Preparation And Dielectric Energy Storage Properties Of BaTiO₃-BiMeO₃ Composite Ceramics

With the energy crisis becoming more and more serious,people begin to devote themselves to the development of green energy and take the path of sustainable development.Therefore,countries are committed to the development of new energy technologies to make efficient use of existing energy and maximize benefits.As an important part of integrated circuit,dielectric capacitor has been extensively applied in filter,sensor,pulse capacitor and other fields,and also plays an irreplaceable role in communication,national defence,medical and other aspects.Due to its unique dielectric and ferroelectric performances.barium titanate（BT）,as a classical ferroelectric,is extensively used in application.Therefore,BT-based ceramics are selected as the main research materials in this paper.Through component control,BT can be induced from normal ferroelectrics to become relaxor ferroelectrics.Additionally,ions with different functions are introduced to enhance the polarization,breakdown field strength,relaxation behaviour of ceramics,and finally excellent dielectric and energy storage properties will be achieved.In addition,the high temperature dielectric relaxation of BT-based composite ceramics was systematically analysed to investigate its conduction mechanism.The specific research contents are as follows:Firstly,Sm doped 0.95Ba Ti O₃-0.05Bi(Mg_0.5Ti_0.5)O₃（BT-BMT-x Sm）lead-free ferroelectric ceramics were synthesised by high temperature solid-state method.The effects of Sm-doping on the microstructure,morphology,domain structure,dielectric and ferroelectric properties of BT-BMT ceramics were systematically analysed and studied.The results show that as the increase of doping content,the tetragonal phase changes to pseudo-cubic phase,the grain sizes grow up,and the hysteresis loop becomes thinner.The excellent energy storage density of 3.86 J/cm³ and efficiency of81.8%were obtained in BT-BMT-0.03Sm ceramics.Through the analysis of complex impedance and X-ray photoelectron spectroscopy,it can be found that the increase of breakdown field strength was related to the content of oxygen vacancies in the sample.Finally,the optimized samples were tested at different temperatures and frequencies,showing good frequency and temperature stability.Then,a series of（1-x）Ba Ti O₃-x Bi(Zn_0.5Hf_0.5)O₃（（1-x）BT-x BZH）ceramics were synthesized by two-step method.After introducing the addition BZH into BT ceramics,the phase structure and grain size of ceramics can be adjusted to obtain optimized ceramics with high breakdown field strength and relaxation characteristics.When x value is 0.12,the optimal energy storage ceramic is obtained and the excellent energy storage density is 3.62 J/cm³ and its corresponding efficiency is 88.5%.In addition,the ceramic shows good performance stability in the temperature range of 25～115°C and frequency range of 1～500 Hz.The charge-discharge measurement of 0.88BT-0.12BZH ceramics are carried out and it can be found that the discharge time,discharge density,current density and power density at 120 k V/cm are 100 ns,1.2 J/cm³,519.4 A/cm²,31.1 MW/cm³,respectively.Finally,the high temperature dielectric relaxation of（1-x）BT-x BZH（x=0.0,0.04,0.08,0.12）ceramics was studied.Through the analysis of complex impedance,it can be found that the dielectric relaxation may be related to the movement of oxygen vacancy.Comparing the relaxation activation energy with the conductance activation energy,it is found that the relaxation mechanism is mainly dipole conduction mechanism,while the conductance process in ceramics is mainly caused by the migration of double ionized oxygen vacancies.