Structure And Electrical Properties Of BaTiO₃-BiScO₃-based Dielectric Ceramics

Barium titanate(BaTiO3)is a typical multi-purpose materials.It is widely used in many fields because of its excellent piezoelectric,ferroelectric,photoelectric,and high dielectric constant characteristics.It is very valuable ferroelectrics.In order to broaden the wide application of BaTiO3 in the energy-storage and high-temperature capacitors,BaTiO3-based Relaxor ferroelectrics(RFE)has become a new research highlight of dielectrics.However,the characteristics of various solid solutions have not been fully explored,recently.There is a BaTiO3-BiScO3(BT-BS)materials,it has temperature stablely and high energy storage.The structure and electrical properties of the solid solution were studied in this work based on the BT-BS system,which was modified by solid solution.The multi-phase BT-BS-based ceramics were synthesized by the solid phase method,and the structure,dielectric,impedance and ferroelectric properties of the ceramics were investigated.The main work is as follows:Firstly,in order to explore the effect of the B-site co-substituted ion recombination effect on the structure and properties of BT-BS materials,BaTiO3-Bi(Al0.5Sc0.5)O3 ceramics were designed and synthesized.The lead-free single-phase perovskite BaTiO3-Bi(Al0.5Sc0.5)O3 ceramics were synthesized by a solid-state reaction method.Effect of BAS content on the structure,dielectric properties,energy storage of(1-x)BT-xBAS ceramics were investigated.The long-range ferroelectric order of ceramics is destroyed by BAS.Also,the phase transition of BT-xBAS ceramics is from a typical ferroelectric phase to a relaxor phase,and the dielectric peak broadens with the BAS content increases,exhibiting a dispersive dielectric behavior with respect to frequency.The phenomena both indicate that the BT-BAS ceramics could have the excellent characteristics of relaxor ferroelectrics.The 0.85BT-0.15BAS ceramics show a good temperature stability,and the diffusion coefficient y is 1.97.There are an energy storage density of 0.684 J·cm-3 and an energy efficiency of 95%in an electric field of about 105 kV·cm-1.So as to understand the effect of structure on properties,starting from the first principles,based on density functional theory,the unit cell of BT-BAS was optimizedgeometrically.The density of state and energy band structure of the materials were calculated.It is believed that the A and B sites in the perovskite ferroelectrics has an important influence on the electrical properties of the materials.Secondly,for the purpose of meeting the industrial needs,to widen the working temperature range of BT-based materials,the research was started from 0.7BaTiO3-0.3BiScO3 solid solution.Pure 0.7BaTiO3-0.3BiScO3 was selected as the matrix,NaNbO3(NN)as the modifying member.A series of wide-temperature dielectric stable(1-x)(0.7BT-0.3BS)-xNN ceramics were successfully prepared by solid state reaction method.Effect of NN content on the structure,dielectric properties,energy storage and conductivity mechanism of the ceramics was investigated.The system ceramic is a p-type electronic conductivity mechanism dominated by grain boundaries.The compositions with NN content of 0.02 show excellent dielectric temperature stability with TCPppm is 0.0037 in the range of RT～200℃,dielectric constantεr150℃ of 786.8 and dielectric loss tan δ150℃ of 0.0019 at 1kHz,which is superior to many other temperature stable dielectric materials.Finally,in order to obtain high temperature dielectric ceramics,a perovskite phase BiFeO3 with a high Curie temperature was doped,0.05BiScO3-(0.95-x)BaTiO3-xBiFeO3 ceramics were synthesized by a solid-state reaction method.Effect of BF content on the structure,dielectric properties,impedance of the 0.05BS-BT-xBF ceramics was investigated.0.05BS-BT-xBF solid solutions possessed a pseudocubic structure,which is a typical relaxor ferroelectrics;and the conduction process is the small polarons jump mechanism.As BiFeO3 increased the grain size of the ceramics decreased and then increased.From the temperature dependence of dielectric constant,the 0.05BS-BT-0.08BF shows excellent dielectric properties:εm=15148.55,Tm=419.78Κ,and tanδ=0.350683 at RT.Therefore,the BF obviously increases the dielectric constant and Curie temperature of the ceramic(>370℃).It is indictated a potential application in high temperature.