Shape memory alloys(SMAs)and shape memory ceramics(SMCs)exhibit high recovery ability due to the martensitic transformation,which complicates the fracture mechanism of SMAs and SMCs.The phase field method,as a powerfu...Shape memory alloys(SMAs)and shape memory ceramics(SMCs)exhibit high recovery ability due to the martensitic transformation,which complicates the fracture mechanism of SMAs and SMCs.The phase field method,as a powerful numerical simulation tool,can efficiently resolve the microstructural evolution,multi-field coupling effects,and fracture behavior of SMAs and SMCs.This review begins by presenting the fundamental theoretical framework of the fracture phase field method as applied to SMAs and SMCs,covering key aspects such as the phase field modeling of martensitic transformation and brittle fracture.Subsequently,it systematically examines the phase field simulations of fracture behaviors in SMAs and SMCs,with particular emphasis on how crystallographic orientation,grain size,and grain boundary properties influence the crack propagation.Additionally,the interplay between martensite transformation and fracture mechanisms is analyzed to provide deeper insights into the material responses under mechanical loading.Finally,the review explores future prospects and emerging trends in phase field simulations of SMA and SMC fracture behavior,along with potential advancements in the fracture phase field method itself,including multi-physics coupling and enhanced computational efficiency for large-scale simulations.展开更多
The dielectric properties and phase transition characteristics of La2O3- and Sb2O3-doped barium strontium titanate ceramics prepared by solid state route were investigated. The microstructure was identified by X-ray d...The dielectric properties and phase transition characteristics of La2O3- and Sb2O3-doped barium strontium titanate ceramics prepared by solid state route were investigated. The microstructure was identified by X-ray diffraction method and scanning electron microscope was also employed to observe the surface morphologies. It is found that （La,Sb）-codoped barium strontium titanate ceramics exhibit typical perovskite structure and the average grain size decreases dramatically with increasing the content of Sb2O3. Both La3＋ ions and Sb3＋ ions occupy the A-sites in perovskite lattice. The dielectric constant and dielectric loss of barium strontium titanate based ceramics are obviously influenced by La2O3 as well as Sb2O3 addition content. The tetragonal-cubic phase transition of La2O3 modified barium strontium titanate ceramics is of second order and the Curie temperature shifts to lower value with increasing the La2O3 doping content. The phase transition of （La,Sb）-codoped barium strontium titanate ceramics diffuses and the deviation from Curie-Weiss law becomes more obvious with the increase in Sb2O3 concentration. The temperature corresponding to the dielectric constant maximum of （La,Sb）-codoped barium strontium titanate ceramics decreases with increasing the Sb2O3 content, which is attributed to the replacement of host ions by the Sb3＋ ions.展开更多
Two types of porcelain tiles with steel slag as the main raw material （steel slag ceramics） were synthesized based on the CaO-A1203-SiO2 and CaO--MgO-SiO2 systems, and their bending strengths up to 53.47 MPa and 99....Two types of porcelain tiles with steel slag as the main raw material （steel slag ceramics） were synthesized based on the CaO-A1203-SiO2 and CaO--MgO-SiO2 systems, and their bending strengths up to 53.47 MPa and 99.84 MPa, respectively, were obtained. The presence of anorthite, a-quartz, magnetite, and pyroxene crystals （augite and diopside） in the steel slag ceramics were very different from the composition of traditional ceramics. X-ray diffraction （XRD） and electron probe X-ray microanalysis （EPMA） results illustrated that the addition of steel slag reduced the temperature of extensive liquid generation and further decreased the firing temperature. The considerable contents of glass-modifying oxide liquids with rather low viscosities at high temperature in the steel slag ceramic adobes promoted element diffusion and crystallization. The results of this study demonstrated a new approach for extensive and effective recycling of steel slag.展开更多
1. Introduction The requirements for the performance of materials have become increasingly stringent in recent years, with the rapid development of aerospace, machinery, metallurgy, nuclear energy,chemical industry, a...1. Introduction The requirements for the performance of materials have become increasingly stringent in recent years, with the rapid development of aerospace, machinery, metallurgy, nuclear energy,chemical industry, and military industry [1,2], and traditional single-phase materials are gradually revealing disadvantages due to the contradiction between demanding service environments and simple material design.展开更多
Porous bismuth ferrite ceramics were synthesized by sacrificial pore former method. A mixture of BiFeO3 and 20 wt% of various pore formers including high density polyethylene, polyethylene glycol, polyvinyl alcohol, u...Porous bismuth ferrite ceramics were synthesized by sacrificial pore former method. A mixture of BiFeO3 and 20 wt% of various pore formers including high density polyethylene, polyethylene glycol, polyvinyl alcohol, urea and graphite was intensively milled for 10 h in a planetary ball mill, uniaxially cold pressed and then subjected to the multi-stage heat treatment. The results revealed that urea and polyvinyl alcohol are appropriate candidates for maintaining the strength of the final porous structure. Density and porosity measurements showed that by employing 20 wt% of high density polyethylene and graphite, a porous sample with a maximum porosity of nearly 40% could be obtained. Mercury porosimetry results showed that using urea as a pore former gives porous bismuth ferrite with a mean pore diameter of 7μm, uniform pore distribution as well as interconnected pores. Moreover, reactions between BiFeO3 matrix phase and thermal decomposition products of pore formers can lead to degradation of the BiFeO3 phase in the final porous samples. Analysis of X-ray diffraction patterns illustrated that in the samples pro- cessed with graphite, high density polyethylene and polyvinyl alcohol as pore former, BiFeO3 matrix phase partially or completely decomposed to intermediate phases of Bi2Fe4O9 and Bi25FeO40. Using of urea did not damage the matrix phase and porous BiFeO3 within the original perovskite structure could be prepared. Furthermore, thermodynamic investigation was carried out for prediction of possible in- teractions between matrix phase and pore former at elevated temperatures.展开更多
Antiferroelectric ferroelectric （AFE-FE） phase transition in ceramic Pbo.97Lao.02（Zro.75Snon36Tion14）O3 （PLZST） was studied by dielectric spectroscopy as functions of frequency （102-105 Hz） and pressure （0-50...Antiferroelectric ferroelectric （AFE-FE） phase transition in ceramic Pbo.97Lao.02（Zro.75Snon36Tion14）O3 （PLZST） was studied by dielectric spectroscopy as functions of frequency （102-105 Hz） and pressure （0-500 MPa） under a DC electric field. The hydrostatic pressure-dependent remnant polarization and dielectric constant were mea- sured. The results show that remnant polarization of the metastable rhombohedral ferroelectric PLZST poled ceramic decreases sharply and depoles completely at phase transition under hydrostatic pressure. The dielectric constant um dergoes an abrupt jump twice during a load and unload cycle under an electric field. The two abrupt jumps correspond to two phase transitions, FE AFE and AFE-FE.展开更多
To make the ferroelectric BaTiO3 possess ferromagnetism simultaneously,magnetic Fe was doped into BaTiO3 ceramics at doping levels up to 10%(molar fraction).Both tetragonal and hexagonal phases coexisted in the Fe-dop...To make the ferroelectric BaTiO3 possess ferromagnetism simultaneously,magnetic Fe was doped into BaTiO3 ceramics at doping levels up to 10%(molar fraction).Both tetragonal and hexagonal phases coexisted in the Fe-doped BaTiO3 ceramics except at 1% doping level.X-ray diffraction analysis indicated that higher doping level of Fe,higher sintering temperature and longer sintering time promoted the formation of hexagonal phases in Fe-doped BaTiO3 ceramics.Ferroelectricity was observed in all samples at room temperature,but it was greatly depressed by Fe doping.Except at doping level of 1%,room-temperature ferromagnetism was observed in the BaTiO3 ceramics.The dependence of the saturation magnetization and coercivities of the Fe-doped BaTiO3 ceramics on doping level was systematically studied.Both the saturation magnetization and magnetic coercivities were found to be dependent on the doping level as well as the fraction of the hexagonal phase in the ceramics.展开更多
Piezoelectric ceramic materials are important components of piezoelectric buzzers,where the parameter of inverse piezoelectric coefficient(d_(33)^(*))plays a decisive role in the performance of the buzzer.Here,we repo...Piezoelectric ceramic materials are important components of piezoelectric buzzers,where the parameter of inverse piezoelectric coefficient(d_(33)^(*))plays a decisive role in the performance of the buzzer.Here,we report the manufacture and performance of a lead-free ceramic-based(0.96(K_(0.5)Na_(0.5))(Nb_(0.96)Sb_(0.04))O_(3)-0.04(Bi_(0.5)Na_(0.5))ZrO_(3)-1 mol%Al_(2)O_(3),abbreviated as KNNS-BNZ-1 mol%Al_(2)O_(3))piezoelectric buzzer and compare it with commercial(PbZr_(0.5)Ti_(0.5)O_(3),abbreviated as PZT)ceramics.Briefly,KNN-based ceramics have a typical perovskite structure and piezoelectric properties of d_(33)=480 pC/N,k_(p)=0.62 and d_(33)^(*)=830 pm/V,compared to d_(33)=500 pC/N,k_(p)=0.6 and d_(33)^(*)=918 pm/V of the commercial PZT-4 ceramics.Our results show that the KNNS-BNZ-1 mol%Al_(2)O_(3)ceramics have a similar sound pressure level performance over the testing frequency range to commercial PZT ceramics(which is even better in the 3-4 kHz range).These findings highlight the great application potential of KNN-based piezoelectric ceramics.展开更多
As a kind of rare materials,nano-silver has broad application prospects in the fields of catalysis,medical treatment,new energy and so on.However,there are few reports on the systematic research of nano-silver in cera...As a kind of rare materials,nano-silver has broad application prospects in the fields of catalysis,medical treatment,new energy and so on.However,there are few reports on the systematic research of nano-silver in ceramic glazes.In this work,different color ceramic glazes were produced by tuning the nano-silver content and optimizing the firing process.The crystalline phase composition,micro-morphology and elemental distribution of fired glazes were analyzed and discussed in depth.The elemental composition and distribution of the samples were studied.The surface of the glazes with varying Ag contents fired under the reducing atmosphere exhibited blue-white.And the blue color is attributable to Rayleigh scattering that may arise because the phase-separation structures existed in glazes.Interestingly,the color of the ceramic glazes with varying Ag contents changed to golden-yellow when the ceramic glazes were fired under the air atmosphere.Golden-yellow color of the samples fired under the air atmosphere is mainly attributable to the silver nanoparticles,though Ag^(+) may be existed in the glazes.展开更多
In this paper, by using the level spectroscopy method and bosonization theory, we discuss the evolution of the bond-order-wave （BOW） phase in a one-dimensional half-filled extended Hubbard model wlth the on-site Cou...In this paper, by using the level spectroscopy method and bosonization theory, we discuss the evolution of the bond-order-wave （BOW） phase in a one-dimensional half-filled extended Hubbard model wlth the on-site Coulomb repulsion U as well as the inter-site Coulomb repulsion V and antiferromagnetic exchange J. After clarifying the generic phase diagrams in three limiting cases with one of the parameters being fixed at zero individually, we find that the BOW phase in the U-V phase diagram is initially enlarged as J increases from zero but is eventually suppressed as J increases further in the strong-coupling regime. A three-dimensional phase diagram is suggested where the BOW phase exists in an extended region separated from the spin-density-wave and charge-density-wave phases.展开更多
Li/Sb-doped (Na,K)NbO3 with a nominal composition of [Li0.05(Na0.535K0.48)0.95](Nb0.94Sb0.06)O3 ceramic was synthesized by normal sintering. The phase structure, microstructure, and electrical properties were investig...Li/Sb-doped (Na,K)NbO3 with a nominal composition of [Li0.05(Na0.535K0.48)0.95](Nb0.94Sb0.06)O3 ceramic was synthesized by normal sintering. The phase structure, microstructure, and electrical properties were investigated with a special emphasis on the influence of the sintering temperature. A polymorphic phase transition (PPT) from orthorhombic to tetragonal symmetry was observed when the sintering temperature was raised from 1040 to 1050 ℃, whereby the piezoelectric coefficient d33 and the electromechanical coupling coefficient kp reached the peak values of 245 pC·N-1 and 41.2%, respectively. The PPT induced by varying the sintering temperature is due to the different volatilization extents of alkali metals and appears to a lower sintering temperature with increasing Li content. The trace modifying of alkali metal content is more effective than doping B site element to enhance the d33 value.展开更多
MgO-modified Li0.06（Na0.5K0.5）0.94NbO3O3 （L6NKN） lead-free piezoelectric ceramics were synthesized by normal sintering at a rela- tively low temperature of 1000℃. The crystalline phase, microstructure, and electr...MgO-modified Li0.06（Na0.5K0.5）0.94NbO3O3 （L6NKN） lead-free piezoelectric ceramics were synthesized by normal sintering at a rela- tively low temperature of 1000℃. The crystalline phase, microstructure, and electrical properties of the ceramics were investigated with a special emphasis on the influence of MgO content. The addition of MgO effectively improves the sintembility of the L6NKN ceramics. X-my diffr cfion analysis indicates that the morphotropic phase boundary （MPB） separating orthorhombic and tetragonal phases for the ceramics lies in the range of Mg doping content （x） from 0.3at% to 0.7at%. High electrical properties of the piezoelectric constant （d33=238 pC/N）, planar electromechanical coupling coefficient （kp=41.5%）, relative dielectric constant （εr=905）, and remanent polarization （Pr=38.3 μC/cm2） are obtained from the specimen with x=0.5at%, which suggests that the Li0.06（Na0.5K0.5）0.94Nb（1-2x/5）MgxO3 （x=0.5at%） ceramic is a promising lead-free piezoelectric material.展开更多
In situ formed low density O＇-sialon-based multiphase ceramics were prepared by liquid-phase sintering method at 1400°C with Si3N4, SiO2 and Al2O3 as raw materials.Crystalline phases were identified by X-ray dif...In situ formed low density O＇-sialon-based multiphase ceramics were prepared by liquid-phase sintering method at 1400°C with Si3N4, SiO2 and Al2O3 as raw materials.Crystalline phases were identified by X-ray diffraction（XRD）.The quantitative phase analysis was finished by matrix-flushing method and the substitution parameter x value of O＇-sialon was estimated.The effects of sintering additives on the phase composition of the material were studied.The results show that, when using Y2O3 alone, Al6Si2O13 phase can be formed in the material, but when using Y2O3 and MgO, MgAl2O4 phase can be preferentially formed and the Al6Si2O13 is not observed.The mechanical properties of the material were measured and the relationships between microstructure and mechanical properties were discussed.The sample with Y2O3 and MgO sintering additives, using fused quartz alone as SiO2 source, displays a combination of high bending strength（163 MPa） and good fracture toughness（3.11 MPa·m1/2）.Bending strength and fracture toughness of the samples increase with the increase of the content and aspect ratio of elongated grains and decrease with the increase of the porosity.展开更多
Lead-free piezoelectric NaxK1-xNbO3（x = 0.3-0.8）（NKN） ceramics were fabricated by normal sintering at 1060°C for 2 h.Microstructures and electrical properties of the ceramics were investigated with a special ...Lead-free piezoelectric NaxK1-xNbO3（x = 0.3-0.8）（NKN） ceramics were fabricated by normal sintering at 1060°C for 2 h.Microstructures and electrical properties of the ceramics were investigated with a special emphasis on the influence of Na content.The grain size of the produced dense ceramic was decreased by increasing Na content.A discontinuous change in the space distance was found at the composition close to Na0.7K0.3NbO3 ceramic, which indicates the presence of a transitional composition between two different orthorhombic phases, which is similar to the behavior of morphotropic phase boundary（MPB） in NaxK1-xNbO3 ceramics.Such MPB-like behavior contributes to the enhanced piezoelectric coefficient d33 of 122 pC/N, planar-mode electromechanical coupling coefficient kP of 28.6%, and dielectric constant εr of 703, respectively for the Na0.7K0.3NbO3 ceramic.Cubic temperature TC and the transitional temperature TO-T from orthorhombic to tetragonal phase are observed at around 420°C and 200°C, respectively.展开更多
The aim of this study is to investigate CO2 two-phase nozzle flow in terms of both experimental and analytical aspects for the optimum design of two-phase flow nozzle of CO2 two-phase flow ejector. In the experiment, ...The aim of this study is to investigate CO2 two-phase nozzle flow in terms of both experimental and analytical aspects for the optimum design of two-phase flow nozzle of CO2 two-phase flow ejector. In the experiment, it is measured that the temperature profile in the stream-wise direction of a divergent-convergent nozzle through which CO2 in the supercritical pressure condition is blown down into the atmosphere. In the analysis, a one-dimensional model which assumes steady, adiabatic, frictionless, and equilibrium is proposed. In the convergent part of the nozzle the flow is treated as single-phase flow of liquid, whereas in the divergent part the flow is treated as separated two-phase flow with saturated condition. The analytical results indicate that the temperature and the pressure decrease rapidly in the divergent part, and the void fraction increases immediately near the throat. Although this analysis is quite simple, the analytical results can follow the experimental results well within this study.展开更多
Adjustable or programmable metamaterials offer versatile functions,while the complex multi-dimensional regulation increases workload,and hinders their applications in practical scenarios.To address these challenges,we...Adjustable or programmable metamaterials offer versatile functions,while the complex multi-dimensional regulation increases workload,and hinders their applications in practical scenarios.To address these challenges,we present a mechanically programmable acoustic metamaterial for real-time focal tuning via one-dimensional phase-gradient modulation in this paper.The device integrates a phase gradient structure with concave cavity channels and an x-shaped telescopic mechanical framework,enabling dynamic adjustment of inter-unit spacing(1 mm-3 mm)through a microcontroller-driven motor.By modulating the spacing between adjacent channels,the phase gradient is precisely controlled,allowing continuous focal shift from 50 mm to 300 mm along the x-axis at 7500 Hz.Broadband focusing is also discussed in the range6800 Hz-8100 Hz,with transmission coefficients exceeding 0.5,ensuring high efficiency and robust performance.Experimental results align closely with simulations,validating the design's effectiveness and adaptability.Unlike conventional programmable metamaterials requiring multi-dimensional parameter optimization,this approach simplifies real-time control through single-axis mechanical adjustment,significantly reducing operational complexity.Due to the advantages of broadband focusing,simple control mode,real-time monitoring,and so on,the device may have extensive applications in the fields of acoustic imaging,nondestructive testing,ultrasound medical treatment,etc.展开更多
In this work,the rare-earth doped ternary lead zirconate titanate ceramics with chemical formula of[0.3 Pb(Zn_(1/3)Nb_(2/3))O_(3)-0.7Pb(Zr_(0.52)Ti_(0.48))O_(3)]+x wt%CeO_(2)(x=0-0.5,abbreviated as 0.3PZN-0.7PZT-xCe)w...In this work,the rare-earth doped ternary lead zirconate titanate ceramics with chemical formula of[0.3 Pb(Zn_(1/3)Nb_(2/3))O_(3)-0.7Pb(Zr_(0.52)Ti_(0.48))O_(3)]+x wt%CeO_(2)(x=0-0.5,abbreviated as 0.3PZN-0.7PZT-xCe)were synthesized by a conventional solid-state reaction route,specific attentions was focused on the effects of CeO_(2)dopants on the structures and electrical properties of the 0.3PZN-0.7PZT ceramics,revealing the role conve rsion of CeO_(2)dopants with its doping amount(x).When less CeO_(2)(x≤0.2)is introduced into 0.3PZN-0.7PZT,the prepared ceramics are identified as the coexistence of rhombohedral and tetragonal phases,also involved with an increased grain size and a reduced atomic ratio of Pb/(Zr+Ti+Zn+Nb).The increased remanent polarization(Pr)and deceased coercive filed(Ec),as well as improved dielectric permittivity(er)and piezoelectric coefficient(d_(33))de monstrate the donor substitution of Ce^(3+)for Pb^(2+)at the A-site of perovskite lattice.Conversely,the introduction of excessive CeO_(2)(x>0.2)causes a reversal evolution in the electrical properties of ceramics,suggesting that some of the introduced cerium element tends to become Ce4+,which equivalently substitutes for Zr^(4+)at the B-site.Additionally,the diffused phase transition(DPT)behaviors of the 0.3PZN-0.7PZT-xCe ceramics were investigated by the modified Curie-Weiss Law.The sample with x=0.2 shows reduced DPT character and optimized electrical properties,including TC=297℃,εr=1400,d_(33)=480 pC/N,tanδ=1.6%,kp=65%,d_(33)·g_(33)=16.32×10^(-12)m^(2)/N,Pr=38.3μC/cm^(2)and Ec=1.02 kV/mm.These enhanced electrical properties not only are contributed by the donor substitution effect of Ce^(3+),but also benefit from the optimized morphotropic phase boundary that is close to the tetragonal-rich side.展开更多
The phase transitions, dielectric properties, and polarization versus electric field （P-E） hysteresis loops of Pbo.97Lao.02（Zr0.42Sn0.58-xTix）O3 （0.13≤ x ≤0.18） （PLZST） bulk ceramics were systematically inve...The phase transitions, dielectric properties, and polarization versus electric field （P-E） hysteresis loops of Pbo.97Lao.02（Zr0.42Sn0.58-xTix）O3 （0.13≤ x ≤0.18） （PLZST） bulk ceramics were systematically investigated. This study exhibited a sequence of phase transitions by analyzing the change of the P-E hysteresis loops with increasing temperature. The anfiferroelectric （AFE） to ferroelectric （FE） phase boundary of PLZST with the Zr content of 0.42 was found to locate at the Ti content between 0.14 and 0.15. This work is aimed to improve the ternary phase diagram of lanthanum-doped PZST with the Zr content of 0.42 and will be a good reference for seeking high energy storage density in the PLZST system with low-Zr content.展开更多
The brazing of Al 2O 3 to Nb was achieved by the method of transient liquid phase (TLP) bonding. Ti foil and Ni 5V alloy foil were used as interlayers for the bonding. The base materials were brazed at 1 4231 573 K fo...The brazing of Al 2O 3 to Nb was achieved by the method of transient liquid phase (TLP) bonding. Ti foil and Ni 5V alloy foil were used as interlayers for the bonding. The base materials were brazed at 1 4231 573 K for 1120 min. The results show that the shear strength of the joint first increases and then decreases with increasing holding time and brazing temperature. The joint interface microstructure and elements distribution were investigated. It can be concluded that a composite structure, in which the base metals are solid solution Nb(V) and Nb(Ti) reinforced by Ni 2Ti, is formed when the brazing temperature is 1 473 K and holding time 15 min, and a satisfactory joint strength can be achieved. The interaction of Ti foil and Ni 5V foil leads to the formation of liquid eutectic phase with low melting point, at the same time the combination of Ti come from the interlayer with O atoms from Al 2O 3 results in the bonding of Al 2O 3 and Nb.展开更多
Dielectric materials are essential in modern electronics,serving as the backbone of numerous components across a wide array of electronic devices[1,2].As technology advances,the demand for materials with high permitti...Dielectric materials are essential in modern electronics,serving as the backbone of numerous components across a wide array of electronic devices[1,2].As technology advances,the demand for materials with high permittivity,low dielectric loss,and thermal stability continues to rise.Traditional strategies to enhance permittivity often involve mechanisms such as phase transitions in ferroelectrics or interfacial polarization in boundary layer capacitor(IBLC)systems.However,each comes with trade-offs.展开更多
基金supported by the National Natural Science Foundation of China(12202294)the Sichuan Science and Technology Program(2024NSFSC1346).
文摘Shape memory alloys(SMAs)and shape memory ceramics(SMCs)exhibit high recovery ability due to the martensitic transformation,which complicates the fracture mechanism of SMAs and SMCs.The phase field method,as a powerful numerical simulation tool,can efficiently resolve the microstructural evolution,multi-field coupling effects,and fracture behavior of SMAs and SMCs.This review begins by presenting the fundamental theoretical framework of the fracture phase field method as applied to SMAs and SMCs,covering key aspects such as the phase field modeling of martensitic transformation and brittle fracture.Subsequently,it systematically examines the phase field simulations of fracture behaviors in SMAs and SMCs,with particular emphasis on how crystallographic orientation,grain size,and grain boundary properties influence the crack propagation.Additionally,the interplay between martensite transformation and fracture mechanisms is analyzed to provide deeper insights into the material responses under mechanical loading.Finally,the review explores future prospects and emerging trends in phase field simulations of SMA and SMC fracture behavior,along with potential advancements in the fracture phase field method itself,including multi-physics coupling and enhanced computational efficiency for large-scale simulations.
基金Project (11KJB430007) supported by the University Natural Science Research Program of Jiangsu Province, ChinaProject supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions, China
文摘The dielectric properties and phase transition characteristics of La2O3- and Sb2O3-doped barium strontium titanate ceramics prepared by solid state route were investigated. The microstructure was identified by X-ray diffraction method and scanning electron microscope was also employed to observe the surface morphologies. It is found that （La,Sb）-codoped barium strontium titanate ceramics exhibit typical perovskite structure and the average grain size decreases dramatically with increasing the content of Sb2O3. Both La3＋ ions and Sb3＋ ions occupy the A-sites in perovskite lattice. The dielectric constant and dielectric loss of barium strontium titanate based ceramics are obviously influenced by La2O3 as well as Sb2O3 addition content. The tetragonal-cubic phase transition of La2O3 modified barium strontium titanate ceramics is of second order and the Curie temperature shifts to lower value with increasing the La2O3 doping content. The phase transition of （La,Sb）-codoped barium strontium titanate ceramics diffuses and the deviation from Curie-Weiss law becomes more obvious with the increase in Sb2O3 concentration. The temperature corresponding to the dielectric constant maximum of （La,Sb）-codoped barium strontium titanate ceramics decreases with increasing the Sb2O3 content, which is attributed to the replacement of host ions by the Sb3＋ ions.
文摘Two types of porcelain tiles with steel slag as the main raw material （steel slag ceramics） were synthesized based on the CaO-A1203-SiO2 and CaO--MgO-SiO2 systems, and their bending strengths up to 53.47 MPa and 99.84 MPa, respectively, were obtained. The presence of anorthite, a-quartz, magnetite, and pyroxene crystals （augite and diopside） in the steel slag ceramics were very different from the composition of traditional ceramics. X-ray diffraction （XRD） and electron probe X-ray microanalysis （EPMA） results illustrated that the addition of steel slag reduced the temperature of extensive liquid generation and further decreased the firing temperature. The considerable contents of glass-modifying oxide liquids with rather low viscosities at high temperature in the steel slag ceramic adobes promoted element diffusion and crystallization. The results of this study demonstrated a new approach for extensive and effective recycling of steel slag.
基金financially supported by the National Natural Science Foundation of China(Nos.51872061,52032002,51972081)Heilongjiang Touyan Team Program。
文摘1. Introduction The requirements for the performance of materials have become increasingly stringent in recent years, with the rapid development of aerospace, machinery, metallurgy, nuclear energy,chemical industry, and military industry [1,2], and traditional single-phase materials are gradually revealing disadvantages due to the contradiction between demanding service environments and simple material design.
基金financial supports of this work by the University of Tehran and Iran Nanotechnology Initiative Council
文摘Porous bismuth ferrite ceramics were synthesized by sacrificial pore former method. A mixture of BiFeO3 and 20 wt% of various pore formers including high density polyethylene, polyethylene glycol, polyvinyl alcohol, urea and graphite was intensively milled for 10 h in a planetary ball mill, uniaxially cold pressed and then subjected to the multi-stage heat treatment. The results revealed that urea and polyvinyl alcohol are appropriate candidates for maintaining the strength of the final porous structure. Density and porosity measurements showed that by employing 20 wt% of high density polyethylene and graphite, a porous sample with a maximum porosity of nearly 40% could be obtained. Mercury porosimetry results showed that using urea as a pore former gives porous bismuth ferrite with a mean pore diameter of 7μm, uniform pore distribution as well as interconnected pores. Moreover, reactions between BiFeO3 matrix phase and thermal decomposition products of pore formers can lead to degradation of the BiFeO3 phase in the final porous samples. Analysis of X-ray diffraction patterns illustrated that in the samples pro- cessed with graphite, high density polyethylene and polyvinyl alcohol as pore former, BiFeO3 matrix phase partially or completely decomposed to intermediate phases of Bi2Fe4O9 and Bi25FeO40. Using of urea did not damage the matrix phase and porous BiFeO3 within the original perovskite structure could be prepared. Furthermore, thermodynamic investigation was carried out for prediction of possible in- teractions between matrix phase and pore former at elevated temperatures.
基金Project supported by the National Basic Research Program of China (Grant No.2009CB623306)the International Science & Technology Cooperation Program of China (Grant No.2010DFR50480)the National Natural Science Foundation of China (Grant No.10976022)
文摘Antiferroelectric ferroelectric （AFE-FE） phase transition in ceramic Pbo.97Lao.02（Zro.75Snon36Tion14）O3 （PLZST） was studied by dielectric spectroscopy as functions of frequency （102-105 Hz） and pressure （0-500 MPa） under a DC electric field. The hydrostatic pressure-dependent remnant polarization and dielectric constant were mea- sured. The results show that remnant polarization of the metastable rhombohedral ferroelectric PLZST poled ceramic decreases sharply and depoles completely at phase transition under hydrostatic pressure. The dielectric constant um dergoes an abrupt jump twice during a load and unload cycle under an electric field. The two abrupt jumps correspond to two phase transitions, FE AFE and AFE-FE.
基金Project(60661001) supported by the National Natural Science Foundation of China
文摘To make the ferroelectric BaTiO3 possess ferromagnetism simultaneously,magnetic Fe was doped into BaTiO3 ceramics at doping levels up to 10%(molar fraction).Both tetragonal and hexagonal phases coexisted in the Fe-doped BaTiO3 ceramics except at 1% doping level.X-ray diffraction analysis indicated that higher doping level of Fe,higher sintering temperature and longer sintering time promoted the formation of hexagonal phases in Fe-doped BaTiO3 ceramics.Ferroelectricity was observed in all samples at room temperature,but it was greatly depressed by Fe doping.Except at doping level of 1%,room-temperature ferromagnetism was observed in the BaTiO3 ceramics.The dependence of the saturation magnetization and coercivities of the Fe-doped BaTiO3 ceramics on doping level was systematically studied.Both the saturation magnetization and magnetic coercivities were found to be dependent on the doping level as well as the fraction of the hexagonal phase in the ceramics.
基金Project supported by the Key Research and Develop Projects in Gansu Province(Grant No.23YFGA0002)the project funding of Audiowell Electronics(Guangdong)Co.,Ltd.
文摘Piezoelectric ceramic materials are important components of piezoelectric buzzers,where the parameter of inverse piezoelectric coefficient(d_(33)^(*))plays a decisive role in the performance of the buzzer.Here,we report the manufacture and performance of a lead-free ceramic-based(0.96(K_(0.5)Na_(0.5))(Nb_(0.96)Sb_(0.04))O_(3)-0.04(Bi_(0.5)Na_(0.5))ZrO_(3)-1 mol%Al_(2)O_(3),abbreviated as KNNS-BNZ-1 mol%Al_(2)O_(3))piezoelectric buzzer and compare it with commercial(PbZr_(0.5)Ti_(0.5)O_(3),abbreviated as PZT)ceramics.Briefly,KNN-based ceramics have a typical perovskite structure and piezoelectric properties of d_(33)=480 pC/N,k_(p)=0.62 and d_(33)^(*)=830 pm/V,compared to d_(33)=500 pC/N,k_(p)=0.6 and d_(33)^(*)=918 pm/V of the commercial PZT-4 ceramics.Our results show that the KNNS-BNZ-1 mol%Al_(2)O_(3)ceramics have a similar sound pressure level performance over the testing frequency range to commercial PZT ceramics(which is even better in the 3-4 kHz range).These findings highlight the great application potential of KNN-based piezoelectric ceramics.
基金financially supported by the National Natural Science Foundation of China(Grant No.52072327)Zhongyuan Thousand Talents(Zhongyuan Scholars)Program of Henan Province(No.202101510004)+2 种基金the Scientific and Technological Projects of Henan Province(No.202102210022)the Undergraduate Innovation and Entrepreneurship Project of Henan Province(No.202010480011)Henan Province Water Conservancy Technology Project(No.GG201922)。
文摘As a kind of rare materials,nano-silver has broad application prospects in the fields of catalysis,medical treatment,new energy and so on.However,there are few reports on the systematic research of nano-silver in ceramic glazes.In this work,different color ceramic glazes were produced by tuning the nano-silver content and optimizing the firing process.The crystalline phase composition,micro-morphology and elemental distribution of fired glazes were analyzed and discussed in depth.The elemental composition and distribution of the samples were studied.The surface of the glazes with varying Ag contents fired under the reducing atmosphere exhibited blue-white.And the blue color is attributable to Rayleigh scattering that may arise because the phase-separation structures existed in glazes.Interestingly,the color of the ceramic glazes with varying Ag contents changed to golden-yellow when the ceramic glazes were fired under the air atmosphere.Golden-yellow color of the samples fired under the air atmosphere is mainly attributable to the silver nanoparticles,though Ag^(+) may be existed in the glazes.
基金The project supported in part by National Natural Science Foundation of China and the Natural Science Foundation of Zhejiang Province of China. We acknowledge useful discussions with X. Feng, T. Xiang, and Y. Yu.
文摘In this paper, by using the level spectroscopy method and bosonization theory, we discuss the evolution of the bond-order-wave （BOW） phase in a one-dimensional half-filled extended Hubbard model wlth the on-site Coulomb repulsion U as well as the inter-site Coulomb repulsion V and antiferromagnetic exchange J. After clarifying the generic phase diagrams in three limiting cases with one of the parameters being fixed at zero individually, we find that the BOW phase in the U-V phase diagram is initially enlarged as J increases from zero but is eventually suppressed as J increases further in the strong-coupling regime. A three-dimensional phase diagram is suggested where the BOW phase exists in an extended region separated from the spin-density-wave and charge-density-wave phases.
基金financially supported by the Specialized Research Fund for the Doctoral Program of Higher Education of China(No.20090006110010)Beijing Natural Science Foundation(No.2112028)
文摘Li/Sb-doped (Na,K)NbO3 with a nominal composition of [Li0.05(Na0.535K0.48)0.95](Nb0.94Sb0.06)O3 ceramic was synthesized by normal sintering. The phase structure, microstructure, and electrical properties were investigated with a special emphasis on the influence of the sintering temperature. A polymorphic phase transition (PPT) from orthorhombic to tetragonal symmetry was observed when the sintering temperature was raised from 1040 to 1050 ℃, whereby the piezoelectric coefficient d33 and the electromechanical coupling coefficient kp reached the peak values of 245 pC·N-1 and 41.2%, respectively. The PPT induced by varying the sintering temperature is due to the different volatilization extents of alkali metals and appears to a lower sintering temperature with increasing Li content. The trace modifying of alkali metal content is more effective than doping B site element to enhance the d33 value.
基金supported by the Research Fund for the Doctoral Program of Higher Education of China (No20090006110010)the National Basic Research Priorities Program of China (No2007CB613301)the Program of University-Industry Cooperation Supported by the Ministry of Education and Guangdong Province of China (No2008B090500262)
文摘MgO-modified Li0.06（Na0.5K0.5）0.94NbO3O3 （L6NKN） lead-free piezoelectric ceramics were synthesized by normal sintering at a rela- tively low temperature of 1000℃. The crystalline phase, microstructure, and electrical properties of the ceramics were investigated with a special emphasis on the influence of MgO content. The addition of MgO effectively improves the sintembility of the L6NKN ceramics. X-my diffr cfion analysis indicates that the morphotropic phase boundary （MPB） separating orthorhombic and tetragonal phases for the ceramics lies in the range of Mg doping content （x） from 0.3at% to 0.7at%. High electrical properties of the piezoelectric constant （d33=238 pC/N）, planar electromechanical coupling coefficient （kp=41.5%）, relative dielectric constant （εr=905）, and remanent polarization （Pr=38.3 μC/cm2） are obtained from the specimen with x=0.5at%, which suggests that the Li0.06（Na0.5K0.5）0.94Nb（1-2x/5）MgxO3 （x=0.5at%） ceramic is a promising lead-free piezoelectric material.
文摘In situ formed low density O＇-sialon-based multiphase ceramics were prepared by liquid-phase sintering method at 1400°C with Si3N4, SiO2 and Al2O3 as raw materials.Crystalline phases were identified by X-ray diffraction（XRD）.The quantitative phase analysis was finished by matrix-flushing method and the substitution parameter x value of O＇-sialon was estimated.The effects of sintering additives on the phase composition of the material were studied.The results show that, when using Y2O3 alone, Al6Si2O13 phase can be formed in the material, but when using Y2O3 and MgO, MgAl2O4 phase can be preferentially formed and the Al6Si2O13 is not observed.The mechanical properties of the material were measured and the relationships between microstructure and mechanical properties were discussed.The sample with Y2O3 and MgO sintering additives, using fused quartz alone as SiO2 source, displays a combination of high bending strength（163 MPa） and good fracture toughness（3.11 MPa·m1/2）.Bending strength and fracture toughness of the samples increase with the increase of the content and aspect ratio of elongated grains and decrease with the increase of the porosity.
基金supported by the National Natural Science Foundation of China (No. 50842028)the National Basic Research Priorities Program of China (No. 2007CB613301)
文摘Lead-free piezoelectric NaxK1-xNbO3（x = 0.3-0.8）（NKN） ceramics were fabricated by normal sintering at 1060°C for 2 h.Microstructures and electrical properties of the ceramics were investigated with a special emphasis on the influence of Na content.The grain size of the produced dense ceramic was decreased by increasing Na content.A discontinuous change in the space distance was found at the composition close to Na0.7K0.3NbO3 ceramic, which indicates the presence of a transitional composition between two different orthorhombic phases, which is similar to the behavior of morphotropic phase boundary（MPB） in NaxK1-xNbO3 ceramics.Such MPB-like behavior contributes to the enhanced piezoelectric coefficient d33 of 122 pC/N, planar-mode electromechanical coupling coefficient kP of 28.6%, and dielectric constant εr of 703, respectively for the Na0.7K0.3NbO3 ceramic.Cubic temperature TC and the transitional temperature TO-T from orthorhombic to tetragonal phase are observed at around 420°C and 200°C, respectively.
文摘The aim of this study is to investigate CO2 two-phase nozzle flow in terms of both experimental and analytical aspects for the optimum design of two-phase flow nozzle of CO2 two-phase flow ejector. In the experiment, it is measured that the temperature profile in the stream-wise direction of a divergent-convergent nozzle through which CO2 in the supercritical pressure condition is blown down into the atmosphere. In the analysis, a one-dimensional model which assumes steady, adiabatic, frictionless, and equilibrium is proposed. In the convergent part of the nozzle the flow is treated as single-phase flow of liquid, whereas in the divergent part the flow is treated as separated two-phase flow with saturated condition. The analytical results indicate that the temperature and the pressure decrease rapidly in the divergent part, and the void fraction increases immediately near the throat. Although this analysis is quite simple, the analytical results can follow the experimental results well within this study.
基金supported by the National Natural Science Foundation of China(Grant No.12374416)。
文摘Adjustable or programmable metamaterials offer versatile functions,while the complex multi-dimensional regulation increases workload,and hinders their applications in practical scenarios.To address these challenges,we present a mechanically programmable acoustic metamaterial for real-time focal tuning via one-dimensional phase-gradient modulation in this paper.The device integrates a phase gradient structure with concave cavity channels and an x-shaped telescopic mechanical framework,enabling dynamic adjustment of inter-unit spacing(1 mm-3 mm)through a microcontroller-driven motor.By modulating the spacing between adjacent channels,the phase gradient is precisely controlled,allowing continuous focal shift from 50 mm to 300 mm along the x-axis at 7500 Hz.Broadband focusing is also discussed in the range6800 Hz-8100 Hz,with transmission coefficients exceeding 0.5,ensuring high efficiency and robust performance.Experimental results align closely with simulations,validating the design's effectiveness and adaptability.Unlike conventional programmable metamaterials requiring multi-dimensional parameter optimization,this approach simplifies real-time control through single-axis mechanical adjustment,significantly reducing operational complexity.Due to the advantages of broadband focusing,simple control mode,real-time monitoring,and so on,the device may have extensive applications in the fields of acoustic imaging,nondestructive testing,ultrasound medical treatment,etc.
基金Project supported by the Natural Science Foundation of Sichuan Province(2024NSFSC0219)。
文摘In this work,the rare-earth doped ternary lead zirconate titanate ceramics with chemical formula of[0.3 Pb(Zn_(1/3)Nb_(2/3))O_(3)-0.7Pb(Zr_(0.52)Ti_(0.48))O_(3)]+x wt%CeO_(2)(x=0-0.5,abbreviated as 0.3PZN-0.7PZT-xCe)were synthesized by a conventional solid-state reaction route,specific attentions was focused on the effects of CeO_(2)dopants on the structures and electrical properties of the 0.3PZN-0.7PZT ceramics,revealing the role conve rsion of CeO_(2)dopants with its doping amount(x).When less CeO_(2)(x≤0.2)is introduced into 0.3PZN-0.7PZT,the prepared ceramics are identified as the coexistence of rhombohedral and tetragonal phases,also involved with an increased grain size and a reduced atomic ratio of Pb/(Zr+Ti+Zn+Nb).The increased remanent polarization(Pr)and deceased coercive filed(Ec),as well as improved dielectric permittivity(er)and piezoelectric coefficient(d_(33))de monstrate the donor substitution of Ce^(3+)for Pb^(2+)at the A-site of perovskite lattice.Conversely,the introduction of excessive CeO_(2)(x>0.2)causes a reversal evolution in the electrical properties of ceramics,suggesting that some of the introduced cerium element tends to become Ce4+,which equivalently substitutes for Zr^(4+)at the B-site.Additionally,the diffused phase transition(DPT)behaviors of the 0.3PZN-0.7PZT-xCe ceramics were investigated by the modified Curie-Weiss Law.The sample with x=0.2 shows reduced DPT character and optimized electrical properties,including TC=297℃,εr=1400,d_(33)=480 pC/N,tanδ=1.6%,kp=65%,d_(33)·g_(33)=16.32×10^(-12)m^(2)/N,Pr=38.3μC/cm^(2)and Ec=1.02 kV/mm.These enhanced electrical properties not only are contributed by the donor substitution effect of Ce^(3+),but also benefit from the optimized morphotropic phase boundary that is close to the tetragonal-rich side.
基金supported by the National Natural Science Foundation of China(Grant Nos.51202273,11204304,and 11304334)the Science and Technology Commission of Shanghai Municipality,China(Grant No.14DZ2261000)
文摘The phase transitions, dielectric properties, and polarization versus electric field （P-E） hysteresis loops of Pbo.97Lao.02（Zr0.42Sn0.58-xTix）O3 （0.13≤ x ≤0.18） （PLZST） bulk ceramics were systematically investigated. This study exhibited a sequence of phase transitions by analyzing the change of the P-E hysteresis loops with increasing temperature. The anfiferroelectric （AFE） to ferroelectric （FE） phase boundary of PLZST with the Zr content of 0.42 was found to locate at the Ti content between 0.14 and 0.15. This work is aimed to improve the ternary phase diagram of lanthanum-doped PZST with the Zr content of 0.42 and will be a good reference for seeking high energy storage density in the PLZST system with low-Zr content.
文摘The brazing of Al 2O 3 to Nb was achieved by the method of transient liquid phase (TLP) bonding. Ti foil and Ni 5V alloy foil were used as interlayers for the bonding. The base materials were brazed at 1 4231 573 K for 1120 min. The results show that the shear strength of the joint first increases and then decreases with increasing holding time and brazing temperature. The joint interface microstructure and elements distribution were investigated. It can be concluded that a composite structure, in which the base metals are solid solution Nb(V) and Nb(Ti) reinforced by Ni 2Ti, is formed when the brazing temperature is 1 473 K and holding time 15 min, and a satisfactory joint strength can be achieved. The interaction of Ti foil and Ni 5V foil leads to the formation of liquid eutectic phase with low melting point, at the same time the combination of Ti come from the interlayer with O atoms from Al 2O 3 results in the bonding of Al 2O 3 and Nb.
文摘Dielectric materials are essential in modern electronics,serving as the backbone of numerous components across a wide array of electronic devices[1,2].As technology advances,the demand for materials with high permittivity,low dielectric loss,and thermal stability continues to rise.Traditional strategies to enhance permittivity often involve mechanisms such as phase transitions in ferroelectrics or interfacial polarization in boundary layer capacitor(IBLC)systems.However,each comes with trade-offs.
