KNN对BNBST陶瓷储能特性的影响

Effect of KNN on Energy Storage Performance of BNBST Ceramics

具有优异储能特能及温度稳定性的电介质电容器是电子工业的理想选择。可用于脉冲功率系统的无铅弛豫铁电陶瓷电容器在低电场条件下表现出较低的有效储能密度(W_(rec))。为了解决这一问题,采用传统固相法设计并制备了Ba_(0.105)Na_(0.325)Bi_(0.325)Sr_(0.245)TiO_(3+x)%K_(0.5)Na_(0.5)NbO_(3)(BNBST-x%KNN,摩尔分数,x=0、2、4、6、8、10、12)陶瓷,研究了不同KNN掺杂量对BNBST陶瓷的相结构、微观形貌、介电性能、储能特性和充放电特性的影响规律。结果表明:当x=6时,在较低电场(@140 kV/cm)下即可获得较大的有效储能密度(W_(rec)=1.8 J/cm^(3))和较高的储能效率(η=86%)。同时,BNBST-6%KNN陶瓷在–8~215℃的宽温度范围内获得了3128±15%(@1 kHz)的高介电常数,并在80 kV/cm,20~180℃,10000次电循环等条件下,其电储能均保持良好的温度、频率稳定性与抗疲劳特性。此外,BNBST-6%KNN陶瓷的功率密度P_(D)、放电密度W_(d)在20~140℃温度区间内均能维持良好的温度稳定性,说明其可作为低电场驱动高储能密度脉冲功率电容器制作的候选材料。

Introduction Dielectric materials have critical applications in many fields.Compared with electrochemical energy storage batteries,ceramic capacitors show outstanding competitive power performance in actual energy storage applications,such as diesel engine starters,camera flashlights,spacecraft,pulsed power weapons,and medical devices due to their ultra-fast charge/discharge capability and high-power density.However,with the development of electronic device integration and miniaturization,capacitors are required to have a high effective energy storage density(W_(rec))under low electric field.The existing dielectric ceramic capacitors are difficult to meet the corresponding requirements,so it is urgent and significant to develop dielectric ceramic capacitors that can obtain high energy storage density under low voltage.In recent years,the co-design strategy has been used as a typical and effective method to enhance the energy storage performance of BNT,which is achieved by adding different kinds of ABO3 perovskites and various doping ions.Co-design strategy improves energy storage properties by compositional design to induce the formation of polar nanoregions(PNRs)as a result of A/B site ion disordering or structural phase transitions.In this paper,KNN was added to BNBST ceramics to modify the internal crystal structure,and the effect of KNN on the phase structure,microstructure,dielectric properties,energy storage properties,ferroelectric stability and fast charge-discharge characteristics of BNBST ceramics were investigated.Methods As we know,high Pmax,low Pr and high breakdown strengthen Eb are required for dielectric ceramics to achieve high W_(rec).To obtain high energy storage density under a low electric field,we chose Ba_(0.105)Na_(0.325)Bi_(0.325)Sr_(0.245)TiO_(3)(BNBST)with large Pmax and high Curie temperature as the research object,the co-design strategy with the introduction of K_(0.5)Na_(0.5)NbO_(3) was adopted to further destroy the ordered arrangement of A/B position ions,reduce their residual polarization intensity Pr,and optimize their electric polarization behavior.Using solid-state method prepared Ba_((0.105)Na_(0.325)Bi_(0.325)Sr_(0.245)TiO_(3+x)%K_(0.5)Na_(0.5)NbO_(3)(BNBST-x%KNN,mole fraction,x=0,2,4,6,8,10,12)ceramic samples.Bi_(2)O_(3)(99.999%),K_(2)CO_(3)(99%),BaCO_(3)(99%),SrCO_(3)(99%),Na_(2)CO_(3)(99.8%),TiO_(2)(99%),Nb_(2)O_(5)(99.95%)were used as synthetic raw materials to prepare samples according to the following process:1)Accurately weigh the ingredients according to the corresponding stoichiometric ratio,put them in the nylon ball mill tank for 24 h,dry,grind,and pass 80 mesh sieve;2)Pre-burning after pressing into large sections,heating up to 850℃with a heating rate of 5℃/min and holding for 3 h to exclude CO_(2) and pre-synthesize the powder;3)The large pieces are ground into powder,passed through an 80-mesh sieve,ball milling again for 24 h,drying,adding 5%concentration of PVA adhesive for granulation,pressing into a small disc with thickness of about 1 mm,diameter of about 13 mm(pressure(120±10)MPa);4)The small disc was heated to 650℃for 3 h to remove organic matter,and then heated to 1240℃for 2 h to sintering;5)After polished and silvered,heating up 30 min at 650℃,and then various electrical properties are tested.Results and discussion All BNBST-x%KNN ceramics have a single perovskite pseudo-cubic phase structure,and no second phase is generated.The grain distribution of all ceramics is uniform and the density is good.When x=6,the optimized energy storage characteristics are obtained only at the low electric field of 140 kV/cm with W_(rec)=1.8 J/cm^(3) andη=86%.Whatmore,BNBST-6%KNN ceramics have TCC=±15%high dielectric constant(εr=3128@125℃)and excellent temperature,frequency,cycle stability and fast charge–discharge characteristics in the temperature range of–8–215℃.The results show that BNBST-6%KNN ceramics can be used as a candidate material for pulsed power capacitors,and has obvious advantages in low electric field application.Conclusions The main innovation points of this paper are summarized as following.A collaborative design strategy with the introduction of K_(0.5)Na_(0.5)NbO_(3) was used to further destroy the ordered arrangement of A/B ions and promote the formation of polar nanodomains(PNRs),under a certain electric field,PNRs can be transformed into long-range ordered ferroelectric domains,resulting in larger P_(max).When the electric field is removed,the ferroelectric domains formed by PNRs will quickly break back to the initial state,resulting in smaller Pr.More importantly,“premature saturation”is delayed due to the appearance of PNRs,which can obtain hight larger P_(max) at low electric field,resulting in a high W_(rec)=1.8 J/cm^(3) at the low electric field of 140 kV/cm.