Preparation And Energy Storage Properties Of（Ba,Li）TiO₃ Based Ceramics

Dielectric capacitors are widely used in pulse weapons,medical equipment,mobile electric equipment due to their large power density.Dielectric Ceramics are considered to be the optimum material for preparing high temperature resistant pulse capacitor,due to small size,long service life,fast charge-discharge speed,high mechanical strength,high energy-storage density.Ba Ti O₃expresses good ferroelectric and piezoelectric properties,and environmentally friendly features.However,Ba Ti O₃has several disadvantages such as poor temperature stability,low breakdown field strength,low energy storage density and energy storage efficiency.Therefore,modification of Ba Ti O₃is needed to promote the research and development of its energy storage performance.In this paper,Li⁺ions were introduced to charge the spatial arrangement of Ba Ti O₃crystal structure,then improve its breakdown field strength and energy storage density.The microstructure and energy storage performance are analyzed.Based on the（Ba,Li）Ti O₃ceramics with dense structure and good energy storage performance,the influence of rare earth elements on the energy storage performance of the（Ba,Li）Ti O₃ceramics was systematically studied,specific research contents are as follows:（1）In this paper,（Ba,Li）TiO₃ceramics were fabricated by the conventional solid-state sintering method at 1200℃for 2 h.The effects of Li⁺ions on the sintering process,microstructure and electrical are also studied.The experimental results indicate that Li⁺ions doping can greatly decreases the sintering temperature of（Ba,Li）Ti O₃ceramics from 1450℃to 1200℃.XRD patterns indicates,that all samples express pure tetragonal perovskite phase.SEM results show that Li⁺ions doping can efficiently inhibit the grain growth,with the average grain size deceasing from 1.03μm to 0.91μm.The doping of Li⁺improves the dielectric properties of（Ba,Li）Ti O₃ceramics,which transfers from ferroelectric to relaxor ceramics.It is worth noting that the Curie temperature of（Ba,Li）Ti O₃ceramics increases from 120℃to 130℃.The optimum energy-storage properties(W_rec=0.293 J/cm³)were obtained at x=0.04with energy storage density of 0.293 J/cm³and energy storage efficiency.The BDS increases from 39.2 k V/cm at x=0.01 to 77.5 k V/cm at x=0.04.The impedance analysis proves that electrons dominant the conductive process of（Ba,Li）Ti O₃ceramics.（2）(Ba_0.96Li_0.04)TiO₃-xmol%La（x=0-0.09）lead-free ceramics with doping concentration from 0 to 0.09 were fabricated by conventional solid-state sintering method at 1200℃for 2 h.The effects of La doping on the microstructure and electric properties were investigated.All the ceramics present pure tetragonal perovskite structure.Uniform and dense microstructures with average grain sizes were obtained and the grain size decreases from 1.41μm to 0.82μm.The polarization behavior and relaxor transition behavior were improved by donor doping of La.The dielectric breakdown strength（BDS）was greatly improved,and the value of the difference between maximum polarization(P_max)and remnant polarization（P_r）increases from13.76μC/cm²to 16.73μC/cm².The maximum recoverable energy storage density(W_rec)of 0.548 J/cm³was achieved for the 0.05 La-doped ceramics due to the improvement of BDS and the slimmer polarization-electric field hysteresis loop.（3）The lead-free energy storage ceramics of(Ba_0.96Li_0.04)Ti O₃-0.05mol%x（x=Sm、Yb、Gd、Er、Ce、La）were manufactured by conventional solid-state sintering method at the temperature of 1180℃-1200℃for 2 h.The effects of different rare earth element on the microstructure and electric properties of(Ba_0.96Li_0.04)Ti O₃were investigated.All the samples present pure tetragonal perovskite structure.The(Ba_0.96Li_0.04)Ti O₃ceramics doped by rare earth element with dense microstructures and uniform grain size,the rare earth element of Sm、Yb、Gd、Er、Ce、La can effectively inhabit grain growth with the grain sizes of 0.84μm、0.79μm、0.8μm、0.77μm、0.94μm、0.82μm,respectively.The maximum polarization of the ceramics can be improved by breaking down the A-O coupling at the Ba site.The energy storage density and energy storage efficiency are greatly improved by rare earth doping.Among this six elements,the optimum energy storage property was obtained by Yb with storage density of 0.275 J/cm³and energy storage efficiency of 67.3%at 60 k V/cm.