| Dielectric materials for energy storage application have the advantages of high power density,fast charge and discharge rates,good thermal stability,and strong aging resistance,which makes dielectric materials widely used in power electronic systems,especially in the field of high-energy pulsed power technology.However,the energy storage density of dielectric energy storage materials are relatively low,which is the critical point in developing of dielectric energy storage materials.Relaxor ferroelectric materials is a typical dielectric energy storage materials,which has the potential to achieve both high energy storage density and high energy storage efficiency due to their high dielectric constant,low remnant polarization,and "linear"hysteresis loop.BaTiO3,known as "the backbone of the electronic ceramic industry",is one of the most widely used ferroelectric materials.It exhibits many distinctive and useful properties,such as large dielectric constant,small dielectric loss,strong electric field resistance,and good insulation,thus,BaTiO3 received extensive attention and research in the fields of dielectric,ferroelectric,piezoelectric,etc.However,the relatively high remnant polarization and the weak thermal stability of dielectric properties impede its application in dielectric energy storage devices.In this work,we prepared BaTiO3-Bi(B'B")O3 solid solution by doping Bi-based perovskite structure into BaTiO3 to improve the dielectric energy storage properties.In BaTiO3-Bi(B'B")O3(where B'B" is a trivalent ion or the combination of a monovalent,divalent ion and a tetravalent,pentavalent,or hexavalent ion),Bi3+and(B'B")3+replaced Ba2+and Ti4+in A site and B site of BaTiO3,respectively.According to the law of crystal chemistry,the doping of Bi(B'B")O3 decreases the tolerance of perovskite structure in BaTiO3,which plays an important role on the dielectric properties,inducing the dielectric relaxor behavior.The doping of Bi(B'B")O3 destroyed the long-range ordered ferroelectric tetragonal structure of BaTiO3,while there are polar clusters on the nanoscale,known as polar nanoregions(PNRs).The appearance of PNRs makes the coexist of polar ferroelectric phase and nonpolar paraelectric phase possible in a wide temperature range.Furthermore,compared with normal ferroelectrics,the appearance of PNRs in relaxor ferroelectrics makes the samples are easier to be polarized under electric field.Thus,this work is focused on the structural characteristics,relaxor behavior and energy storage properties of BaTiO3-based relaxor ferroelectrics.In this work,BaTiO3-based solid solution ferroelectric ceramics(1-x)BaiTiO3-xBi(B'B")O3(BT-BiB'B")3 where B'=Mg2+,Zn2+and B"=Sn4+,Zr4+,Nb5+,Ta5+ were prepared by the solid state reaction.The structural characteristics of BT-BiMgSn,BT-BiMgZr,BT-BiZnZr,BT-BiMgNb,BT-BiZnNb,BT-BiMgTa,BT-BiZnTa were analyzed.XRD results show that a phase transition of tetragonal phase to cubic phase occurs at 0.04?x?0.08,meanwhile,the unit cell expands with the affection of the ionic radius.SEM results show that the micro-morphology of the samples are dense with less pores,and smaller grain size were obtained during the sintering process,which helps to increase the breakdown strength.The EDS results show that each element is uniformly distributed at grains and grain boundaries,and the element percentage is basically consistent with the stoichiometric,which confirms the chemical uniformity of the samples.Raman results show that the change of the characteristic peaks is consistent with the change of the phase.At the same time,with the increase content of x,the polar clusters enriched with elements on the nanoscale caused the variation of characteristic peaks,confirming the existence of PNRs.The dielectric behavior of BT-BiMgSn,BT-BiMgZr,BT-BiZnZr,BT-BiMgNb,BT-BiZnNb,BT-BiMgTa,BT-BiZnTa were analyzed.The results of the temperature-dependent dielectric properties exhibit that with x ?0.04,the results indicate the typical characteristics of normal ferroelectrics.With x>0.08,there appears dispersive phase transition and frequency dispersion.In order to further study the mechanism of the temperature-dependent relaxor behavior,the relaxor degree was obtained by fitting the modified Curie-Weiss law,and the high value of y confirms the high relaxor degree with x>0.08.Furthermore,the Vogel-Fulcher relationship and the temperature-dependent 1/? were analyzed.The value of relaxor parameters TB,Tf,Ea also confirms that the samples exhibits excellent relaxor behavior with x>0.08.The ferroelectric performance and the energy storage properties of BT-BiMgSn,BT-BiMgZr,BT-BiZnZr,BT-BiMgNb,BT-BiZnNb,BT-BiMgTa,BT-BiZnTa were analyzed.The hysteresis loops show that with the increase content of x,the maximum polarization and remnant polarization decreases,the coercive field decreases,and the hysteresis loops become more "slim" and "linear".With x>0.08,the remnant polarization and coercive field are almost negligible.The hysteresis loops under different electric fields exhibit that at lower electric fields,with the increase content of x,the energy storage density Wrec increases initially and then decreases,and the energy storage efficiency ?exhibits a rising trend.At higher electric fields,as the electric field increases,the energy storage density Wrec increases gradually,while the energy storage efficiency ? decreases.With the increase content of x,the optimal energy storage properties achieve at 0.09 ?x?0.16.The optimal results of energy storage properties for the six series are:(1)For BT-BiMgSn,the energy storage density is 3.61 J/cm3 and the energy storage efficiency is 92.8%with x=0.14 at the breakdown strength 370 kV/cm.(2)For BT-BiMgZr,the energy storage density is 2.05 J/cm3 and the energy storage efficiency is 92.0%with x=0.15 at the breakdown strength 240 kV/cm.(3)For BT-BiZnZr,the energy storage density is 2.47 J/cm3 and the energy storage efficiency is 94.4%with x=0.12 at the breakdown strength 250 kV/cm.(4)For BT-BiMgNb,the energy storage density is 6.40 J/cm3 and the energy storage efficiency is 95.6%with x=0.16 at the breakdown strength 590 kV/cm.(5)For BT-BiZnNb,the energy storage density is 3.04 J/cm3 and the energy storage efficiency is 98.8%with x=0.12 at the breakdown strength 300 kV/cm.(6)For BT-BiMgTa,the energy storage density is 3.37 J/cm3 and the energy storage efficiency is 88.1%with x=0.12 at the breakdown strength 310 kV/cm.(7)For BT-BiZnTa,the energy storage density is 3.96 J/cm3 and the energy storage efficiency is 89.6%with x=0.09 at the breakdown strength 450 kV/cm.Furthermore,the thermal stability of energy storage properties for BT-BiMgSn,BT-BiZnNb,and BT-BiZnTa were measured.(1)The variation of energy storage density for 0.86BT-0.14BiMgSn relaxor ferroelectric ceramics is less than 8.0%with the energy efficiency over 90%under 200 kV/cm in the temperature range of 20-120?.The variation of energy storage density is less than 8.5%with the energy efficiency over 80%under 200 kV/cm in the frequency range of 0.1-10 Hz.(2)The variation of energy storage density for 0.88BT-0.12BiZnNb relaxor ferroelectric ceramics is less than 7.7%with the energy efficiency over 88%under 200 kV/cm in the temperature range of 20-160?.The variation of energy storage density is less than 12%with the energy efficiency over 80%under 200 kV/cm in the frequency range of 0.1-10 Hz.(3)The variation of energy storage density for 0.91 BT-0.09BiZnTa relaxor ferroelectric ceramics is less than 6.0%with the energy efficiency over 89%under 200 kV/cm in the temperature range of 20-160?In this work,we obtained a high energy storage properties with high energy storage density and high energy storage efficiency by adjusting the composition of the(1-x)BaTiO3-xBi(B'B")O3 system to construct relaxed ferroelectrics.The results have confirmed the excellent potential of BaTiO3-based relaxation ferroelectrics in dielectric energy storage application. |
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