The Energy Storage Properties And High-temperature Dielectric Relaxation Behaviors Of Off-stoichiometry Barium And Titanium Oxide Ceramics

Ferroelectric functional ceramics have excellent physical properties such as electricity,sound,heat,force,and light.Capacitors with ceramic bulk as the dielectric layer are universally adapted to the printed circuit board.How to achieve the high energy storage density of ceramic capacitors has grow into a hot topic of current study.The dielectric layer of the lead-based materials is now widely used in commercial applications.However,for environmental and body health considerations,the hunt for a lead-free base dielectric layer which involving high energy storage density has become an important branch.In view of the current demand for high energy storage density ceramics,the concept of environmental sustainability,and the practicality of ceramic capacitors,this article focuses on non-lead-based ceramic systems:improving the energy storage density of ceramic dielectrics from the perspective of defect gain;From the perspective of ceramic tolerance factor to adjust the crystal structure to improve the thermal stability of the dielectric.This method has practical operability and also provides a feasible way of thinking for material performance control.In this thesis,high-temperature solid-phase reactions were used to synthesize different types of ferroelectric ceramics using metal oxides and carbonates as raw materials.The main contents are as follows:（1）Based on BaSn_0.1Ti_0.9O₃,from the perspective of defect gain,a non-stoichiometric ratio of rare earth element lanthanum doped Ba_1-xLa_xTi_0.9Sn_0.1O₃（BLTS）ferroelectric ceramics was prepared.The electrical module properties,impedance properties,and dielectric properties of the modified ferroelectric ceramics were studied.Through the design of the non-stoichiometric ratio,when the doping content is 3 mol%structure,the maximum recoverable energy density(W_rec=4.44 J/cm~3)and the energy storage efficiency（η=91.49%）were collected.Through the dielectric properties,impedance spectrum,and the analysis of X-ray electron spectroscopy found that the improvement of the overall performance of ferroelectric spectroscopy shoud be attributed to the improvement of the overall assembly strengthen assisted by defect dipoles.（2）Zr⁴⁺doped Lanthanum Barium Titanate(Ba_0.955La_0.03Ti_1-yZr_yO₃,BLTZ)were prepared by high temperature solid state reaction method.The thermal stability properties,dielectric properties,impedance properties and energy storage properties of BLTZ were studied in this part.With the increasing of the content of Zr⁴⁺ions,the thermal stability of this system has been improved（from 15℃～75℃ to 15℃～85℃）.when y equals 0,0.015,0.03,0.045,separatly,the recoverable energy storage density is 1.38 J/cm~3,1.51 J/cm~3,1.62J/cm~3,1.40 J/cm~3,separatly;The calculation results of these ceramics show that the doping of Zr⁴⁺ions have little effect to the energy storage of BLTZ.Aformentioned results show that the adjusting of the Goldschmidt tolerance factor of ABX₃ perovskite crystal structure could improve the thermal stability of this materials.It also reflects the universal law:macro properties depend on the micro structure.The high temperature dielectric relaxation behavior of BLTZ is attributed to the jumping conduction of double ionized oxygen vacancies.（3）The lanthanum and barium titanate ferroelectric ceramics co-doped with zirconium ions and tin ions(Ba_0.955La_0.03Zr_0.02Ti_0.98-zSn_zO₃,BLZST)were prepared by high-temperature solid-phase reaction.This part studys the dielectric properties,ferroelectric properties,impedance properties,and so on.The Field emission scanning electron microscopy was used to observe the micro surfacr of ceramic.The observation results show a good compactness.With the gradual change of Sn/Ti ratio,the breakdown electric strengthen of this system increases firstly,and then drop down.The difference between Sn/Ti ratio makes the degree of lattice distortion inconsistent,which will further change the electrical properties of these ceramics.The test results of dielectric properties and impedance spectroscopy at high-temperature range show that the high-temperature dielectric relaxation behavior is associated to the migration of oxygen vacancies.