Study On The Energy Storage Characteristics Of Ba-,Mn-Doped NBT-ST Based Lead-Free Ceramics

Recently,(Na_1/2Bi_1/2)TiO₃?NBT?ceramics was increasingly studied in energy storage applications.Pure NBT ceramics showed high Curie temperature?320??,high coercive field and high remnant polarization,leading to obtained low energy storage density.The goal to reaching higher efficiency for energy storage an application in NBT ceramics was to decrease the remnant polarization while maintaining the saturated polarization,i.e.,make the P-E loops slim by modifying.SrTiO₃?ST?ceramics was paraelectric phase at room temperature,which possess relatively high dielectric constant??_r³00?and high breakdown strength?E_b¹0 kV/mm?suitable for energy storage applications.In this work,ST was selected to modify the ferroelectric properties of NBT ceramics,in order to obtain NBT-ST ceramics with an optimized high energy storage density.Firstly,(Na_1/2Bi_1/2)_1-xSr_xTiO₃?NBT-xST,0.2?x?0.3?lead-free ceramics was selected to investigate the influence of x value on the phase structure,microstructure,dielectric properties and energy storage characteristics of the ceramics.The results showed that the NBT-xST ceramics was pure perovskite structure at room temperature,and an MPB with coexistence of rhombohedral-tetragonal phases was existed when x?0.22.The ceramic grains were packed closely with high density.The dielectric properties of NBT-xST ceramics have strong frequency dependence.With the increasing of x content,the Curie temperature of NBT-xST ceramics was gradually moved to lower temperature.The coercive electric field and remnant polarization of NBT-xST ceramics decreased with the increase of x value.0.74NBT-0.26ST ceramics has good dielectric properties and optimal energy storage properties at room temperature,showing high dielectric constant??_r=2331?,low dielectric loss(tan?=7.6×10^-4,and energy storage density of 0.3 J/cm³ suitable for dielectric energy storage applications.Secondly,the optimized composition of 0.74(Bi_1/2Na_1/2)TiO₃-0.26SrTiO₃ ceramics was selected as base material,while the Ba²⁺ion was introduced to A-site of the crystal lattice of the ceramics.The?0.74-x?(Na_1/2Bi_1/2)TiO₃-0.26SrTiO₃-xBaTiO₃ ceramics was prepared to study the influence of Ba²⁺ions x value on the phase structure,microstructure,dielectric properties and energy storage characteristics of the ceramics.The results showed that the phase changed from quasi cubic to tetragonal with the increase of Ba²⁺ions x content,and two phases co-existing zone happens at 0.04?x?0.06.The grain size was refined and the density improved with x value.With the increasing of Ba²⁺ions x content,the dielectric peak temperature T_m was gradually moved to lower temperature,from 153?of x=0 to 98?of x=0.1,while dielectric constant peak was significantly increased from 7831 to 9481.The ferroelectricity was weakened with the reduction of coercive electric field and remnant polarization by introduction of Ba²⁺ions.When x=0.04,the ceramics presented a weak double P-E loop with energy storage density of0.47J/cm³,showing 1.55 times that of pure 0.74NBT-0.26ST ceramics.In addition to relatively high energy efficiency of 48.67%,the doping of BT effectively expanded the energy storage application of NBT-ST ceramics.Finally,0.7NBT-0.26ST-0.04BT ceramics was selected as base material,and the Mn was introduced?x,x=0,0.1%,0.3%,0.5%,0.7%?,the influence of Mn doping on the phase structure,microstructure,dielectric properties and energy storage characteristics of the ceramics was investigated.The results showed the Mn was presented as Mn²⁺and Mn³⁺ions in the solid solution of Mn doped 0.7NBT-0.26ST-0.04BT ceramics.The lattice expands after Mn doping,while the excess Mn mainly distributed to the grain boundary or grain growth triangle grain boundary to restrict the grain growth and improve the density.Mn doping can effectively improve the breakdown strength of the ceramic and significantly reduce the dielectric loss at higher temperature.With the increasing of Mn content,the dielectric peak temperature T_m was gradually moved to higher temperature,from 130?of x=0 to 187?of x=0.7%.The dielectric constant peak was significantly depressed and widened at the Mn content x=0.5%.When x=0.5%,there was an antiferroelectric-ferroelectric phase transition,and the energy storage density was 0.63J/cm³,showing 1.34 times that of pure 0.7NBT-0.26ST-0.04BT ceramics.Together with higher energy efficiency was 65%,this ceramics should be promising for high energy storage ceramic capacitors.