| Dielectric materials for energy storage have high release power density,fast charge-discharge rate and long cycle life,which are important new power energy storage materials.However,the energy storage density of lead-free dielectric materials is still low due to the restriction of breakdown strength and polarization strength.Therefore,improving the energy storage density of lead-free materials is the focus of research in this field.Among them,relaxor ferroelectrics have the potential to achieve both high energy storage density and high energy storage efficiency due to their high dielectric constant,low remnant polarization and slender hysteresis loops.Bi0.5Na0.5TiO3(BNT)has attracted wide attention due to its similar structure to PbZrO3.In this paper,Bi0.5Na0.5TiO3-BaTiO3 ceramics with energy storage potential were selected as the research object,and a sintering process of"bare sintering+double crucible+slight excess proportion of volatile elements"was designed,and the(Bi0.5Na0.5)0.93Ba0.07(A)Ti(B)O3(where A=La3+,Pr3+ and Sr2+;B=Sn4+,Mn4+,Zr4+ and Nb5+)system of eight ceramic materials.The effects of phase structure,breakdown field strength(Eb),tolerance factor(t),ionic radius,ion valence and other factors on the energy storage performance of ceramics are studied in detail,and the physical mechanism of ceramic materials to obtain higher energy storage density is deeply analyzed.The preparation of lead-free energy storage ceramic materials with high energy storage properties provides a new idea.1.(Bi0.5Na0.5)0.93Ba0.07(A)TiO3(A=La3+,Pr3+ and Sr2+)ceramics formed a single perovskite structure,in which La3+-doped ceramics formed a pseudocubic phase,the doped Pr3+ ceramics form a morphotropic phase boundary(MPB)of tripartite and tetragonal coexistence,and the doped Sr2+ceramics,with the increase of doping amount,the crystal structure of ceramics gradually changes from the MPB to tetragonal and pseudocubic phase;The A-site doping that inhibits the growth of ceramic grains increases the breakdown field strength;The best energy storage performance of ceramics are:Under the electric field of 95 kV/cm,the releasable energy storage density(Wrec)of BNT7BTLa0.o3 ceramic is 0.65 J/cm3,and the energy storage efficiency(η)is 39.50%;under the electric field of 90 kV/cm,the Wrec of BNT7BTPr0.02 ceramic is 1.49 J/cm3,and the η is 63.19%.Under the electric field of 90 kV/cm,the Wrec of BNTBSr0.3 ceramic is 0.86 J/cm3,and the η is 71.83%,and all three show good temperature stability.The three component ceramics with the best energy storage properties have large dielectric constants in a wide frequency range,which are 1100,2250 and 7800,respectively.Their low dielectric losses are 0.12,0.10 and 0.20,respectively.2.The results of(Bi0.5Na0.5)0.93Ba0.07Ti(B)O3(B=Sn4+ and Mn4+)ceramic materials show that(Bi0.5Na0.5)0.93Ba0.07Ti1-xSnxO3 relaxor ferroelectric ceramics show a single perovskite structure,and the ceramics are in tetragonal phase.Sn4+ is uniformly distributed in the matrix ceramics.(Bi0.5Na0.5)0.93Ba0.07Sn0.2Ti0.8-yMnyO3 relaxor ferroelectric ceramics have a small amount of Pyrochlore phase besides perovskite structure.B-site doping promotes the growth of ceramic grains,increases the density,and enhances the breakdown field strength.When x is 0.2,BNT7BTSnx ceramics exhibit double hysteresis loops of antiferroelectric,and antiferroelectric increases with the increase of Sn content.The optimal energy storage properties are as follows:the Wrec of BNT7BTSn0.2 ceramic is 1.27 J/cm3 and the η is 79.15%under the electric field of 150 kV/cm;the Wrec of BNT7BTSMn0.003 ceramic is 1.32 J/cm3 and η is 70.04%under the electric field of 165 kV/cm,and both show good temperature stability.The two component ceramics with the best energy storage properties have large dielectric constants in a wide frequency range of 1950 and 1650,respectively.Their low dielectric losses are 0.08 and 0.12,respectively.3.(1-x)BNT7BTPr0.02-xBNTBSr0.3 relaxor ferroelectric composite ceramics show a single perovskite structure.The crystal structure of the ceramics gradually changes from the MPB to tetragonal and pseudocubic coexistence.With the increase of BNTBSr0.3 content,the growth of ceramic grains is inhibited and the breakdown field strength is improved.When x=0.8,the composite ceramics obtained the best energy storage performance.Under the electric field of 125 kV/cm,the 20BNT7BTPr0.02-80BNTBSr0.3 composite ceramics could release the Wrec of 0.96 J/cm3,and the η was 56.54%,showing excellent temperature stability.The 20BNT7BTPr0.02-80BNTBSr0.3 composite ceramics have large dielectric constant(7800)and low dielectric loss(0.2)in a wide frequency range.The composite ceramics with this ratio broaden the relaxation dielectric temperature range.4.(Bi0.5Na0.5)0.93Ba0.07(A)Ti(B)O3(where A=Pr3+;B=Zr4+and Nb5+)co-doped relaxor ferroelectric ceramics show that the ceramics show a single perovskite structure,and the crystal structure of the ceramics is tetragonal phase and pseudocubic phase.The co-doping of Pr3+and Zr4+ promotes the growth of ceramic grains,while the co-doping of Pr3+and Nb5+ inhibits the growth of ceramic grains.The co-doping of A-B sites increases the polarization difference of the ceramics,which improves the releasable energy storage density and energy efficiency.The optimal energy storage properties are as follows:the Wrec of BNT2Pr7BTZr0.03 ceramic is 1.38 J/cm3 and η is 52.44%under the electric field of 138 kV/cm;the Wrec of BNT2Pr7BTNb0.05 ceramic is 1.85 J/cm3 and the η is 65.75%under the electric field of 140 kV/cm,and both show good temperature stability.The two component ceramics with the best energy storage properties have large dielectric constants in a wide frequency range,which are 1150 and 1250,respectively.Their low dielectric losses are 0.10 and 0.05,respectively.Therefore,in this paper,relaxor ferroelectrics were constructed by adjusting the composition of A and B sites of BNT7BT ceramics,and ceramic materials with high energy storage density and high energy storage efficiency were obtained,which confirmed the great application potential of BNT7BT-based relaxor ferroelectrics in dielectric energy storage. |
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