bi³⁺and Bi⁰⁺is approximately 4:5,and the area ratio of Ti⁴⁺and Ti³⁺is approximately 1:2.Moreover,the short-circuit current(J_sc)in the composition is 1.36 n A/cm²,and the open-circuit voltaic(V_oc)is 0.35 V for photovoltaic properties.The ferroelectric and photovoltaic properties were investigated for the Mn Ti O₃Modified?1-x?BNT-x MTO?x=0.02-0.10?semiconductor ceramics.All the ceramics have good ferroelectric properties,and the minimum polarization?P_m?,residual polarization?P_r?and lower coercive field?E_c?at x=0.06.The diffuse ferroelectrics of ceramics were confirmed from the dielectric temperature spectrum.At the same time,the ceramics have good paramagnetic properties,and the maximum magnetization(M_max)increases from 47.64memu/g to 110.06 memu/g with the addition of Mn Ti O₃.In Ag/0.94BNT-0.06MTO/ITO devices,ceramics show perfect photovoltaic properties.The short-circuit current(J_sc)and the open-circuit voltaic(V_oc)of poled ceramic is 1.72 n A/cm² and 0.26 V,respectively.The perovskite structure and good ferroelectric properties were observed for all the Co Ti O₃ modified?1-x?BNT-x CTO?x=0.02-0.10?semiconductor ceramics,and the minimum coercive field?E_c?at x=0.06.All the ceramics also have relaxor behavior and paramagnetism.The 0.94BNT-0.06CTO poled ceramics show perfect photovoltaic properties,and the J_scand V_oc is 1.00 n A/cm² and 0.13 V,respectively.Moreover,it can be seen from the complex impedance test that with the increase of temperature,the resistance of ceramics decreases gradually,the activation energy of the grains and grain boundaries are 0.48 and 0.52 e V respectively,and there is an interface effect between the ceramic surface and electrode.