Design Of Composite Ceramics And Study On Energy Storage Properties Of PLZST-based Antiferroelectric Ceramics

In modern electrical and electronic systems,dielectric capacitors are ubiquitous for its high power density,high operating voltage and long service life,such as laser weapons,particle beam weapons,electromagnetic launchers,all-electric integrated warships and other military fields,and surface modification and cleaning,particle beam cutting and welding,petroleum exploration,hybrid vehicles and other industrial and civil fields.Dielectric materials,which can store electrostatic energy,are the key part in the capacitors.Antiferroelectric（AFE）materials are good candidates because of their double polarization-electric field（P-E）hysteresis loops characterized by a high polarization（P）,a small remnant polarization（P_r）and an electric field induced AFE to FE phase transition.However,because of the temperature induced phase transition,the polarization of most reported PLZST systems is seriously affected by temperature.The existing results show that it is difficult to obtain wide operating temperature rang and high temperature stability in AFE ceramics,which cannot meet the requirements of high temperature and high reliability.In addition,the hysteresis loss caused by the phase transition between AFE and ferroelectric（FE）phases will also reduce the energy storage efficiency.The energy loss is not only a waste of energy but may also cause the overheating of the devices.Therefore,it is of great significance and application value to improve the temperature stability and energy storage efficiency of AFE materials.In this study,the（Pb,La）（Zr,Sn,Ti）O₃（PLZST）AFEs were chosen as the research object.Firstly,on the basis of the research on the energy storage properties of（Pb,Ba,La）（Zr,Sn,Ti）O₃（PBLZST）tetragonal phase and（Pb,La）（Zr,Sn,Ti）O₃（PLZST）orthorhombic phase AFE ceramics,the energy storage density and temperature stability of PLZST AFE ceramics were improved by designing the composite ceramics via traditional solid sintering method.Secondly,in view of the high energy storage efficiency of linear Ca（Zr,Ti）O₃（CZT）,the energy storage density and energy storage efficiency of PLZST-based AFE ceramic were improved by designing the PBLZST-CZT composite ceramics.Finally,the traditional solid sintering method and the spark plasma sintering（SPS）method were used to prepare the PLZST/PBLZST/CZT ternary composite ceramics,and the energy storage density,energy storage efficiency and temperature stability were improved simultaneously.The research content is as follows:Research on tetragonal PBLZST:The effect of Ba²⁺substitution on the energy storage density and temperature stability was studied.The substitution of Ba²⁺ions at A-site can weaken the antiferroelectric property of PLZST,and the FE phase was more easily induced,which is conducive to the acquisition of high polarization and energy storage density.However,the introduction of Ba²⁺will lead to the decrease of Curie temperature,which will not be conducive to the temperature stability of energy storage density.Therefore,the energy storage density and temperature stability of tetragonal PBLZST AFE ceramics could be controlled by introducing appropriate Ba²⁺content.When the Ba²⁺content was x=0.03-0.06,the ceramics had higher energy storage density and temperature stability in the temperature range of 20℃to 120℃.For example,when x=0.06,the recoverable energy storage density changed from 2.4 J/cm³ to 2.2 J/cm³,the variation is less than 10%.Research on orthorhombic PLZST:The energy storage properties,especially the temperature stability,of PLZST orthorhombic ceramics were well studied via fine-tuning the ratio of Zr/Sn/Ti.The phase transitions was in the sequence of AFE orthorhombic phase to AFE tetragonal phase to PE cubic phase during the heating.The Curie temperature of orthorhombic is usually higher than that of the tetragonal phase.However,because of the high transition field,the energy storage density at room temperature was low.Therefore,the orthorhombic phase ceramics had good energy density（2.0-3.4 J/cm³）and high efficiency of 71-79%at high temperature（100-175°C）rather than room temperature.In addition,through the analysis of temperature-dependent dielectric properties,XRD patterns,Raman spectra and P-E loops,and electric field-dependent P-E loop,this paper attempted to establish the temperature-electric field phase diagram of the orthorhombic phase PLZST and analyze the energy storage characteristics.Research on improving the temperature stability:According to the previous research,the tetragonal phase has good energy storage characteristics in the low temperature region（25-120℃）,and the energy storage density has a negative temperature coefficient.While,the orthorhombic phase has excellent energy storage characteristics in the high temperature region（100-175℃）,and the energy storage density has a positive temperature coefficient.Therefore,the composite ceamics can be used to combine the advantages of the tetragonal phase and the orthorhombic phase,so as to improve the energy storage density and temperature stability,and expand the temperature range.The preparation process of composite ceramics was studied firstly,and it was found that preprocessing the tetragonal at a higher temperature benefited the energy storage density and temperature stability.Then,the energy storage density and temperature stability of the composite ceramics were remarkably improved by adjusting the content of the orthorhombic phase.High energy storage density of 3.20 J/cm³ at 20 ^oC with a variation of-13.44%（less than 15%）over a temperature range from 20 ^oC to 150 ^oC were found in the composite ceramics with the PLZST content of 55 wt%.Compared with the reported literatures,these composite ceramics broadened the temperature range of PLZST-based AFE energy storage ceramics,and improved the temperature stability of energy storage density.Research on improving the energy storage efficiency:CZT is a kind of linear dielectrics with low dielectric loss,high dielectric breakdown strength（BDS）and small dielectric constant.Although its energy storage density is difficult to be compared with PLZST-based anti-ferroelectric,the energy storage efficiency up to 90%is difficult to achieve in PLZST anti-ferroelectric materials.Besides,the phase diffusion is inevitable at high temperature.From the perspective of tolerance factor,the ionic radius of Ca²⁺is smaller than that of Pb²⁺,La²⁺and Ba²⁺,and the introduction of Ca²⁺can help to stabilize the AFE phase,thus contributing to the improvement of energy storage properties.In addition,the electronegativity of Pb²⁺is greater than that of Ca²⁺,so the difference of electronegativity of Ca-O is greater than that of Pb-O.The introduction of Ca²⁺is conducive to the stability of the structure.At the same time,high BDS of CZT is helpful to enhance the BDS of the composite ceramics and further enhance the energy storage properties.In this paper,the tetragonal PBLZST AFE and CZT linear dielectric were composited to achieve high energy storage density and energy storage efficiency simultaneously.The recoverable energy storage density W_rec increased from 2.69 J/cm³ in PBLZST ceramics to 4.14 J/cm³ in PBLZST-1wt%CZT ceramics,while the efficiency increased from 77%in PBLZST ceramics to 94%in PBLZST-3wt%CZT ceramics.Research on improving the energy storage properties of PLZST-based AFE ceramics by ternary composite ceramics strategy:The energy storage density,energy storage efficiency and temperature stability of PLZST-based AFE ceramics were effectively improved by the design of PLZST/PBLZST/CZT ternary composite ceramics.The storage density of PBLZST-PLZST-0.5 wt%CZT ceramics at 150℃is 4.42 J/cm³,energy storage efficiency is87%,with a variation of-10.53%.Research on improving the energy storage properties of ternary composite ceramics by SPS:In this paper,the energy storage density,energy storage efficiency and temperature stability of samples prepared by SPS with different contents CZT were studied.Due to the rapid heating rate,low sintering temperature,and short sintering time,the diffusion of PLZST,PBLZST and CZT were effectively suppressed by SPS technology,and the comprehensive energy storage performance of the composite ceramics were improved.The energy storage density W_rec increased from 6.47 J/cm³ in PLZST-PBLZST ceramics to 7.07 J/cm³ in PLZST-PBLZST-2 wt%CZT ceramics.The corresponding energy storage efficiency increased from67%to 84%,with an increase of 17%.At 150℃,the energy storage density changed less than 15%,sharing a change of-10.16%.