Preparation Of （1-x）（Ba,Li）TiO₃-xBiMeO₃ Ceramics And Their Energy Storage Properties

Dielectric energy storage ceramic capacitors are widely used in hybrid electric vehicles,medical laser,petroleum exploration and other fields due to their advantages such as high power density,fast charge and discharge rate,good temperature stability,and strong anti-aging property.The larger dielectric constant and higher polarization strength of Ba TiO₃（BT）ceramics are of great significance for the development of their energy storage properties.However,due to the defects of BT ceramics,such as high residual polarization strength,low breakdown field strength E_b,large dielectric loss tanδand poor dielectric stability,it is difficult for the ceramics to obtain superior energy storage performance.In this paper,Ba_1-xLi_xTiO₃ ceramics were obtained by doping Li₂CO₃ into BT ceramics.Bi（B’,B’’）O₃ was then introduced into Ba_1-xLi_xTiO₃ matrix to fabricate（1-x）Ba_1-xLi_xTiO₃-x Bi（B’,B’’）O₃relaxation ferroelectric ceramics(where B’,B’’=Y³⁺,Al³⁺;B’=Mg²⁺;B’’=Sn⁴⁺,Nb⁵⁺).The generation of polar nanoregions（PNRs）in relaxor ferroelectrics is used to reduce the coercient field and residual polarization intensity.At the same time,the dispersive phase change behavior of relaxor ferroelectric material is used to improve the temperature stability of the material,and then the good energy storage performance is obtained.The main research contents are as follows:（1）The（1-x）Ba_0.98Li_0.02TiO₃-xBi(Mg_1/2Sn_1/2)O₃ceramic samples were prepared by solid-phase sintering at 1250℃for 2 hours.The X-ray diffraction pattern showed that the ceramic samples of all components were single perovskite structure and basically had no impurity phase.Phase transition occurs near x=0.05,and the ceramics change from tetragonal symmetry to cubic symmetry.Tetragonal phase and orthogonal phase coexist when x≤0.05,then the coexistence of cubic phase and orthogonal phase was found in the comsition with x>0.05.The diffraction peak shifted to smaller angle with the increase of the doping content,which corresponded to the increase of the cell volume.The uniform grain distribution,clear grain boundary and low porosity of the ceremics are beneficial to increase the breakdown field strength.The highest relaxation degree withγvalue of 1.792 was obtained at x=0.06.The optimal energy storage density 0.159 J/cm³was obtained under the maximum breakdown field intensity of 65 k V/cm,and the optimal energy storage efficiency was 73.23%.（2）（1-x）Ba_0.98Li_0.02TiO₃-xBiYO₃ ceramic samples were prepared by solid-phase sintering at 1250℃for 2 hours.According to XRD,all the ceramic samples are of single perovskite structure with no impurity phase,indicating that Bi³⁺and Y³⁺enter the BLT lattice forming a complete solid solution.Phase transition occurs near x=0.06.Based on Winplotr fitting diagram and Raman diagram,tetragonal phase and orthogonal phase coexist in the composition with x≤0.06,while cubic phase and orthogonal coexist at x>0.06.The diffraction peak shifted to smaller angle with the increase of the doping content,indicating the increase of cell volume.The compositon with x=0.06 reached to the highest relaxation degree withγvalue of 1.98.The maximum breakdown field strength of（1-x）Ba_0.98Li_0.02TiO₃-xBiYO₃ ceramics was 65 k V/cm,the maximum energy storage density was 0.289 J/cm³,and the optimal energy storage efficiency was 80.05%.（3）（1-x）Ba_0.98Li_0.02TiO₃-xBiAlO₃ceramic samples were prepared by solid-phase sintering at 1250℃for 2 hours.According to XRD analysis,the ceramics of each component formed single-phase solid solution.The ceramics change from tetragonal symmetry to cubic symmetry near x=0.05.The diffraction peak shifted to smaller angle with the increase of x,corresponding to the increase of cell volume.SEM images showed that the grain size decreases with x increasing due to the low melting point ofBiand the formation of liquid phase in the sintering process.For（1-x）Ba_0.98Li_0.02TiO₃-xBiAlO₃series ceramics,The maximum breakdown field strength of 60k V/cm was obtained at the compostition with x=0.10,the maximum energy storage density and the optimal energy storage efficiency are 0.22 J/cm³ and 60.36%,respectively.（4）The（1-x）Ba_0.96Li_0.04TiO₃-xBi(Mg_2/3Sn_1/3)O₃ ceramic samples were prepared by solid-phase sintering at 1150℃for 2 hours.The XRD analysis showed that all the ceramic samples were single perovskite structure,indicating that Bi³⁺and(Mg_2/3Nb_1/3)³⁺entered the BLT lattice to form a complete solid solution.Phase transition occurred at the compostition with x=0.04～0.06.The diffraction peak shifted to smaller angle with the increase of x amount,indicating the increase of cell volume.The dielectric peak diffused and widen greatly at x>0.06,the dielectric ceramics transformed into relaxor ferroelectric.The optimal energy storage density 0.2938 J/cm³was obtained under the maximum breakdown field intensity of 72.5k V/cm,and the optimal energy storage efficiency is 85.34%.