Influence of Composition on Properties of Medium Temperature Sintering (Ba,Sr)TiO_3 Series Capacitor Ceramics

The influence of the composition （Yb2O3, MgO, CeO2, Li2CO3） on the dielectric properties of medium temperature sintering （Ba, Sr）TiO3 （BST） series capacitor ceramics was investigated by means of conventional technology process and orthogonal design experiments. The major secondary influencing factors and the influencing tendency of various factor＇s levels for the dielectric properties of BST ceramics were obtained. The optimum formula for maximum dielectric constant （ε） and for minimum dielectric loss （tanδ） was obtained under the experimental conditions. The BST ceramics with optimum comprehensive properties was obtained by means of orthogonal design experiments, with the sintering temperature at 1200 ℃, the dielectric constant 5239, the dielectric loss 0.0097, withstand electric voltage over 6 MV·m^-1, capacitance temperature changing ence of various components on the providing the basis for preparation rate （△C/C） - 75.67%, and suited for Y5V character. The mechanism of the infludielectric properties of medium temperature sintering BST ceramics was studied, thus of multilayer capacitor ceramics and single-chip capacitor ceramics.

Dopant Behaviours of Sm_2O_3 on Microstructure and Properties of Barium Zirconium Titanate Ceramics

The effect of Sm 2O 3 dopant on the sintering characteristics and dielectric properties of barium zirconium titanate ceramics (BaZr x Ti 1- x O 3) was investigated. It is shown that trace amount of Sm 2O 3 can greatly affect the grain growth and densification of barium zirconium titanate ceramics during sintering. At the same time, the dielectric peak at high temperature shifts to lower temperature and that at low temperature shifts to higher temperature. The two dielectric peaks overlap with each other when the Sm 2O 3 dopant content varies from 0 25% to 1%, and the maximum relative dielectric constant is greatly enhanced. These effects may be attributed to the substitution actions of the rare earth element in perovskite lattice. At the doping content of 0 75%, the dielectric constant maximum of 23570 can be obtained. By adopting some proper additives, an excellent Y5V dielective material is obtained, and the room temperature properties are as follows: relative dielectric constant ε RT ≥23,000, dielectric loss tgδ≤0 0075 and the breakdown strength under alternating field E b≥5 kV·mm -1 .

Effect of SiO_2 addition on the dielectric properties and microstructure of BaTiO_3-based ceramics in reducing sintering

The effect of SiO2 doping on the sintering behavior, microstructure, and dielectric properties of BaTiO3-based ceramics has been investigated. Silica was added to the BaTiO3-based powder prepared by the solid state method with 0.075mol%, 0.15mol%, and 0.3mol%, respectively. The SiO2-doped BaTiO3-based ceramic with high density and uniform grain size were obtained, which were sintered in reducing atmosphere. A scanning electron microscope, X-ray diffraction, and LCR meter were used to determine the microstructure as well as the dielectric properties. SiO2 can form a liquid phase belonging to the ternary system of BaO-TiO2-SiO2, leading to the formation of BaTiO3 ceramics with high density at a lower sintering temperature. The SiO2-doped BaTiO3-based ceramics can be sintered to a theoretical density higher than 95% at 1220℃ with a soaking time of 2 h. The dielectric constants of the sample with 0.15mol% SiO2 addition sintered at 1220℃ is about 9000. Doping with a small amount of silica can improve the sintering and dielectric properties of BaTiO3-based ceramics.

Dielectric Properties and Structure of Yb_2O_3-Doped (Ba,Sr)TiO_3 Ceramics

The effect of Yb2O3 doping amount on the dielectric properties of (Ba, Sr)TiO3 (BST) series capacitor ceramics prepared using solid state reaction method were studied. With the increasing of Yb2O3 doping amount, the dielectric constant(ε) of materials increased, the dielectric loss(tanδ) of materials decreased to minimum when w(Yb2O3) was 0.9%. The BST ceramics with high ε(10000), low tanδ(0.0213) and high DC breakdown voltage(7.2 kV·mm-1) were obtained. The influence of Yb2O3 doping amount on the structure of BST ceramics was studied by means of X-ray diffraction(XRD) and scanning electron microscope. The influencing mechanism of Yb2O3 on the dielectric properties of BST ceramics was studied. The results showed that Yb2O3 doping influenced the properties and structure of BST ceramics by means of forming defect solid solution, but did not influence crystal grain size,the crystal phase was single perovskite structure, did not influence XRD data of BST and did not improve capacitance temperature property greatly, but increase dielectric constant greatly. These results provided the basis for Yb2O3-doped BST series capacitor ceramics.

Excellent energy storage properties in non-stoichiometric Bi_(0.5)Na_(0.5)TiO_(3)-based relaxor ferroelectric ceramics

The rapid development of high-power and pulsed-power techniques inspires extensive investigates on high-performance ceramic-based capacitors.However,the low recoverable energy density(Wrec)hampers their wider applications.Herein,the non-stoichiometric Bi_(0.5)Na_(0.5)TiO_(3)-based ceramics were designed and studied.The proper introduction of oxygen vacancies facilitated activating defect dipole,giving rise to reduced remanent polarization.Consequently,the optimal composition exhibited an exceptional high Wrec of 8.3 J/cm^(3),a high efficiency of 85%,and excellent anti-fatigue and thermal reliability.This work provides an efficient approach to explore ceramic capacitors with high capacitive energy storage performances.

Glass modified barium strontium titanate ceramics for energy storage capacitor at elevated temperatures

A glass with composition of B_(2)O_(3)-Bi_(2)O_(3)-SiO_(2)-CaO-BaO-Al_(2)O_(3)-ZrO_(2)(BBSZ)modified Ba_(x)Sr_(1-x)TiO_(3)(BST,x=0.3 and 0.4)ceramics were prepared by a conventional solid state reaction method abided by a formula of BST+y%BBSZ(y=0,2,4,7,and 10,in mass).The effect of BBSZ glass content on the structure,dielectric properties and energy storage characteristics of the ceramics was investigated.The dielectric constant reduced but the endurable electrical strength enhanced due to the BBSZ glass addition in BST ceramics.In particular,the dielectric loss of the ceramics at elevated temperature(e.g.200℃)can be strongly suppressed from tanδ>20%to tanδ<3% after BBSZ glass modification.For Ba_(0.3)Sr_(0.7)TiO_(3)+2%BBSZ ceramics,an optimized energy storage density(γ=0.63 J/cm^(3))and efficiency(η=91.6%)under an applied electric field of 160 kV/cm was obtained at room temperature.Meanwhile,the temperature dependent polarization-electric field(P-E)hysteresis loops were measured to evaluate the energy storage characteristics of the ceramics potential for high voltage capacitor application at elevated temperatures.

Optimizing the grain size and grain boundary morphology of (K,Na) NbO_(3)-based ceramics: Paving the way for ultrahigh energy storage capacitors

Relaxor dielectric ceramic capacitors are very attractive for high-power energy storage.However,the low breakdown strength severely restricts improvements to the energy storage density and practical application.Here,a strategy of designing small grain sizes and abundant amorphous grain boundaries is proposed to improve the energy storage properties under the guidance of phase field theory.0.925(K_(0.5)Na_(0.5))NbO_(3)-e0.075Bi(Zn_(2/3)(Ta_(0.5)Nb_(0.5))1/3)O_(3)(KNNe-BZTN)relaxor ferroelectric ceramic is taken as an example to verify our strategy.The grain sizes and grain boundaries of the KNNeBZTN ceramics are carefully controlled by the high-energy ball milling method and twoestep sintering strategy.Impedance analysis and diffusion reflectance spectra demonstrate that KNNeBZTN ceramics with a small grain size and abundant amorphous grain boundary exhibit a lower charge carrier concentration and higher band gap.As a consequence,the breakdown electric field of KNNeBZTN ceramics increases from 222 kV/cm to 317 kV/cm when the grain size is decreased from 410 nm to 200 nm,accompanied by a slightly degraded maximum polarization.KNNeBZTN ceramics with an average grain size of~250 nm and abundant amorphous grain boundaries exhibit optimum energy storage properties with a high recoverable energy density of 4.02 J/cm^(3) and a high energy efficiency of 87.4%.This successful local structural design opens up a new paradigm to improve the energy storage performance of other dielectric ceramic capacitors for electrical energy storage.

Preparation of spherical ultrafine copper powder via hydrogen reduction-densification of Mg(OH)_2-coated Cu_2O powder

A novel process was developed to produce spherical copper powder for multilayer ceramic capacitors （MLCC）. Spherical ultrafine cuprous oxide （Cu20） powder was prepared by glucose reduction of Cu（OH）2. The Cu20 particles were coated by Mg（OH）2 and reduced to metallic copper particles. At last, the copper particles were densified by high-temperature heat treatment. The products were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, tap density, and thermogravimetry （TG）. It is found that the shape and size distribution of the copper powder are determined by the Cu20 powder and the copper particles do not agglomerate during high-temperature heat treatment because of the existence of Mg（OH）2 coating. After densification at high temperature, the particle tap density increases from 3.30 to 4.18 g/cm3 and the initial oxidation temperature rises from 125 to 150~C.

A Technology for Recovering Silver and Palladium from MLCC Scraps

technology for recovering silver and palladium from multilayer ceramic capacitors (MLCC) scraps was studied. 91% silver and 98% palladium are respectively leached from scraps (200 mesh) under the conditions of 4 mol/L HNO_3, 80℃, 2 h (s/l=1∶3). Silver can be precipitated with hydrochloric acid from leaching solutions. Purity of coarse silver bullion obtained from melting silver chloride is 98%. Silver recovery is 88%. Palladium can be reduced and precipitated respectively from silver raffinate and leaching residue scrub solutions by iron powders and butyl xanthate. Purity of palladium is 99.95% by traditional refining method. Palladium recovery is 95%.

Superior energy storage efficiency through tailoring relaxor behavior and band energy gap in KNN-based ferroelectric ceramic capacitors

With the increasing demand of high-power and pulsed power electronic devices,environmental-friendly potassium sodium niobate((Na_(0.5)K_(0.5))NbO_(3),KNN)ceramic-based capacitors have attracted much attention in recent years owning to the boosted energy storage density(W_(rec)).Nevertheless,the dielectric loss also increases as the external electric field increases,which will generate much dissipated energy and raise the temperature of ceramic capacitors.Thus,an effective strategy is proposed to enhance the energy storage efficiency(η)via tailoring relaxor behavior and bad gap energy in the ferroelectric 0.9(Na_(0.5)K_(0.5))-NbO_(3)-0.1Bi(Zn_(2/3)(Nb_(x)Ta_(1−x))1/3)O_(3) ceramics.On the one hand,the more diverse ions in the B-sites owing to introducing the Ta could further disturb the long-range ferroelectric polar order to form the short−range polar nanoregions(PNRs),resulting in the highη.On the other hand,the introduction of Ta ions could boost the intrinsic band energy gap and thus improve the Eb.As a result,high Wrec of 3.29 J/cm^(3) and ultrahighηof 90.1%at the high external electric field of 310 kV/cm are achieved in x=0.5 sample.These results reveal that the KNN-based ceramics are promising lead-free candidate for high-power electronic devices.

Enhanced breakdown strength of BaTiO_(3)-based multilayer ceramic capacitor by structural optimization

0.5 wt%Nb_(2)O_(5)doped 0.12BiAlO_(3)-0.88BaTiO_(3)(12BA5N)multilayer ceramic capacitor(MLCC-1)was prepared,which satisfied EIA X7R specification(where X is the minimum temperature,R is the percentage of capacitance variation limit)at 1 kHZ.The distribution of internal electric field under breakdown voltage was simulated by finite element method(FEM),indicating that the electric field strength increased significantly at the terminal of internal electrode.These areas may become the headstream of breakdown for MLCC-1 due to the shape mutation.In order to improve the breakdown performance of MLCC-1,it was optimized by 12BA5N+2G green sheets(prepared by 12BA5N ceramic powder with 2 wt%B-Al-Si glass additive),then MLCC-2 was obtained which satisfied EIA X8R specification.Its BDS rose from 20 to29.4 kV·mm^(-1),and the electric field distribution of dielectric layer was also analyzed by FEM.Besides,it was also found that the grain size and the dielectric constants of"core"and"shell"parts for the 12BA5N+2G dielectric layer both contributed to the enhanced BDS of MLCC-2according to the simulation results from FEM.

Unusual local electric field concentration in multilayer ceramic capacitors

Local electric-field around multitype pores(dielectric pore,interface pore,electrode pore)in multilayer ceramic capacitors(MLCCs)was investigated using Kelvin probe force microscopy combined with the finite element simulation to understand the effect of pores on the electric reliability of MLCCs.Electricfield is found to be concentrated significantly in the vicinity of these pores and the strength of the local electric-field is 1.5e5.0 times of the nominal strength.Unexpectedly,the concentration degree of the pores in the inner electrode is much higher than that in the dielectrics and dielectric-electrode interfaces.Meanwhile,geometry orientations are found to have a remarkable influence on the local electric field strength.The pores act as an insulation degradation precursor via local electric,thermal center,and oxygen vacancies accumulation center.Such unusual local electric field concentration of multitype pores can provide new insights into the understanding of insulation degradation evolution,processing tailoring and design optimization for MLCCs.

Perspectives and challenges for lead-free energy-storage multilayer ceramic capacitors

The growing demand for high-power-density electric and electronic systems has encouraged the development of energy-storage capacitors with attributes such as high energy density,high capacitance density,high voltage and frequency,low weight,high-temperature operability,and environmental friendliness.Compared with their electrolytic and film counterparts,energy-storage multilayer ceramic capacitors(MLCCs)stand out for their extremely low equivalent series resistance and equivalent series inductance,high current handling capability,and high-temperature stability.These characteristics are important for applications including fast-switching third-generation wide-bandgap semiconductors in electric vehicles,5G base stations,clean energy generation,and smart grids.There have been numerous reports on state-of-the-art MLCC energy-storage solutions.However,lead-free capacitors generally have a low-energy density,and high-energy density capacitors frequently contain lead,which is a key issue that hinders their broad application.In this review,we present perspectives and challenges for lead-free energy-storage MLCCs.Initially,the energy-storage mechanism and device characterization are introduced;then,dielectric ceramics for energy-storage applications with aspects of composition and structural optimization are summarized.Progress on state-of-the-art energy-storage MLCCs is discussed after elaboration of the fabrication process and structural design of the electrode.Emerging applications of energy-storage MLCCs are then discussed in terms of advanced pulsed power sources and high-density power converters from a theoretical and technological point of view.Finally,the challenges and future prospects for industrialization of lab-scale lead-free energy-storage MLCCs are discussed.

Energy storage properties of 0.87BaTiO3-0.i3Bi(Zn2/3(Nb0.85Ta0.15)1/3)O3 multilayer ceramic capacitors with thin dielectric layers

Multilayer ceramic capacitors(MLCCs)for energy storage applications require a large discharge energy density and high discharge/charge efficiency under high electric fields.Here,0.87BaTiO3--0.13Bi(Zn23(Nbog8sTao.1s)u3)O3(BTBZNT)MLCCs with double active dielectric layers were fabricated,and the effects of inner electrode and sintering method on the energy storage properties of BTBZNT MLCCs were investigated.By using the pure Pt as inner electrode instead of Ago.6Pdo4 aloys,an alternating current(AC)breakdown strength(BDS)enhancement from 1047 to 1500 kV/cm was achieved.By investigating the leakage current behavior of BTBZNT MLCCs,the Pt inner electrode and two-step sintering method(TSS)were confirmed to enhance the Schottky barrier and minimize the leakage current density.With relatively high permitivity,dielectric sublinearity,and ultra-high BDS,the Pt TSS BTBZNT MLCCs exhibited a surprisingly discharge energy density(Udis)of 14.08 J/cm2.Moreover,under an operating electric field of 400 kV/cm,the MLCCs also exhibited thermal stability with Udis variation<±8%over a wide temperature (t) range from-50 to 175℃ and cycling reliability with Uais reduction<0.3%after 3000 charge-discharge cycles.These remarkable performances make Pt TSS BTBZNT MLCCs promising for energy storage applications.

Remarkably enhanced dielectric stability and energy storage properties in BNT–BST relaxor ceramics by A-site defect engineering for pulsed power applications

Lead-free bulk ceramics for advanced pulsed power capacitors show relatively low recoverable energy storage density(Wrec)especially at low electric field condition.To address this challenge,we propose an A-site defect engineering to optimize the electric polarization behavior by disrupting the orderly arrangement of A-site ions,in which Ba_(0.105)Na_(0.325)Sr_(0.245−1.5x)□_(0.5x)Bi_(0.325)+xTiO_(3)(BNS_(0.245−1.5x)□_(0.5x)B_(0.325+x)T,x=0,0.02,0.04,0.06,and 0.08)lead-free ceramics are selected as the representative.The BNS_(0.245−1.5x)□_(0.5x)B_(0.325+x)T ceramics are prepared by using pressureless solid-state sintering and achieve large W_(rec)(1.8 J/cm^(3))at a low electric field(@110 kV/cm)when x=0.06.The value of 1.8 J/cm3 is super high as compared to all other W_(rec) in lead-free bulk ceramics under a relatively low electric field(<160 kV/cm).Furthermore,a high dielectric constant of 2930 within 15%fluctuation in a wide temperature range of 40–350℃is also obtained in BNS_(0.245−1.5x)□_(0.5x)B_(0.325+x)T(x=0.06)ceramics.The excellent performances can be attributed to the A-site defect engineering,which can reduce remnant polarization(P_(r))and improve the thermal evolution of polar nanoregions(PNRs).This work confirms that the BNS_(0.245−1.5x)□_(0.5x)B_(0.325+x)T(x=0.06)ceramics are desirable for advanced pulsed power capacitors,and will push the development of a series of Bi0.5Na0.5TiO3(BNT)-based ceramics with high W_(rec) and high-temperature stability.

Achieving excellent energy storage reliability and endurance via mechanical performance optimization strategy in engineered ceramics with core-shell grain structure

Although dielectric ceramic capacitors possess attractive properties for high-power energy storage,their pronounced electrostriction effect and high brittleness are conducive to easy initiation and propagation of cracks that significantly deteriorate electrical reliability and lifetime of capacitors in practical applications.Herein,a new strategy for designing relaxor ferroelectric ceramics with K_(0.5)Na_(0.5)NbO_(3)-core/SiO_(2)-shell structured grains was proposed to simultaneously reduce the electric-field-induced strain and enhance the mechanical strength of the ceramics.The simulation and experiment declared that the bending strength and compression strength of the core-shell structured ceramic were shown to increase by more than 50% over those of the uncoated sample.Meanwhile,the electric-field-induced strain was reduced by almost half after adding the SiO_(2) coating.The suppressed electrical deformation and enhanced mechanical strength could alleviate the probability of generation of cracks and prevent their propagation,thus remarkably improving breakdown strength and fatigue endurance of the ceramics.As a result,an ultra-high breakdown strength of 425 kV cm^(-1) and excellent recoverable energy storage density(Wrec~4.64 J cm^(-3))were achieved in the core-shell structured sample.More importantly,the unique structure could enhance the cycling stability of the ceramic(Wrec variation<±2% after 105 cycles).Thus,mechanical performance optimization via grain structure engineering offers a new paradigm for improving electrical breakdown strength and fatigue endurance of dielectric ceramic capacitors.

Energy storage properties of surface-modified BaTiO_(3)ceramic films for multilayer capacitors applications

Surface-modified BaTiO_(3)of 230 nm average grain size were synthesized by coating BaTiO_(3)particles with 3 wt.%Al2O_(3)and 1 wt.%SiO2.Ceramic films of different thicknesses were prepared via tape casting and laminating processes followed by two-steps sintering method.After sintering,the average grain size of Surface-modified BaTiO_(3)ceramic slightly increased to 275 nm,and great enhancement of AC breakdown strength(BDS)from 184 kV/cm to 665 kV/cm was obtained as the thickness of ceramic films decreased from 63μm to 12μm,resulting in improvement of discharge energy density from 1.14 J/cm3to 4.06 J/cm3.Because of their low-cost,easily fabrication,lead-free,improved AC BDS and discharge energy density,surface-modified BaTiO_(3)ceramic films appeared promising for applications in multilayer energy storage capacitors.

Photonic bands,gap maps,and intrinsic losses in three-component 2D photonic crystal slabs

We obtain the photonic bands and intrinsic losses for the triangular lattice three-component two- dimensional （2D） photonic crystal （PhC） slabs by expanding the electromagnetic field on the basis of waveguide modes of an effective homogeneous waveguide. The introduction of the third component into the 2D PhC slabs influences the photonic band structure and the intrinsic losses of the system. We examine the dependences of the band gap width and gap edge position on the interlayer dielectric constant and interlayer thickness. It is found that the gap edges shift to lower frequencies and the intrinsic losses of each band decrease with the increasing interlayer thickness or dielectric constant. During the design of the real PhC system, the effect of unintentional native oxide surface layer on the optical properties of 2D PhC slabs has to be taken into consideration. At the same time, intentional oxidization of macroporous PhC structure can be utilized to optimize the design.