Synergistically Toughening Effect of SiC Whiskers and Nanoparticles in Al_2O_3-based Composite Ceramic Cutting Tool Material

In recent decades, many additives with different characteristics have been applied to strengthen and toughen Al2O3-based ceramic cutting tool materials. Among them, SiC whiskers and SiC nanoparticles showed excellent performance in improving the material properties. While no attempts have been made to add SiC whiskers and SiC nanoparticles together into the ceramic matrix and the synergistically toughening effects of them have not been studied. An Al2O3-SiCw-SiC np advanced ceramic cutting tool material is fabricated by adding both one-dimensional SiC whiskers and zero-dimensional SiC nanoparticles into the Al2O3 matrix with an effective dispersing and mixing process. The composites with 25 vol% SiC whiskers and 25 vol% SiC nanoparticles alone are also investegated for comparison purposes. Results show that the Al2O3-SiCw-SiCnp composite with both 20 vo1% SiC whiskers and 5 vol% SiC nanoparticles additives have much improved mechanical properties. The flexural strength of Al2O3-SiCw-SiCnp is 730＋ 95 MPa and fracture toughness is 5.6 ± 0.6 MPa.m1/2. The toughening and strengthening mechanisms of SiC whiskers and nanoparticles are studied when they are added either individually or in combination. It is indicated that when SiC whiskers and nanoparticles are added together, the grains are further refined and homogenized, so that the microstructure and fracture mode ratio is modified. The SiC nanoparticles are found helpful to enhance the toughening effects of the SiC whiskers. The proposed research helps to enrich the types of ceramic cutting tool and is benefit to expand the application range of ceramic cutting tool.

Sintering Behavior and Microwave Dielectric Properties of BBSZL Glass-doped ZnTiO_3 Ceramics for LTCC Applications

A novel low temperature co-fired ceramic(LTCC) material was fabricated by zinc titanate(ZnTiO_3) ceramics doped with B_2O_3-BaO-SiO_2-ZnO-Li_2O(BBSZL) glass. The influences of BBSZL glass on wetting behavior, sintering activation energy, phase composition, microstructure and microwave dielectric properties were investigated. The experimental results show that the sintering temperature of ZnTiO3 ceramics can be reduced from 1 100 to 925 ℃, meanwhile the sintering activation energy is decreased from 465.32 to 390.54 kJ·mol^(-1) by BBSZL glass aid, respectively. Moreover, BBSZL glass can inhibit the high Q×f ZnTiO_3 phase decompose into the low Q×f value Zn_2TiO_4 phase, which is propitious to obtain high Q×f value LTCC material. The ZnTiO_3-BBSZL composite sintered at 925℃ displays the excellent microwave dielectric properties with ε_r of 21.8, Q×f value of 42000 GHz, and τ_f of-75 ppm·℃^(-1).

Purification performance on molten steel of novel Al_(2)O_(3)-based ceramic filter prepared from microporous powder and nano-Al_(2)O_(3) powder

Reticulated ceramic foam filters provide an effective way to purify molten steel by removing non-metallic inclusions.We proposed a novel strategy to improve the purification performance of Al_(2)O_(3)-based ceramic filters by using microporous corundum-spinel raw materials to replace dense raw materials.Three kinds of Al_(2)O_(3)-based ceramic filters fabricated from dense α-Al_(2)O_(3) micro-powder or microporous corundum-spinel powder were selected to carry out the immersion tests with molten steel.On the one hand,the higher surface roughness of the filter skeleton prepared from microporous raw materials increased the adsorption capacity of skeleton surface on inclusions in molten steel.On the other hand,the higher apparent porosity and larger pore size of the filter skeleton were more beneficial to the penetration of molten steel in the micropores of skeleton.The reaction process at the solid-liquid interface also improved the wettability of the interface between skeleton and molten steel,resulting in a larger penetration depth and a better adsorption effect on the inclusions.In summary,the novel Al_(2)O_(3)-based ceramic filter prepared with microporous corundum-spinel powder and addition of 5 wt.% nano-Al_(2)O_(3) powder reduced the total oxygen content of the steel from 40.2×10^(-4) to 12.7×10^(-4) wt.% by 68.4% and the Al content from 0.46 to 0.18 wt.% by 60.9% after immersion test,presenting the most excellent purification performance on molten steel.

Ultrahigh electrostrain with excellent fatigue resistance in textured Nb^(5+)-doped(Bi_(0.5)Na_(0.5))TiO3-based piezoceramics

(Bi_(0.5)Na_(0.5))TiO_(3)(BNT)-based lead-free piezoceramics exhibit excellent electric field-induced strain(electrostrain)properties,but often suffer from large hysteresis and poor fatigue resistance,which strongly limit their applications.Here,<00l>textured Nb5+-doped 0.8(Bi_(0.5)Na_(0.5))TiO_(3)–0.2(Bi_(0.5)K_(0.5))TiO_(3)(0.8BNT–0.2BKT)ceramics with a high degree of texturing(~80%)were prepared by the reactive template grain growth(RTGG)method using Bi4Ti3O12 as a template.By the combination of donor doping in the B-site and the RTGG method,the electrostrain performance achieves a significant enhancement.A high electrostrain of 0.65%and a piezoelectric coefficient(*33 d)of 1083 pm/V with reduced hysteresis at an electric field of 6 kV/mm are obtained.No electrostrain performance degradation is observed after unipolar electric field loading of 10^(5)cycles,showing excellent fatigue endurance.These results indicate that the texturing BNT-based lead-free piezoceramics by the RTGG method is a useful approach to developing eco-friendly actuators.

High energy storage properties in Ca_(0.7)La_(0.2)TiO_(3)-modified NaNbO_(3)-based lead-free antiferroelectric ceramics

In this work,(1−x)(0.92NaNbO_(3)-0.08BaTiO_(3))-xCa_(0.7)La_(0.2)TiO_(3)(NNBT-xCLT)ceramics were successfully designed and pre­pared by the solid-state reaction method.Investigations on the structure,dielectric,and energy storage properties were performed.The NNBT-0.25CLT ceramic with orthorhombic phase at room temperature was found to exhibit extremely small grain size and compacted microstructure.A large Wrec of 3.1 J/cm^(3) and a highηof 91.5%under the electric field of 360 kV/cm were achieved simultaneously in the sample.In addition,the energy storage performance of the sample exhibits thermal stability over the tem­perature range of 25-140°C and the frequency range of 5-500 Hz.The charge and discharge tests reveal that the ceramic shows a large current density CD of 965 A/cm2 and power density PD of 154 MW/cm^(3).This work demonstrates that the NNBT-0.25CLT ceramic is a prospective energy storage material for potential application in the field of pulsed power devices.

High energy storage density and power density achieved simultaneously in NaNbO_(3)-based lead-free ceramics via antiferroelectricity enhancement

High-performance lead-free dielectric ceramics with simultaneously high energy storage density and power density are in high demanded for pulse power systems.To realize excellent energy-storage characteristics,a strategy to enhance antiferroelectricity and construct a local random field simultaneously was proposed in this study.Based on the above strategy,a series of(1-x)NaNbO_(3)-xBi(Ni_(1/2)Sn_(1/2))O3[xBNS,x=0.05,0.10,0.15,0.20,and 0.22]solid solutions were designed and fabricated.An ultrahigh energy storage density(Utotal)of 7.35 J/cm^(3),and recoverable energy density(Urec)of 5.00 J/cm^(3) were achieved in the 0.10BNS ceramics.In addition,an adequate stability of energy storage properties at a range of temperatures(20e140℃),frequencies(1e100 Hz),and fatigue test durations(1e1-10^(4) cycles)were realized in 0.10BNS ceramics.0.10BNS ceramics displayed a high current density of 1005 A/cm2,an ultrahigh power density of 100.5 MW/cm^(3,)and an ultrashort discharge time of 46.5 ns?This remarkable performance not only justified our strategy but also confirmed 0.10BNS ceramics as a promising candidate for energy storage.

Effect of Bi_2O_3 Additive on the Microstructure and Dielectric Properties of BaTiO_3-Based Ceramics Sintered at Lower Temperature

High performance X8R dielectric ceramics were prepared by dopingBi2O3 to BaTiO3-based ceramics.The effect of small amounts（≤1.2 mol%） ofBi2O3 additive on the microstructure and dielectric properties of BaTiO3-based ceramics have been investigated.The Bi2O3 ,acting as a sintering additive,can effectively lower the sintering temperature of BaTiO3-based ceramics from 1300 to 1130 °C.The bulk density of BaTiO3-based ceramics increased and reached the maximum value with increasingBi2O3 content.The dielectric constant increased with increasingBi2O3 until it reached the maximum value with 0.8 mol%Bi2O3 additive,and the dielectric loss decreased with increasingBi2O3 content.Optimal dielectric properties of ε=2470,tanδ=0.011 and △ε/ε 25 ≤±9%（-55-150 °C） were obtained for the BaTiO3-based ceramics doped with 0.8 mol%Bi2O3 sintered at 1130 °C for 6 h.

Optimized strain performance in <001>-textured Bi_(0.5)Na_(0.5)TiO_(3)-based ceramics with ergodic relaxor state and core-shell microstructure

Herein,a high strain of ~0.3% with a small hysteresis of 43% is achieved at a low electric field of 4 kV/mm in the highly <001>-textured 0.97(0.76Bi_(0.5)Na_(0.5)TiO_(3)-0.24SrTiO_(3))-0.03NaNbO_(3)(BNT-ST-0.03NN)ceramics with an ergodic relaxor(ER)state,leading to a large normalized strain(d_(33)^(*))of 720 pm/V.The introduction of NN templates into BNT-ST induces the grain orientation growth and enhances the ergodicity.The highly <001>-textured BNT-ST-0.03NN ceramics display a pure ergodic relaxor state with coexisted ferroelectric R3c and antiferroelectric P4bm polar nanoregions(PNRs)on nanoscale.Moreover,due to the incomplete interdiffusion between the NN template and BNT-ST matrix,the textured ceramics present a core-shell structure with the antiferroelectric NN core,and thus the BNT-based matrix owns more R3c PNRs relative to the homogeneous nontextured samples.The high <001> crystallographic texture and more R3c PNRs both facilitate the relaxor-to-ferroelectric transition,leading to the low-field-driven high strain,while the ergodic relaxor state ensures a small hysteresis.Furthermore,the d_(33)^(*)value remains high up to 518 pm/V at 100℃ with an ultra-low hysteresis of 6%.

Ultrahigh energy storage performance realized in AgNbO_(3)-based antiferroelectric materials via multiscale engineering

Antiferroelectric(AFE)materials are promising for the applications in advanced high-power electric and electronic devices.Among them,AgNbO_(3)(AN)-based ceramics have gained considerable attention due to their excellent energy storage performance.Herein,multiscale synergistic modulation is proposed to improve the energy storage performance of AN-based materials,whereby the multilayer structure is employed to improve the breakdown strength(Eb),and Sm/Ta doping is utilized to enhance the AFE stability.As a result,ultrahigh recoverable energy storage density(Wrec)up to 15.0 J·cm^(-3) and energy efficiency of 82.8%are obtained at 1500 kV·cm^(-3) in Sm/Ta co-doped AN multilayer ceramic capacitor(MLCC),which are superior to those of the state-of-the-art AN-based ceramic capacitor.Moreover,the discharge energy density(Wa)in direct-current charge-discharge performance reaches 9.1 J·cm^(-3),which is superior to that of the reported lead-free energy storage systems.The synergistic design of composition and multilayer structure provides an applicable method to optimize the energy storage performance in all dielectric energy storage systems.

Designing silver niobate-based relaxor antiferroelectrics for ultrahigh energy storage performance

AgNbO_(3)(AN)and modified AgNbO_(3) have been extensively investigated as promising lead-free antiferroelectric(AFE)energy storage materials.Previous studies have focused mainly on the use of an ion dopant at the A/B site to obtain a stabilized AFE phase;however,simultaneous improvements in the recoverable energy storage density(Wrec)and efficiency(n)are stll difficult to realize.Herein,we innovatively constructed a AgNbO_(3)-NaNbO_(3)-(Sr_(0.7)Bi_(0.2))TiO_(3)(AN-NN-SBT)ternary solid solution to achieve a relaxor AFE in AgNbO_(3)-based materials.The coexistence of antiferroelectric(M3)and paraelectric(O)phases in 0.8(0.7AgNbO_(3)-0.3NaNbO_(3))-0.2(Sro.7Bio.2)TiO_(3) confirms the successful realization of a relaxor AFE,attributed to multiple ion occupation at the A/B sites.Consequently,a high Wrec of 7.53 J.cm^(-3) and n of 74.0% are acquired,together with superior stability against various temperatures,frequencies,and cycling numbers.Furthermore,a high power density(298.7 MW·cm^(-3))and fast discharge speed(41.4 ns)are also demonstrated for the AgNbO_(3)-based relaxor AFE.This work presents a promising energy storage AgNbO_(3)-based ternary solid solution and proposes a novel strategy for AgNbO_(3)-based energy storage via the design of relaxor AFE materials.

Energy storage properties in Nd-doped AgNbTaO_(3) lead-free antiferroelectric ceramics with Nb-site vacancies

It is crucial to discover lead-free materials with ultrahigh recoverable energy density(Wrec)that can be employed in future pulse power capacitors.In this work,a high Wrec of 4.51 J/cm^(3) was successfully obtained in lead-free Nd-doped AgNb_(0.8)Ta_(0.2)O_(3) antifer­roelectric ceramics at an applied electric field of 290 kV/cm.It is discovered that Nd doping paired with Nb-site vacancies could stabilize the antiferroelectric phase by lowering the temperatures of the M1-M2 and M2-M3 phase transitions,which leads to higher energy storage efficiency.Furthermore,Nd and Ta co-doping will contribute to the electrical homogeneity and low elec­trical conductivity,resulting in large breakdown strengths.Aliovalent doping in Ag-site with Nb-site vacancies serves as a novel strategy for the construction of AgNbO_(3)-based ceramics with excellent energy storage performance.

Energy storage performance and phase transition under high electric field in Na/Ta co-doped AgNbO_(3)ceramics

Lead-free antiferroelectric ceramics with high energy storage performance show great potential in pulsed power capacitors.However,poor breakdown strength and antiferroelectric stability are the two main drawbacks that limit the energy storage performance of antiferroelectric ceramics.Herein,highquality(Ag_(1-x)Na_(x))(Nb_(1-x)Ta_(x))O_(3)ceramics were prepared by the tape casting process.The breakdown strength was greatly improved as a result of the high density and fine grains,while the antiferroelectric stability was enhanced owning to the M2 phase.Benefiting from the synergistic improvement in breakdown strength and antiferroelectric stability,(Ag_(0.80)Na_(0.20))(Nb_(0.80)Ta_(0.20))O_(3)ceramic reveals a benign energy storage performance of W_(rec)=5.8 J/cm^(3)and h=61.7%with good temperature stability,frequency stability and cycling reliability.It is also found that the high applied electric field can promote the M2-M3 phase transition,which may provide ideas to improve the thermal stability of the energy storage performance in AgNbO_(3)-based ceramics.

Enhanced ferroelectricity and magnetism of quenched(1−x)BiFeO3-xBaTiO3 ceramics

Bismuth ferrite(BiFeO3)-based materials are multiferroic materials widely studied.This study reports that strong ferroelectricity and enhanced magnetic performance are simultaneously obtained in the quenched(1−x)BiFeO3−xBaTiO3(BFBT100x,x=0.2 and 0.3)ceramics.Quenching treatment can reduce the amount of defects and Fe2+ions and make the defect dipole in a random state,which is conducive to improving the ferroelectricity and magnetism.Compared with the conventional sintered samples,the quenched ceramics have higher remnant and saturation polarization.As for magnetism,the coercive field(Hc)of the quenched ceramics is smaller and the quenching treatment can increase the maximum magnetization by up to 15%.

Enhanced thermal and cycling reliabilities in (K,Na)(Nb,Sb)O3-CaZr03-(Bi,Na)Hf03 ceramics

The thermal stability and fatigue resistance of piezoelectric ceramics are of great importance for industrialized application.In this study,the electrical properties of(0.99-x)(K0.48Na0.52)Nb0.975Sb0.025)O3-0.01CaZrO3-x(Bi0.5Na0.5)HfO3 ceramics are investigated.When x=0.03,the ceramics exhibit the optimal electrical properties at room temperature and high Curie temperature(Tc=253℃).In addition,the ceramic has outstanding thermal stability(d33≈301 pm/V at 160℃)and fatigue resistance(variation of Pr and d33~10 %after 10^4 electrical cycles).Subsequently,the defect configuration and crystal structure of the ceramics are studied by X-ray diffraction,temperature-dielectric property curves and impedance analysis.On one hand,the doping(Bio sNao.3)HfO3 makes the dielectric constant peaks flatten.On the other hand,the defect concentration and migration are obviously depressed in the doped ceramics.Both of them can enhance the piezoelectrical properties and improve the temperature and cycling reliabilities.The present study reveals that the good piezoelectric properties can be obtained in 0.96(K0.58Na0.52)(Nb0.975Sb.025)O3-0.01CaZrO3-0.03(Bi0.5Na0.5)HfO3 ceramics.

High piezoelectric properties and good temperature stabilities of CuO-modified Ba(Ti_(0.96)Sn_(x)Zr_(0.04-x))O_(3) ceramics

In order to obtain both high piezoelectric property and good temperature stability in BaTiO_(3)-based ceramics in the common usage temperature range,Sn4þand Zr4þare co-doped into BaTiO3 ceramics according to the formula of Ba(Ti_(0.96)Sn_(x)Zr_(0.04-x))O_(3)(BTSZ)(x=0.01-0.4)with 1 mol%CuO being added as sintering-aid in this study.The CuO-modified BTSZ ceramics show both high piezoelectric properties and good temperature stability.Particularly,the CuO-modified Ba(Ti_(0.96)Sn_(x)Zr_(0.04-x))O_(3)ceramic displays the high piezoelectric properties of d_(33)=350 pC/N,k_(p)=49.5%at room-temperature and a weak temperature dependence of kp in the temperature range of
15C and 60C.Moreover,the CuO-modified Ba(Ti_(0.96)Sn_(x)Zr_(0.04-x))O_(3)ceramic shows stable thermal aging behavior with the d33 being almost unchanged until the aging temperature of 100C,which is even higher than its Curie temperature.The high piezoelectric properties of CuO-modified Ba(Ti_(0.96)Sn_(x)Zr_(0.04-x))O_(3)ceramic were ascribed to the dense microstructure with small and uniform grain size distribution.The stable thermal aging behavior can be explained by the aging effect based on the defect dipolar model.

HIGH PIEZOELECTRIC PERFORMANCE AND RELEVANT PHYSICAL MECHANISM OF CuO-MODIFIED Ba(Ti_(0.96)Sn_(0.04))O_(3)CERAMICS

Ba(Ti_(0.96)Sn_(0.04))O_(3)and CuO-modified Ba(Ti_(0.96)Sn_(0.04))O_(3)ceramics were prepared by the solid state reaction technique.Their piezoelectric properties were investigated and compared with those of the recently obtained high-d_(33)BaTiO_(3)ceramic.It has been found that simply substituting Ti4t with Sn4t worsens severely the piezoelectric properties whereas a combined usage of CuO additive greatly improves the overall piezoelectric performance.CuO-modified BaeTi_(0.96)Sn_(0.04)TO_(3)ceramic shows excellent piezoelectric properties of d_(33)=390 pC=N;kp=0.49 and k33=0.67 at room temperature.Furthermore,it possesses weak temperature dependences of electromechanical coe±cients between
20 and 55 and a good thermal aging stability down to a low experimental temperature limit of
50℃and up to 90.Detailed analysis suggests that its high piezoelectric performance should be largely ascribed to the ideal microstructure of high relative density and small grains and the corresponding domain configurations.

Evolution of domain structure in 0.96(K_(0.48)Na_(0.52))(Nb_(0.96)Sb_(0.04))O_(3)0.04(Bi_(0.50)Na_(0.50))ZrO_(3) ceramics with poling and temperature

Domain structure often has significant influences on both piezoelectric properties and piezoelectric temperature stability of a ferroelectric ceramic.In-depth studies on the characters of domain structure should be helpful for the better understanding of piezoelectric performance.In this work,the evolution of domain structure in large-d_(33)0.96(K_(0.48)Na_(0.52))(Nb_(0.96)Sb_(0.04))O_(3)-0.04(Bi_(0.50)Na_(0.50))ZrO_(3) ceramics with poling and temperature was systematically investigated via comparing the various domain patterns that are obtained by acid-etching.It was found that domain structure changes greatly upon poling and varies largely with temperature.Complex domain patterns consisting of long narrow parallel stripes or herringbone structure separated by 180°domain boundaries are observed in the unpoled ceramics at room temperature.Domain patterns become less complicated upon poling,due to the collective polarization reversals of parallel-stripe domain clusters and banded fine-stripe domain segments.Parallel stripes and herringbone bands become much wider upon poling,as some narrow stripes and herringbone bands coalesce into broad ones,respectively.Hierarchical domain structure is commonly seen in the domain patterns acid-etched at room temperature,but is less frequently recognized at elevated temperatures.Schematic models of domain configurations were proposed to explain the domain structure and its evolution with poling.

ZTM陶瓷六方钛铁矿结构热稳定性研究

通过 XRD、DTA、光学显微技术 ,系统研究了 (Zn0 .7Mg0 .3 ) Ti O3 (ZTM)陶瓷六方钛铁矿结构的热稳定性和相分解反应 ,应用传统电子陶瓷工艺制备 ZTM陶瓷。实验发现 ,由于 Zn Ti O3 和Mg Ti O3 生成稳定的固溶体 (Zn,Mg) Ti O3 ,六方钛铁矿相在宽广的烧结温度范围内被稳定 ,但烧结温度超过 1 2 5 0℃ ,六方相 (Zn,Mg) Ti O3 将分解为 (Zn,Mg) 2 Ti O4 和 (Zn,Mg) 2 Ti3 O8,这将会引起瓷体的微破裂和致密度的下降。