Design Preparation And Energy Storage Properties Of BaTiO₃ Based Ceramic

In recent years,the non-renewable nature of traditional fossil energy and the environmental pollution caused by it have received extensive attention from the international community.In order to slow down the depletion of fossil energy and avoid its harm to the environment.As the best alternative to fossil energy,the development and utilization of renewable green and clean energy such as wind,tidal and solar energy has attracted extensive research.Among them,the storage and conversion of renewable energy is the key link that can be applied in practice.Among the many energy storage devices,dielectric ceramic materials have attracted people’s research interest because of their unique advantages of ultra-fast charging and discharging speed and ultra-high power density.At present,most of the practical applications on the market are lead-based ceramic capacitors,and the volatility of lead elements during high-temperature processing is easy to cause harm to the surrounding environment and human health.Therefore,the preparation of lead-free ceramic capacitors with energy storage performance comparable to lead-based ceramic capacitors is a hot spot in current research.BaTiO₃（BT）-based ceramic materials have high dielectric constant,low dielectric loss and high spontaneous polarization.It is known as the pillar of the electronic ceramics industry,however,its low breakdown strength and high residual polarization limit its direct application in energy storage.In this project,a variety of strategies were used to adjust the various characteristics of BT ceramics,and the samples were analyzed by combining various characterization methods,aiming to comprehensively improve their energy storage performance.Ba1-xCaxTiO₃ lead-free energy storage ceramics were prepared by combining traditional solid-phase reaction method and cold isostatic pressing molding.The effects of Ca²⁺ doping on BT ceramic structure,micromorphology,dielectric,energy storage and other aspects were analyzed.The results show that when the Ca²⁺ doping content is less than 0.30,the tetragonal phase structure of the ceramic is continuously enhanced with the increase of the doping content,and Ca²⁺occupies the position of Ba²⁺.When the Ca²⁺ doping content is greater than 0.30,the tetragonal structure of the ceramic weakens,and the unit cell volume begins to expand.With the increase of Ca²⁺ doping content,the grain size of ceramic decreases,thereby effectively improving the breakdown strength of ceramics.It can be seen from the dielectric temperature spectrum that the doping of Ca²⁺ helps to improve the dielectric stability of BT ceramics,and the transition temperature of the tetragonal-cubic phase becomes stable.Ba_0.70Ca_0.30TiO₃（BCT）ceramics exhibited Wrec=0.804 J/cm3,η=72.7%energy storage performance under an electric field of 168 kV/cm.Compared to pure BT,its breakdown field strength is increased by 40%,Wrec is increased by 55%,and η is increased by 10%.（1-x）Ba_0.70Ca_0.30TiO_3-xNa0.5Bi0.5TiO₃ ceramics（（1-x）BCT-xNBT）were prepared by combining traditional solid-phase reaction method and cold isostatic pressing molding.After the introduction of NBT,ceramics all exhibited a single perovskite structure,the grain size of ceramics decreased,the dielectric loss and dielectric constant continued to decrease,and the frequency dispersion phenomenon of dielectric peak was obvious.At the same time,the addition of NBT destroys the long-range ordered structure of BCT ceramics and enhances the relaxation behavior of BCT ceramics.At x=0.30,0.70BCT-0.30NBT has the best energy storage characteristics:Wrec=1.95 J/cm³ under an electric field of 310 kV/cm,η=84.5%energy storage performance.0.70BCT-0.30NBT ceramics exhibit excellent temperature and frequency stability at an electric field of 150 kV/cm.（1-x）Ba_0.70Ca_0.30TiO_3-xK_0.5Na_0.5NbO₃ ceramics（（1-x）BCT-xKNN）were prepared by combining the traditional solid-phase reaction method and cold isostatic pressing molding.The results show that the addition of KNN causes the quadripartite-cubic phase transition of ceramics.With the increase of doping content,the average grain size and residual polarization continue to decrease,which effectively improves the breakdown characteristics of ceramics.The regulation of different valence states and ion radii disrupts the long-range order of BCT ceramics and enhances the relaxation characteristics of ceramics.0.85BCT0.15KNN ceramics obtained 2.36 J/cm³ under an electric field of 345 kV/cm,with a η of 90.1%.At the same time,0.85BCT-0.15KNN ceramics have a fast discharge time of 57.2 ns.