Multielement Doping And Solid Solution Modification Of Sodium Bismuth Titanate-based Ceramics

Sodium bismuth titanate?NBT?has attracted much attention because of its high Curie temperature,good electromechanical coupling coefficient and excellent ferroelectric and piezoelectric performance.In addition,it is found that the material also has potential ionic conductive characteristics.The exploration of this performance impassion a new round of exploration.As the application of ferroelectric piezoelectric materials,the coercive field is difficult to be polarized,high leakage current and the performance is still needed to be improved.As the electrolytes,the conductivity of the material is to be further increased.In this paper,the sodium bismuth titanate material is modified by ion doping and solid solution formation to improve the properties referring to different use.The microstructure and electrical properties of the ceramic samples are investigated.Based on the principle of ion doping,Na_0.5Bi_0.5-xSr_xTi_1-xGa_xO_3-? ceramics were prepared by using the improved solid state reaction technique.Effects of Sr²⁺ and Ga³⁺ co-doping on the crystal structure,microstructure,impedance characteristics and dielectric properties of NBT ceramics were studied by X-ray diffraction,scanning electron microscope and electrical performance testing system.The conductivity of these materials is calculated.The results show that the conductivity of NBT ceramics are improved after the introduction of a certain amount of Sr²⁺ and Ga³⁺,where the grain conductivity and grain boundary conductivity can be clearly distinguished.With the increase of Sr²⁺ and Ga³⁺,the total conductance,grain conductivity and grain boundary conductivity increase first and then decrease.When x=0.03,the total conductivity is as high as 0.024 S/cm at 810 ? and the conductivity activation energy is reduced to 0.48 eV,indicating the potential use as solid electrolytes.The?1-x?Na_0.5Bi_0.5TiO_3-xLa(Zn_0.5Ti_0.5)O₃ solid solutions were fabricated via solid solution modification method.The phase structure,microstructure and dielectric property of the ceramics were investigated.The results indicate that the materials remain single perovskite structure after adding a certain amount of La(Zn_0.5Ti_0.5)O₃.The introduction of La(Zn_0.5Ti_0.5)O₃ displays a role in the refinement of grain,and the grain edge is more distinct and has a significant effect on the dielectric properties of the materials.The dielectric diffusion factor increases,relaxation enhances and the activation energy of dielectric relaxation decreases as increasing the content of La(Zn_0.5Ti_0.5)O₃.The activation energy of dielectric relaxation decreases to 1.32 eV at x=0.018.In addition,the introduction of La(Zn_0.5Ti_0.5)O₃ also improved the ferroelectric properties of the material system.With the increase of the amount of La(Zn_0.5Ti_0.5)O₃,the coercive field declined from 43.4kV/cm to 23.7 kV/cm.To enhance the ferroelectric properties of NBT-based materials,0.06BaTiO₃ was introduced on the basis of x=0.003 and x=0.018 to construct MPB of NBT.It is found that,the phase transition induced by the electric field is reversible phase transition when x=0.018 and irreversible phase transition at x=0.003.The dynamic piezoelectric constant d33*is increased to 680 pm/V.?1-x?Na_0.5Bi_0.5TiO_3-xLaGaO₃ ceramics were prepared by introducing LaGaO₃ component into sodium bismuth titanate system.It exhibits R3c phase as the slight addition of LaGaO₃.The ionic conductive characteristics are not observed as the addition of LaGaO₃.With the increase of LaGaO₃,the conductivity activation energy and the activation energy of dielectric relaxation of the material system decrease.At x=0.012,the conductivity activation energy is 1.30 eV,the activation energy of dielectric relaxation is 0.65 eV.And the conductivity activation mechanism and dielectric activation mechanism were studied,indicating that the material in the middle temperature of the ion conduction is mainly carried out by tunneling mechanism,making it expected as the medium temperature solid electrolytes.