(NbZrHfTi)C high-entropy ceramics,as an emerging class of ultra-high-temperature materials,have garnered significant interest due to their unique multi-principal-element crystal structure and exceptional hightemperatu...(NbZrHfTi)C high-entropy ceramics,as an emerging class of ultra-high-temperature materials,have garnered significant interest due to their unique multi-principal-element crystal structure and exceptional hightemperature properties.This study systematically investigates the mechanical properties of(NbZrHfTi)C high-entropy ceramics by employing first-principles density functional theory,combined with the Debye-Grüneisen model,to explore the variations in their thermophysical properties with temperature(0–2000 K)and pressure(0–30 GPa).Thermodynamically,the calculated mixing enthalpy and Gibbs free energy confirm the feasibility of forming a stable single-phase solid solution in(NbZrHfTi)C.The calculated results of the elastic stiffness constant indicate that the material meets the mechanical stability criteria of the cubic crystal system,further confirming the structural stability.Through evaluation of key mechanical parameters—bulk modulus,shear modulus,Young’s modulus,and Poisson’s ratio—we provide comprehensive insight into the macro-mechanical behaviour of the material and its correlation with the underlying microstructure.Notably,compared to traditional binary carbides and their average properties,(NbZrHfTi)C exhibits higher Vickers hardness(Approximately 28.5 GPa)and fracture toughness(Approximately 3.4 MPa⋅m^(1/2)),which can be primarily attributed to the lattice distortion and solid-solution strengthening mechanism.The study also utilizes the quasi-harmonic approximation method to predict the material’s thermophysical properties,including Debye temperature(initial value around 563 K),thermal expansion coefficient(approximately 8.9×10^(−6) K−1 at 2000 K),and other key parameters such as heat capacity at constant volume.The results show that within the studied pressure and temperature ranges,(NbZrHfTi)C consistently maintains a stable phase structure and good thermomechanical properties.The thermal expansion coefficient increasing with temperature,while heat capacity approaches the Dulong-Petit limit at elevated temperatures.These findings underscore the potential of(NbZrHfTi)C applications in ultra-high temperature thermal protection systems,cutting tool coatings,and nuclear structural materials.展开更多
The recycling of waste activated carbon is of great significance in environmental protection.Porous mullite ceramics were prepared by impregnating the mullite precursor with activated carbon,adding a pore-forming agen...The recycling of waste activated carbon is of great significance in environmental protection.Porous mullite ceramics were prepared by impregnating the mullite precursor with activated carbon,adding a pore-forming agent,and adopting aluminum sulfate octahydrate,ammonia and silica micropowder as raw materials,waste activated carbon after heat treatment as the pore-forming agent,and sodium polyacrylate(PAAS)as the dispersant.The effects of the activated carbon additions(1.5%,3.0%,5.2%,and 7.8%,by mass)and PAAS additions(1%,2%,and 3%,extra adding,by mass)on the physical properties,phase composition and microstructure of the porous ceramics were studied.The results show that:(1)as a pore-forming agent,activated carbon promotes the formation of pores inside the samples,while the apparent porosity of the samples increases significantly with the increasing activated carbon addition;when the activated carbon addition is 7.8%,the apparent porosity of the sample is 65.7%,the cold compressive strength is 4.62 MPa,the peak pore size is around 3.5μm,and the pore size distribution is uniform;(2)appropriate PAAS helps to improve the dispersion of activated carbon in the samples and the comprehensive performance of the porous mullite ceramics;when the PAAS addition is 2%,the apparent porosity of the sample is 71.8%,the cold compressive strength is 5.53 MPa,the peak pore size is around 3μm,and the pore size distribution is optimized;however,excessive PAAS increases the liquid phase in the system,resulting in over sintering of mullite and a decrease in the porosity.展开更多
Gradient refractive index(GRIN)metalenses are increasingly valued in high-frequency communication due to their exceptional radiation performance.Ceramics with high dielectric constants and low dielectric losses are id...Gradient refractive index(GRIN)metalenses are increasingly valued in high-frequency communication due to their exceptional radiation performance.Ceramics with high dielectric constants and low dielectric losses are ideal candidates for GRIN metalenses.Digital light processing(DLP)3D printing provides a feasible and efficient approach for manufacturing ceramic GRIN metalenses.However,the scattering of ultraviolet(UV)light by ceramic particles in the slurry reduces the printing accuracy of DLP technology,making it difficult to achieve the intricate structural features required for GRIN metalenses in high-frequency communication.In this work,we propose an approach to improve printing accuracy by optimizing the ceramic slurry composition and implementing a dimensional compensation design strategy.Utilizing geometric optics and the S-parameter inversion method,we design a GRIN metalens consisting of two distinct types of subwavelength unit cells(Y-shaped and circular hole geometries)with a minimum feature size of 160μm.Through a refined slurry formulation and precise design parameter compensation,high-fidelity ceramic GRIN metalenses are successfully fabricated.The fabricated metalens exhibits a maximum gain enhancement of 18.4 dBi and a deflection angle of±30°over a bandwidth of 37.84% in the W-band(75-110 GHz).The highly directional far-field beam radiation and efficient beam steering capabilities highlight the potential of ceramic GRIN metalenses for applications in satellite communications,radar systems,and other high-frequency technologies.展开更多
The cold sintering process(CSP)is a green and innovative method of material densification at low temperatures(<350°C).The traditional CSP entails the addition of liquid phases as a solvent to achieve material ...The cold sintering process(CSP)is a green and innovative method of material densification at low temperatures(<350°C).The traditional CSP entails the addition of liquid phases as a solvent to achieve material densification through the dissolution-precipitation mechanism.However,it is difficult to realize for materials with low solubility.To address this challenge,a universal cold sintering method without the addition of liquid phases has been proposed in this work.The addition of a special polyester-polymer assisted the densification of insoluble ceramics,and hydroxyapatite(HA)and Al_(2)O_(3)were successfully sintered below 100°C,achieving 95-100%densities in a short time(5-20 min).This achievement can be attributed to the low glass transition temperature and the abundance of active sites(C=O)of the polyester-polymer.The denser ceramics exhibited enhanced mechanical properties,with the compression strength of polymer-assisted CSP HA increasing by 147.3%compared to the nanoparticles.Additionally,serving as an advanced bone substitute material,HA underwent quantitative analysis using the CCK-8 method and assessed the impact of polymer presence on cell proliferation and cytotoxicity.Meanwhile,a tight bonding between the polymer and ceramic materials was achieved during CSP,providing a generalized method for designing multifunctional ceramic-polymer.展开更多
A series of high-entropy ceramics with the nominal composition(Mg_(0.5)Zn_(0.5))_(0.4+x)Li_(0.4)(Ca_(0.5)Sr_(0.5))_(0.4−x)TiO_(3)(0≤x≤0.4)has been successfully synthesized using the conventional solid-phase method.T...A series of high-entropy ceramics with the nominal composition(Mg_(0.5)Zn_(0.5))_(0.4+x)Li_(0.4)(Ca_(0.5)Sr_(0.5))_(0.4−x)TiO_(3)(0≤x≤0.4)has been successfully synthesized using the conventional solid-phase method.The(Mg_(0.5)Zn_(0.5))_(0.4+x)Li_(0.4)(Ca_(0.5)Sr_(0.5))_(0.4−x)TiO_(3)ceramics are confirmed to be composed of the main phase(Zn,Mg,Li)TiO_(3)and the secondary phase Ca_(0.5)Sr_(0.5)TiO_(3)by X-ray diffractometer,Rietveld refinement,and X-ray spectroscopy analysis.The quality factor(Q×f)of the samples is inversely proportional to the content of the Ca_(0.5)Sr_(0.5)TiO_(3)phase,and it is influenced by the density.The secondary phase and molecular polarizability(α_(T))have a significant impact on the dielectric constant(ε_(r))of the samples.Moreover,the temperature coefficient of resonant frequency(τ_(f))of the samples is determined by the distortion of[TiO_(6)]octahedra and the secondary phase.The results indicate tha(Mg_(0.5)Zn_(0.5))_(0.4+x)Li_(0.4)(Ca_(0.5)Sr_(0.5))_(0.4−x)TiO_(3)ceramics achieve ideal microwave dielectric properties(ε_(r)=17.6,Q×f=40900 GHz,τ_(f)=-8.6 ppm/℃)when x=0.35.(Mg_(0.5)Zn_(0.5))_(0.4+x)Li_(0.4)(Ca_(0.5)Sr_(0.5))_(0.4−x)TiO_(3)ceramics possess the potential for application in wireless communication,and a new approach has been provided to enhance the perform-ance of microwave dielectric ceramics.展开更多
Over the past several decades,much research effort has been dedicated to the study of optical windows,with two primary themes emerging as key focuses.The first of these centers on investigating the optical properties ...Over the past several decades,much research effort has been dedicated to the study of optical windows,with two primary themes emerging as key focuses.The first of these centers on investigating the optical properties of typical transparent single crystals under shock or ramp compression,which helps in the selection of appropriate optical windows for high-pressure experiments.The second involves the exploration of novel optical windows,particularly transparent polycrystalline ceramics,which not only match the shock impedance of the samples,but also preserve transparency under dynamic compression.In this study,we first integrate existing research on the evolution of optical properties in transparent single crystals and polycrystalline ceramics subjected to shock or ramp loading,proposing a mechanism that links mesoscopic damage to macroscopic optical transparency.Subsequently,through a systematic integration of experiments and computational analyses on polycrystalline transparent ceramics,we demonstrate that shock transparency can be enhanced by optimizing grain size and that shock impedance can be designed via compositional tuning.Notably,our results reveal that nano-grained MgAl_(2)O_(4) ceramics exhibit outstanding optical transparency under high shock pressures,highlighting a promising strategy for designing optical windows that retain transparency under extreme dynamic loading conditions.展开更多
Combined pulsed laser(CPL),introduced in 1975 for target damage,integrates different lasers to achieve high peak power and pulse energy.However,despite decades of research,CPL remains unused for long-range target dama...Combined pulsed laser(CPL),introduced in 1975 for target damage,integrates different lasers to achieve high peak power and pulse energy.However,despite decades of research,CPL remains unused for long-range target damage due to the challenge of maintaining high peak power density over long distances.We note that a potential solution lies in leveraging the air filament generated by femtosecond laser,which can transmit peak power densities higher than 1014 W/cm^(2)under the power clamping effect.To address this,a concept of a femtosecond laser induced air filament-CW CPL for surface damage of ceramics was introduced.We found no surface changes in ceramic targets when irradiated with a CW laser alone.By way of contrast,the target can be penetrated in a very short time(20 ms)with the assistance of the femtosecond laser induced air filament.In this context,we employ high-speed shadow imaging,cross-timescale simulation models and macro-microscopic characterization,to elucidate the CPL damage mechanism.The optimal CPL,combining a 1 mJ femtosecond laser and a 500 W CW laser,yields a damage rate of 1.51×10^(7)μm^(3)/J,representing an improvement of approximately 175%compared to single femtosecond laser ablation and around 59%enhancement compared to coating-assisted CW laser ablation.Furthermore,the efficacy of the proposed femtosecond-CW CPL method is demonstrated in causing penetration damage of ceramic/metal composite material or direct damage of sapphire,showcasing its versatility in damaging applications.Consequently,the femtosecond-CW CPL ablation method presented in this paper holds great promise as a new type of damage method for transparent hard and brittle materials.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
Thermal and mechanical properties of yttrium tantalate(YTaO_(4)),a top coat ceramic of thermal barrier coatings(TBCs)for aeroengines,are enhanced by synthesizing Y_(1-x)Ta_(1-x)M_(2x)O_(4)(M=Ti,Zr,Hf;x=0.06,0.12,0.18,...Thermal and mechanical properties of yttrium tantalate(YTaO_(4)),a top coat ceramic of thermal barrier coatings(TBCs)for aeroengines,are enhanced by synthesizing Y_(1-x)Ta_(1-x)M_(2x)O_(4)(M=Ti,Zr,Hf;x=0.06,0.12,0.18,0.24)medium-entropy ceramics(MECs)using a two-step sintering method.In addition,the thermal conductivity,thermal expansion coefficients(TECs),and fracture toughness of MECs were investigated.An X-ray diffraction study revealed that the Y_(1-x)Ta_(1-x)M_(2x)O_(4) MECs were monoclinic,and the Ti,Zr,and Hf doping elements replaced Y and Ta.The variations in atomic weights and ionic radii led to disturbed atomic arrangements and severe lattice distortions,resulting in improving the phonon scattering and reduced thermal conductivity,with Y_(1-x)Ta_(1-x)M_(2x)O_(4) MECs(x=0.24)exhibiting the lowest thermal conductivity of 1.23 W·m^(-1)·K^(-1)at 900℃.The introduction of MO_(2) increased the configurational entropy and weakened the ionic bonding energy,obtaining high TECs(10.4×10^(-6)K^(-1)at 1400℃).The reduction in the monoclinic angle β lowered the ferroelastic domain inversion energy barrier.Moreover,microcracks and crack extension toughening endowed Y_(1-x)Ta_(1-x)M_(2x)O_(4) MECs(x=0.24)with the highest fracture toughness of(4.1±0.5)MPa·m~(1/2).The simultaneous improvement of the thermal and mechanical properties of the MO_(2)(M=Ti,Zr,Hf)co-doped YTaO_(4) MECs can be extended to other materials.展开更多
Hafnium carbonitride(HfC_(x)N_(1-x))ceramics have drawn considerable interest due to their exceptional me-chanical and thermophysical properties.Herein,we report a novel single-source precursor with Hf-N bonds as the ...Hafnium carbonitride(HfC_(x)N_(1-x))ceramics have drawn considerable interest due to their exceptional me-chanical and thermophysical properties.Herein,we report a novel single-source precursor with Hf-N bonds as the main chain and fabricate HfC_(x)N_(1-x)ceramics after pyrolysis of the precursor.The synthesis,ceramic conversion,and microstructural evolution of the single-source precursor as well as the derived HfC_(x)N_(1-x)ceramics treated under various atmospheres were investigated.The results indicate that in an argon atmosphere,the nitrogen content within HfC_(x)N_(1-x)decreases with rising temperature.While under a nitrogen atmosphere,the high concentration of N_(2)facilitates the rapid conversion of HfO2 to Hf7O8N4,which subsequently promotes the transformation of the HfC_(x)N_(1-x)solid solution ceramics.During this process,there is also an inhibitory effect of N_(2)on the tendency of HfN into HfC.Moreover,the desired chemical composition of HfC_(x)N_(1-x)can be regulated by adjusting the N_(2)concentration in the heat treat-ment atmosphere.The present work proposes a novel strategy for the single-source precursor-derived carbonitride ceramics and provides a deep understanding of the preparation and property modulation of HfC_(x)N_(1-x)ceramics.展开更多
High-entropy ceramics have exhibited promising application prospects in aerospace,electronic devices,and extreme environment protection.Current powder sintering routes for preparing high-entropy ceramics are hindered ...High-entropy ceramics have exhibited promising application prospects in aerospace,electronic devices,and extreme environment protection.Current powder sintering routes for preparing high-entropy ceramics are hindered by stringent powder requirements,reliance on long-term high-temperature and high-pressure synthesis,as well as compositional inhomogeneity and coarse grains.In this work,the low-temperature glass crystallization method was innovatively introduced into the preparation of high-entropy ceramics.展开更多
The types of dopants lead to distinctive microstructural evolution behavior and physical properties in materials.In this study,the effect of stoichiometric and non-stoichiometric Mn modification,namely Pb(Mn_(1/3) Nb_...The types of dopants lead to distinctive microstructural evolution behavior and physical properties in materials.In this study,the effect of stoichiometric and non-stoichiometric Mn modification,namely Pb(Mn_(1/3) Nb_(2/3))O_(3)(PMnN)and MnO_(2),on the microstructure and properties of Pb(Yb_(1/2) Nb_(1/2))O_(3)-PbZrO_(3)-PbTiO_(3)(PYN-PZT)piezoelectric ceramics are systematically investigated.It was found that stoichiometric PMnN modification inhibits the grain growth while non-stoichiometric MnO_(2) modification promotes it,and thus the former yields stronger high-power characteristics(higher internal bias field Ei and larger mechanical quality factor Q_(m))than the latter.Specifically,with an equivalent amount of Mn modifica-tion(2 mol%),PMnN and MnO_(2) modification PYN-PZT ceramics exhibit significantly different values for average grain size(1.21μm vs.14.12μm),Ei(8.5 kV/cm vs.5 kV/cm),and Qm(2376 vs.1134).To further evaluate high-power performance,the vibration velocity v of these two modified PYN-PZT under high driving conditions was measured.Under an AC electric field of 3.5 V/mm,the PYN-PZT+6PMnN ceram-ics exhibit a v of up to 0.95 m s^(−1),larger than both MnO2-doped PYN-PZT(0.72 m s^(−1))and unmodified PYN-PZT ceramics(0.1 m s^(−1)),and far outperformance than both PZT-4 and PZT-8 ceramics.Furthermore,to elucidate the origin of the exceptional high-power performance of PMnN-modified PYN-PZT,we per-formed phase-field simulations revealing a pinning effect of the grain boundary on domain wall motion.Consequently,the small grain size(high grain boundary density)in PMnN-modified PYN-PZT exhibits a strong pinning effect,resulting in a large Q_(m) and outstanding high-power performance.展开更多
Al_(2)O_(3)-based eutectic ceramics are considered as promising candidates for ultra-high-temperature structural materials due to their exceptional thermal stability and mechanical properties.Nonetheless,several chall...Al_(2)O_(3)-based eutectic ceramics are considered as promising candidates for ultra-high-temperature structural materials due to their exceptional thermal stability and mechanical properties.Nonetheless,several challenges must be overcome before they can be widely used.This paper reviews in detail the tailoring of microstructure from the aspect of process parameters,the updated knowledge gained in microstructure(crystallographic orientation,high-resolution interfacial structures)and the latest means of optimizing eutectic microstructure(seed-induced method,introducing low-energy grain boundaries and high-entropy phase).Additionally,the paper explores future techniques for the fabrication of bulk ceramic materials and effective toughening approaches.This review highlights the achievements made especially in the last 15 years,current limitations in Al_(2)O_(3)-based eutectic ceramics,and offers comprehensive insights and strategic guidance for further mechanical breakthroughs.展开更多
With rapid advancements in physics and particle medicine,the domestic accelerator industry has grown rapidly.During the 12th Five-Year Plan period,the Institute of Modern Physics of the Chinese Academy of Sciences too...With rapid advancements in physics and particle medicine,the domestic accelerator industry has grown rapidly.During the 12th Five-Year Plan period,the Institute of Modern Physics of the Chinese Academy of Sciences took on a plurality of accelerator projects.Nevertheless,the stability of the coupler,a crucial system within the cavities of accelerators,has encountered certain difficulties.The alumina ceramics,which constitute the core component of the coupler,are increasingly prone to breakage and solder joint failures due to their inferior environmental adaptability,inadequate mechanical properties,and high gas emissions.Conversely,with the advancements in medical technology and materials science,zirconia ceramics have emerged as a prospective remedy for these problems.This type of ceramic is highly esteemed for its outstanding environmental adaptability,remarkable mechanical properties,and excellent high-temperature resistance,exhibiting extraordinary value in dental applications.This study investigates the use of zirconia ceramics in a 162.5 MHz 3-1/8"standard ceramic window,combining experimental data with finite element RF simulations and multi-physics analysis.A new coupler featuring a zirconia ceramic window was tested on a Quarter-Wave Resonator,demonstrating excellent alignment between electromagnetic simulations and measurement results.This reveals the substantial application potential and practical worth of the zirconia ceramic material in the context of accelerators.展开更多
The structural phase transitions and ferroelectric dynamics of lead-free AgNbO_(3)have attracted consid-erable attention owing to their potential in energy-storage device applications.Here,we examine the impact of Li+...The structural phase transitions and ferroelectric dynamics of lead-free AgNbO_(3)have attracted consid-erable attention owing to their potential in energy-storage device applications.Here,we examine the impact of Li+doping on the phase transitions and polarization behavior of(Ag_(1-x)Li_(x))NbO_(3)(x=0-7%)ceramics through comprehensive dielectric and ferroelectric analyses.Rietveld refinement reveals a Li+-induced phase transition from Pbcm to R3c,with x=5%and x=6%compositions near the morphotropic phase boundary(MPB).Dielectric anomalies identify key characteristic temperatures,supporting the con-struction of a low-field phase diagram.High-field studies uncover a direct relationship between phase structure and polarization behavior,culminating in a high-field phase diagram.Near-MPB compositions exhibit distinct structural states,elucidating the mechanisms of reversible and irreversible phase transi-tions.This work provides a comprehensive explanation of the evolution of hysteresis loop profiles,capturing their progression from double hysteresis loops to square loops and their subsequent reversion to double loops under varying electric field and temperature conditions.These temperature-composition(T-x)and temperature-electric field(T-E)phase diagrams provide a robust framework for understanding phase evolution,offering critical insights into optimizing AgNbO_(3)-based ceramics for advanced functional applications.展开更多
Zirconia(ZrO_(2))ceramic material has been widely applied to various fields due to its unique properties of high strength,high hardness,and excessive temperature resistance.However,the high-quality micro-hole machinin...Zirconia(ZrO_(2))ceramic material has been widely applied to various fields due to its unique properties of high strength,high hardness,and excessive temperature resistance.However,the high-quality micro-hole machining of zirconia ceramic material remains a significant challenge at present.In this study,experiments on peck drilling of 0.2 mm and 0.5 mm micro-holes in zirconia ceramics using diamond-coated drills are conducted.The characteristics of the force signal during the drilling process,the influence of drilling parameters on the drlling force and the chipping size at the hole exit,and features of the tool wear stages of the diamond coated drill are analyzed.Experimental results suggest that when machining micro-holes in zirconia ceramics,there is a positive correlation between the axial force and the size of the chipping at the exit.The axial force increases with the increase of the feed rate and the step distance,and it shows a trend of first increasing and next decreasing with the increase of the spindle speed.The wear of the drll bit has a significant impact on the quality of the hole exit.It is found that with the continuous drilling of seven holes,the axial force increases by 144.2%,and the size of edge chipping at the exit increases from about 20μm to more than 130μm.This study can provide some valuable references for improving the micro-hole processing quality of material.展开更多
High-entropy carbide ceramics(HECCs)exhibit superior properties compared to their constituent bi-nary compounds.However,high synthesis and sintering temperature are main obstacles that limit their widespread applicati...High-entropy carbide ceramics(HECCs)exhibit superior properties compared to their constituent bi-nary compounds.However,high synthesis and sintering temperature are main obstacles that limit their widespread applications.To address this issue,compositional and particle size controllable high-entropy(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb02Ta_(0.2))C_(x) powders were successfully prepared by a sugar hydrogel combined with the carbothermal reduction method.Owing to the introduction of carbon vacancy,the temperature for the formation of single-phase solid solution of the high-entropy(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C_(x) powders was decreased,and the addition of nitrogen decreased the densification temperature of the high-entropy(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C_(0.95) ceramic by 200℃.In addition,the flexural strength and fracture toughness of the high-entropy(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C_(0.95) ceramic were improved by 29%and 30%,respectively,compared with those without nitrogen doping.Atomic-resolution high angle annular dark field scanning transmission electron microscopy(HAADF-STEM)and energy dispersive spectroscopy(EDS)mapping re-veal that the segregation of N and small cation Ti as well as large lattice strains are responsible for the enhanced mechanical properties.Furthermore,with the introduction of nitrogen,the onset oxidation tem-perature(OOT)was increased,while the parabolic oxidation rate constant was decreased,revealing the beneficial effect of nitrogen doping on oxidation resistance.These results demonstrate that nitrogen dop-ing can not only improve the mechanical properties of HECCs but also enhance the oxidation resistance,which paves the way for the wide application of HECCs.展开更多
Outstanding electric performance can be achieved in the textured ceramics.Therefore,the Ba_(0.85)Ca_(0.15)Zr_(0.09)Ti_(0.91)O_(3)(BCZT)lead-free piezoceramics with high texture degree(f)in<001>direction were suc...Outstanding electric performance can be achieved in the textured ceramics.Therefore,the Ba_(0.85)Ca_(0.15)Zr_(0.09)Ti_(0.91)O_(3)(BCZT)lead-free piezoceramics with high texture degree(f)in<001>direction were successfully prepared using template grain growth method.On account of the perfect sheet BaTiO3(BT)templates,a texture degree as high as 97.9%for BCZT-3.0 wt%BT ceramics was obtained.The ceramics system exhibited excellent comprehensive electrical properties(d_(33)~575 pCN^(-1),k_(p)~0.61,T_(C)~89℃ε_(r)(20℃)~3002,tanδ~4.18%,P_(r)~10.91μC cm^(-2),E_(C)~2.20 kV cm^(-1)).The superior performance originated from the coexistence of rhombohedralorthorhombic-tetragonal phases(R-O-T),as well as high textured degree.The multiphase coexistence was attributed to the composition design.This work provides a theoretical basis for designing lead-free piezoceramics with excellent properties in the future.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
In the background of carbon neutrality,monolithic ceramic catalysts are universally used in energy conversion and chemical catalysis due to the high heat and mass transfer efficiencies,low bed pressures,and scalabilit...In the background of carbon neutrality,monolithic ceramic catalysts are universally used in energy conversion and chemical catalysis due to the high heat and mass transfer efficiencies,low bed pressures,and scalability through modular design.However,traditional manufacturing processes are limited by mold dependence,organic solvent toxicity,and insufficient molding capability for complex structures,resulting in difficulty achieving precise regulation of cross-scale pores.Additive manufacturing(AM)technology employs a digital layered molding strategy to achieve the cross-scale structural regulation of catalysts from macroscopic flow channels to mesopores and micropores.This paper summarizes recent advances in the structural design of monolithic catalysts enabled by AM technologies and highlights their emerging applications in catalytic processes.Structurally,AM-fabricated monoliths have been effectively employed in key chemical reactions such as fuel reforming,CO_(2)conversion,biofuel synthesis.Strategies such as geometrical topology optimization,multi-scale pore synergy,biomimetic structural design,and functional gradient integration have been utilized to enhance heat and mass transport,reduce pressure drops,and improve overall catalytic performance.By overcoming the limitations of traditional catalysts,AM technologies create a new paradigm for addressing the longstanding challenge of coupling mass transfer with reaction kinetics.This approach provides a feasible pathway for driving both theoretical innovation and practical implementation of high-efficiency catalytic systems.展开更多
基金supported by the National Natural Science Foundation of China(Nos.92166105 and 52005053)High-Tech Industry Science and Technology Innovation Leading Program of Hunan Province(No.2020GK2085)the Science and Technology Innovation Program of Hunan Province(No.2021RC3096).
文摘(NbZrHfTi)C high-entropy ceramics,as an emerging class of ultra-high-temperature materials,have garnered significant interest due to their unique multi-principal-element crystal structure and exceptional hightemperature properties.This study systematically investigates the mechanical properties of(NbZrHfTi)C high-entropy ceramics by employing first-principles density functional theory,combined with the Debye-Grüneisen model,to explore the variations in their thermophysical properties with temperature(0–2000 K)and pressure(0–30 GPa).Thermodynamically,the calculated mixing enthalpy and Gibbs free energy confirm the feasibility of forming a stable single-phase solid solution in(NbZrHfTi)C.The calculated results of the elastic stiffness constant indicate that the material meets the mechanical stability criteria of the cubic crystal system,further confirming the structural stability.Through evaluation of key mechanical parameters—bulk modulus,shear modulus,Young’s modulus,and Poisson’s ratio—we provide comprehensive insight into the macro-mechanical behaviour of the material and its correlation with the underlying microstructure.Notably,compared to traditional binary carbides and their average properties,(NbZrHfTi)C exhibits higher Vickers hardness(Approximately 28.5 GPa)and fracture toughness(Approximately 3.4 MPa⋅m^(1/2)),which can be primarily attributed to the lattice distortion and solid-solution strengthening mechanism.The study also utilizes the quasi-harmonic approximation method to predict the material’s thermophysical properties,including Debye temperature(initial value around 563 K),thermal expansion coefficient(approximately 8.9×10^(−6) K−1 at 2000 K),and other key parameters such as heat capacity at constant volume.The results show that within the studied pressure and temperature ranges,(NbZrHfTi)C consistently maintains a stable phase structure and good thermomechanical properties.The thermal expansion coefficient increasing with temperature,while heat capacity approaches the Dulong-Petit limit at elevated temperatures.These findings underscore the potential of(NbZrHfTi)C applications in ultra-high temperature thermal protection systems,cutting tool coatings,and nuclear structural materials.
文摘The recycling of waste activated carbon is of great significance in environmental protection.Porous mullite ceramics were prepared by impregnating the mullite precursor with activated carbon,adding a pore-forming agent,and adopting aluminum sulfate octahydrate,ammonia and silica micropowder as raw materials,waste activated carbon after heat treatment as the pore-forming agent,and sodium polyacrylate(PAAS)as the dispersant.The effects of the activated carbon additions(1.5%,3.0%,5.2%,and 7.8%,by mass)and PAAS additions(1%,2%,and 3%,extra adding,by mass)on the physical properties,phase composition and microstructure of the porous ceramics were studied.The results show that:(1)as a pore-forming agent,activated carbon promotes the formation of pores inside the samples,while the apparent porosity of the samples increases significantly with the increasing activated carbon addition;when the activated carbon addition is 7.8%,the apparent porosity of the sample is 65.7%,the cold compressive strength is 4.62 MPa,the peak pore size is around 3.5μm,and the pore size distribution is uniform;(2)appropriate PAAS helps to improve the dispersion of activated carbon in the samples and the comprehensive performance of the porous mullite ceramics;when the PAAS addition is 2%,the apparent porosity of the sample is 71.8%,the cold compressive strength is 5.53 MPa,the peak pore size is around 3μm,and the pore size distribution is optimized;however,excessive PAAS increases the liquid phase in the system,resulting in over sintering of mullite and a decrease in the porosity.
基金financial support by the National Key Research and Development Program of China(No.2023YFB4605400)the National Natural Science Foundation of China(No.12472152)the Department of Science and Technology of Guangdong Province(No.2019QN01Z438)。
文摘Gradient refractive index(GRIN)metalenses are increasingly valued in high-frequency communication due to their exceptional radiation performance.Ceramics with high dielectric constants and low dielectric losses are ideal candidates for GRIN metalenses.Digital light processing(DLP)3D printing provides a feasible and efficient approach for manufacturing ceramic GRIN metalenses.However,the scattering of ultraviolet(UV)light by ceramic particles in the slurry reduces the printing accuracy of DLP technology,making it difficult to achieve the intricate structural features required for GRIN metalenses in high-frequency communication.In this work,we propose an approach to improve printing accuracy by optimizing the ceramic slurry composition and implementing a dimensional compensation design strategy.Utilizing geometric optics and the S-parameter inversion method,we design a GRIN metalens consisting of two distinct types of subwavelength unit cells(Y-shaped and circular hole geometries)with a minimum feature size of 160μm.Through a refined slurry formulation and precise design parameter compensation,high-fidelity ceramic GRIN metalenses are successfully fabricated.The fabricated metalens exhibits a maximum gain enhancement of 18.4 dBi and a deflection angle of±30°over a bandwidth of 37.84% in the W-band(75-110 GHz).The highly directional far-field beam radiation and efficient beam steering capabilities highlight the potential of ceramic GRIN metalenses for applications in satellite communications,radar systems,and other high-frequency technologies.
基金supported by the Jilin Provincial Natural Science Foundation(No.20240101118JC)the funds of Medical+X cross innovation team granted by medical department of Jilin University(No.2022JBGS07)+1 种基金the Jilin Province Science and Technology development project(No.20210101437JC)the WU JIEPING Medical Foundation(No.320.6750.2023-3-20 to TGM)。
文摘The cold sintering process(CSP)is a green and innovative method of material densification at low temperatures(<350°C).The traditional CSP entails the addition of liquid phases as a solvent to achieve material densification through the dissolution-precipitation mechanism.However,it is difficult to realize for materials with low solubility.To address this challenge,a universal cold sintering method without the addition of liquid phases has been proposed in this work.The addition of a special polyester-polymer assisted the densification of insoluble ceramics,and hydroxyapatite(HA)and Al_(2)O_(3)were successfully sintered below 100°C,achieving 95-100%densities in a short time(5-20 min).This achievement can be attributed to the low glass transition temperature and the abundance of active sites(C=O)of the polyester-polymer.The denser ceramics exhibited enhanced mechanical properties,with the compression strength of polymer-assisted CSP HA increasing by 147.3%compared to the nanoparticles.Additionally,serving as an advanced bone substitute material,HA underwent quantitative analysis using the CCK-8 method and assessed the impact of polymer presence on cell proliferation and cytotoxicity.Meanwhile,a tight bonding between the polymer and ceramic materials was achieved during CSP,providing a generalized method for designing multifunctional ceramic-polymer.
基金supported by the Sichuan Science and Technology Program,China(No.2023YFQ0082)the Guangdong Provincial Key Laboratory of Electronic Functional Materials and Device,China(No.EFMD2022005Z)the State Key Laboratory of Advanced Technologies for Comprehensive Utilization of Platinum Metals,China(No.SKL-SPM-202021).
文摘A series of high-entropy ceramics with the nominal composition(Mg_(0.5)Zn_(0.5))_(0.4+x)Li_(0.4)(Ca_(0.5)Sr_(0.5))_(0.4−x)TiO_(3)(0≤x≤0.4)has been successfully synthesized using the conventional solid-phase method.The(Mg_(0.5)Zn_(0.5))_(0.4+x)Li_(0.4)(Ca_(0.5)Sr_(0.5))_(0.4−x)TiO_(3)ceramics are confirmed to be composed of the main phase(Zn,Mg,Li)TiO_(3)and the secondary phase Ca_(0.5)Sr_(0.5)TiO_(3)by X-ray diffractometer,Rietveld refinement,and X-ray spectroscopy analysis.The quality factor(Q×f)of the samples is inversely proportional to the content of the Ca_(0.5)Sr_(0.5)TiO_(3)phase,and it is influenced by the density.The secondary phase and molecular polarizability(α_(T))have a significant impact on the dielectric constant(ε_(r))of the samples.Moreover,the temperature coefficient of resonant frequency(τ_(f))of the samples is determined by the distortion of[TiO_(6)]octahedra and the secondary phase.The results indicate tha(Mg_(0.5)Zn_(0.5))_(0.4+x)Li_(0.4)(Ca_(0.5)Sr_(0.5))_(0.4−x)TiO_(3)ceramics achieve ideal microwave dielectric properties(ε_(r)=17.6,Q×f=40900 GHz,τ_(f)=-8.6 ppm/℃)when x=0.35.(Mg_(0.5)Zn_(0.5))_(0.4+x)Li_(0.4)(Ca_(0.5)Sr_(0.5))_(0.4−x)TiO_(3)ceramics possess the potential for application in wireless communication,and a new approach has been provided to enhance the perform-ance of microwave dielectric ceramics.
基金financially supported by the National Natural Science Foundation of China(Grant No.11872344)the Innovatory Development Foundation of the China Academy of Engineering Physics(Grant No.CX20210026).
文摘Over the past several decades,much research effort has been dedicated to the study of optical windows,with two primary themes emerging as key focuses.The first of these centers on investigating the optical properties of typical transparent single crystals under shock or ramp compression,which helps in the selection of appropriate optical windows for high-pressure experiments.The second involves the exploration of novel optical windows,particularly transparent polycrystalline ceramics,which not only match the shock impedance of the samples,but also preserve transparency under dynamic compression.In this study,we first integrate existing research on the evolution of optical properties in transparent single crystals and polycrystalline ceramics subjected to shock or ramp loading,proposing a mechanism that links mesoscopic damage to macroscopic optical transparency.Subsequently,through a systematic integration of experiments and computational analyses on polycrystalline transparent ceramics,we demonstrate that shock transparency can be enhanced by optimizing grain size and that shock impedance can be designed via compositional tuning.Notably,our results reveal that nano-grained MgAl_(2)O_(4) ceramics exhibit outstanding optical transparency under high shock pressures,highlighting a promising strategy for designing optical windows that retain transparency under extreme dynamic loading conditions.
基金supports from National Natural Science Foundation of China(Grant No.52105498)The science and technology innovation Program of Hunan Province(Grant No.2021RC3074)+2 种基金Advanced Laser Technology Laboratory of Anhui Province(AHL2022KF04)National Key R&D Program of China(Grant No.2023YFB14605500)Changsha Natural Science Foundation(kq2402089).
文摘Combined pulsed laser(CPL),introduced in 1975 for target damage,integrates different lasers to achieve high peak power and pulse energy.However,despite decades of research,CPL remains unused for long-range target damage due to the challenge of maintaining high peak power density over long distances.We note that a potential solution lies in leveraging the air filament generated by femtosecond laser,which can transmit peak power densities higher than 1014 W/cm^(2)under the power clamping effect.To address this,a concept of a femtosecond laser induced air filament-CW CPL for surface damage of ceramics was introduced.We found no surface changes in ceramic targets when irradiated with a CW laser alone.By way of contrast,the target can be penetrated in a very short time(20 ms)with the assistance of the femtosecond laser induced air filament.In this context,we employ high-speed shadow imaging,cross-timescale simulation models and macro-microscopic characterization,to elucidate the CPL damage mechanism.The optimal CPL,combining a 1 mJ femtosecond laser and a 500 W CW laser,yields a damage rate of 1.51×10^(7)μm^(3)/J,representing an improvement of approximately 175%compared to single femtosecond laser ablation and around 59%enhancement compared to coating-assisted CW laser ablation.Furthermore,the efficacy of the proposed femtosecond-CW CPL method is demonstrated in causing penetration damage of ceramic/metal composite material or direct damage of sapphire,showcasing its versatility in damaging applications.Consequently,the femtosecond-CW CPL ablation method presented in this paper holds great promise as a new type of damage method for transparent hard and brittle materials.
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.
文摘Thermal and mechanical properties of yttrium tantalate(YTaO_(4)),a top coat ceramic of thermal barrier coatings(TBCs)for aeroengines,are enhanced by synthesizing Y_(1-x)Ta_(1-x)M_(2x)O_(4)(M=Ti,Zr,Hf;x=0.06,0.12,0.18,0.24)medium-entropy ceramics(MECs)using a two-step sintering method.In addition,the thermal conductivity,thermal expansion coefficients(TECs),and fracture toughness of MECs were investigated.An X-ray diffraction study revealed that the Y_(1-x)Ta_(1-x)M_(2x)O_(4) MECs were monoclinic,and the Ti,Zr,and Hf doping elements replaced Y and Ta.The variations in atomic weights and ionic radii led to disturbed atomic arrangements and severe lattice distortions,resulting in improving the phonon scattering and reduced thermal conductivity,with Y_(1-x)Ta_(1-x)M_(2x)O_(4) MECs(x=0.24)exhibiting the lowest thermal conductivity of 1.23 W·m^(-1)·K^(-1)at 900℃.The introduction of MO_(2) increased the configurational entropy and weakened the ionic bonding energy,obtaining high TECs(10.4×10^(-6)K^(-1)at 1400℃).The reduction in the monoclinic angle β lowered the ferroelastic domain inversion energy barrier.Moreover,microcracks and crack extension toughening endowed Y_(1-x)Ta_(1-x)M_(2x)O_(4) MECs(x=0.24)with the highest fracture toughness of(4.1±0.5)MPa·m~(1/2).The simultaneous improvement of the thermal and mechanical properties of the MO_(2)(M=Ti,Zr,Hf)co-doped YTaO_(4) MECs can be extended to other materials.
基金supported by the National Key R&D Program of China(Grant No.2021YFA0715803)the National Natural Science Foundation of China(Grant Nos.52293373 and 52130205)+3 种基金the Special Funds of the National Natural Science Foun-dation of China(Grant No.52342207)the National Science and Technology Major Project(Grant No.J2022-VI-0011-0042)the Joint Fund of Henan Province Science and Technology R&D Program(Grant No.225200810002)the Research Foundation of the Science and Technology on Thermostructural Composite Materials Laboratory(Grant No.JCKYS2024607001-1).
文摘Hafnium carbonitride(HfC_(x)N_(1-x))ceramics have drawn considerable interest due to their exceptional me-chanical and thermophysical properties.Herein,we report a novel single-source precursor with Hf-N bonds as the main chain and fabricate HfC_(x)N_(1-x)ceramics after pyrolysis of the precursor.The synthesis,ceramic conversion,and microstructural evolution of the single-source precursor as well as the derived HfC_(x)N_(1-x)ceramics treated under various atmospheres were investigated.The results indicate that in an argon atmosphere,the nitrogen content within HfC_(x)N_(1-x)decreases with rising temperature.While under a nitrogen atmosphere,the high concentration of N_(2)facilitates the rapid conversion of HfO2 to Hf7O8N4,which subsequently promotes the transformation of the HfC_(x)N_(1-x)solid solution ceramics.During this process,there is also an inhibitory effect of N_(2)on the tendency of HfN into HfC.Moreover,the desired chemical composition of HfC_(x)N_(1-x)can be regulated by adjusting the N_(2)concentration in the heat treat-ment atmosphere.The present work proposes a novel strategy for the single-source precursor-derived carbonitride ceramics and provides a deep understanding of the preparation and property modulation of HfC_(x)N_(1-x)ceramics.
基金financially supported by the National Natural Science Foundation of China(NSFC No.52472062 and 51972304)the project of the Space Application System of China Manned Space Program+1 种基金the Beijing Nova Program,Chinese Academy of Sciences President’s International Fel owship Initiative for 2021(No.2021VEA0012)the Fundamental Research Funds for the Central Universities。
文摘High-entropy ceramics have exhibited promising application prospects in aerospace,electronic devices,and extreme environment protection.Current powder sintering routes for preparing high-entropy ceramics are hindered by stringent powder requirements,reliance on long-term high-temperature and high-pressure synthesis,as well as compositional inhomogeneity and coarse grains.In this work,the low-temperature glass crystallization method was innovatively introduced into the preparation of high-entropy ceramics.
基金supported by the National Key Research and Development Program of China(No.2023YFF0720700)the National Natural Science Foundation of China(Nos.52032010 and 52272120)the Central Government Funds of Guiding Local Scientific and Technological Development for Sichuan Province(No.2022ZYD0018).
文摘The types of dopants lead to distinctive microstructural evolution behavior and physical properties in materials.In this study,the effect of stoichiometric and non-stoichiometric Mn modification,namely Pb(Mn_(1/3) Nb_(2/3))O_(3)(PMnN)and MnO_(2),on the microstructure and properties of Pb(Yb_(1/2) Nb_(1/2))O_(3)-PbZrO_(3)-PbTiO_(3)(PYN-PZT)piezoelectric ceramics are systematically investigated.It was found that stoichiometric PMnN modification inhibits the grain growth while non-stoichiometric MnO_(2) modification promotes it,and thus the former yields stronger high-power characteristics(higher internal bias field Ei and larger mechanical quality factor Q_(m))than the latter.Specifically,with an equivalent amount of Mn modifica-tion(2 mol%),PMnN and MnO_(2) modification PYN-PZT ceramics exhibit significantly different values for average grain size(1.21μm vs.14.12μm),Ei(8.5 kV/cm vs.5 kV/cm),and Qm(2376 vs.1134).To further evaluate high-power performance,the vibration velocity v of these two modified PYN-PZT under high driving conditions was measured.Under an AC electric field of 3.5 V/mm,the PYN-PZT+6PMnN ceram-ics exhibit a v of up to 0.95 m s^(−1),larger than both MnO2-doped PYN-PZT(0.72 m s^(−1))and unmodified PYN-PZT ceramics(0.1 m s^(−1)),and far outperformance than both PZT-4 and PZT-8 ceramics.Furthermore,to elucidate the origin of the exceptional high-power performance of PMnN-modified PYN-PZT,we per-formed phase-field simulations revealing a pinning effect of the grain boundary on domain wall motion.Consequently,the small grain size(high grain boundary density)in PMnN-modified PYN-PZT exhibits a strong pinning effect,resulting in a large Q_(m) and outstanding high-power performance.
基金financially supported by the National Natural Science Foundation of China(No.52171046)National Natural Science Foundation of China-key programme(No.52234010)the Fundamental Research Funds for the Central Universities and Shaanxi Provincial Key Science and Technology Innovation Team(No.2023-CX-TD-14).
文摘Al_(2)O_(3)-based eutectic ceramics are considered as promising candidates for ultra-high-temperature structural materials due to their exceptional thermal stability and mechanical properties.Nonetheless,several challenges must be overcome before they can be widely used.This paper reviews in detail the tailoring of microstructure from the aspect of process parameters,the updated knowledge gained in microstructure(crystallographic orientation,high-resolution interfacial structures)and the latest means of optimizing eutectic microstructure(seed-induced method,introducing low-energy grain boundaries and high-entropy phase).Additionally,the paper explores future techniques for the fabrication of bulk ceramic materials and effective toughening approaches.This review highlights the achievements made especially in the last 15 years,current limitations in Al_(2)O_(3)-based eutectic ceramics,and offers comprehensive insights and strategic guidance for further mechanical breakthroughs.
文摘With rapid advancements in physics and particle medicine,the domestic accelerator industry has grown rapidly.During the 12th Five-Year Plan period,the Institute of Modern Physics of the Chinese Academy of Sciences took on a plurality of accelerator projects.Nevertheless,the stability of the coupler,a crucial system within the cavities of accelerators,has encountered certain difficulties.The alumina ceramics,which constitute the core component of the coupler,are increasingly prone to breakage and solder joint failures due to their inferior environmental adaptability,inadequate mechanical properties,and high gas emissions.Conversely,with the advancements in medical technology and materials science,zirconia ceramics have emerged as a prospective remedy for these problems.This type of ceramic is highly esteemed for its outstanding environmental adaptability,remarkable mechanical properties,and excellent high-temperature resistance,exhibiting extraordinary value in dental applications.This study investigates the use of zirconia ceramics in a 162.5 MHz 3-1/8"standard ceramic window,combining experimental data with finite element RF simulations and multi-physics analysis.A new coupler featuring a zirconia ceramic window was tested on a Quarter-Wave Resonator,demonstrating excellent alignment between electromagnetic simulations and measurement results.This reveals the substantial application potential and practical worth of the zirconia ceramic material in the context of accelerators.
基金finically supported by the National Natural Science Foundation of China(Nos.52261135548,52302153,and 52402155)the China Postdoctoral Science Foundation(Nos.GZC20232075 and 2023M742767)+2 种基金The research was made possible by Russian Science Foundation(Project No 23-42-00116)The equipment of the Ural Center for Shared Use“Modern nanotech-nology”Ural Federal University(Reg.No2968)whichis supported by the Ministry of Science and Higher Education RF(Project No 075-15-2021-677)was usedThe SEM work was done at International Center for Dielectric Research(ICDR),Xi’an Jiaotong University,Xi’an,China.
文摘The structural phase transitions and ferroelectric dynamics of lead-free AgNbO_(3)have attracted consid-erable attention owing to their potential in energy-storage device applications.Here,we examine the impact of Li+doping on the phase transitions and polarization behavior of(Ag_(1-x)Li_(x))NbO_(3)(x=0-7%)ceramics through comprehensive dielectric and ferroelectric analyses.Rietveld refinement reveals a Li+-induced phase transition from Pbcm to R3c,with x=5%and x=6%compositions near the morphotropic phase boundary(MPB).Dielectric anomalies identify key characteristic temperatures,supporting the con-struction of a low-field phase diagram.High-field studies uncover a direct relationship between phase structure and polarization behavior,culminating in a high-field phase diagram.Near-MPB compositions exhibit distinct structural states,elucidating the mechanisms of reversible and irreversible phase transi-tions.This work provides a comprehensive explanation of the evolution of hysteresis loop profiles,capturing their progression from double hysteresis loops to square loops and their subsequent reversion to double loops under varying electric field and temperature conditions.These temperature-composition(T-x)and temperature-electric field(T-E)phase diagrams provide a robust framework for understanding phase evolution,offering critical insights into optimizing AgNbO_(3)-based ceramics for advanced functional applications.
基金supported by the National Natural Science Foundation of China(Nos.51805242,52475463).
文摘Zirconia(ZrO_(2))ceramic material has been widely applied to various fields due to its unique properties of high strength,high hardness,and excessive temperature resistance.However,the high-quality micro-hole machining of zirconia ceramic material remains a significant challenge at present.In this study,experiments on peck drilling of 0.2 mm and 0.5 mm micro-holes in zirconia ceramics using diamond-coated drills are conducted.The characteristics of the force signal during the drilling process,the influence of drilling parameters on the drlling force and the chipping size at the hole exit,and features of the tool wear stages of the diamond coated drill are analyzed.Experimental results suggest that when machining micro-holes in zirconia ceramics,there is a positive correlation between the axial force and the size of the chipping at the exit.The axial force increases with the increase of the feed rate and the step distance,and it shows a trend of first increasing and next decreasing with the increase of the spindle speed.The wear of the drll bit has a significant impact on the quality of the hole exit.It is found that with the continuous drilling of seven holes,the axial force increases by 144.2%,and the size of edge chipping at the exit increases from about 20μm to more than 130μm.This study can provide some valuable references for improving the micro-hole processing quality of material.
基金supported by the National Natural Science Foundation of China(Nos.52272060,51902067,51872066 and 52002001)the Key Program of National Natural Science Foundation of China(No.52032003)+6 种基金the China Postdoctoral Sci-ence Foundation(Nos.2019M651282 and 2022T150157)the Hei-longjiang Provincial Postdoctoral Science Foundation(Nos.LBH-Z19022 and LBH-TZ2207)Heilongjiang Touyan Innovation Team Program,the Shanghai Aerospace Science and Technology Innova-tion Fund(No.SAST2019-012)the Fundamental Research Funds for the Central Universities(No.FRFCU5710051022)the Science Foundation of National Key Laboratory of Science and Tech-nology on Advanced Composites in Special Environments(No.JCKYS2022603C011)the Domestic Visiting and Studying Project for Outstanding Young Key Talents in Universities of Anhui Province(No.gxgnfx2021131)Young and Middle-aged Top Talent Project of Anhui Polytechnic University.
文摘High-entropy carbide ceramics(HECCs)exhibit superior properties compared to their constituent bi-nary compounds.However,high synthesis and sintering temperature are main obstacles that limit their widespread applications.To address this issue,compositional and particle size controllable high-entropy(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb02Ta_(0.2))C_(x) powders were successfully prepared by a sugar hydrogel combined with the carbothermal reduction method.Owing to the introduction of carbon vacancy,the temperature for the formation of single-phase solid solution of the high-entropy(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C_(x) powders was decreased,and the addition of nitrogen decreased the densification temperature of the high-entropy(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C_(0.95) ceramic by 200℃.In addition,the flexural strength and fracture toughness of the high-entropy(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C_(0.95) ceramic were improved by 29%and 30%,respectively,compared with those without nitrogen doping.Atomic-resolution high angle annular dark field scanning transmission electron microscopy(HAADF-STEM)and energy dispersive spectroscopy(EDS)mapping re-veal that the segregation of N and small cation Ti as well as large lattice strains are responsible for the enhanced mechanical properties.Furthermore,with the introduction of nitrogen,the onset oxidation tem-perature(OOT)was increased,while the parabolic oxidation rate constant was decreased,revealing the beneficial effect of nitrogen doping on oxidation resistance.These results demonstrate that nitrogen dop-ing can not only improve the mechanical properties of HECCs but also enhance the oxidation resistance,which paves the way for the wide application of HECCs.
基金financially supported by the National Natural Science Foundation of China(NSFC Nos.51862003,52472122)Guizhou Provincial Basic Research Program(Natural Science)(No.QKHJC-ZK-2023-266)+1 种基金Natural Science Project of Education Department of Guizhou Province(No.[2022]045)Guizhou University Natural Science Special(special post)Research Fund(No.(2023)17)
文摘Outstanding electric performance can be achieved in the textured ceramics.Therefore,the Ba_(0.85)Ca_(0.15)Zr_(0.09)Ti_(0.91)O_(3)(BCZT)lead-free piezoceramics with high texture degree(f)in<001>direction were successfully prepared using template grain growth method.On account of the perfect sheet BaTiO3(BT)templates,a texture degree as high as 97.9%for BCZT-3.0 wt%BT ceramics was obtained.The ceramics system exhibited excellent comprehensive electrical properties(d_(33)~575 pCN^(-1),k_(p)~0.61,T_(C)~89℃ε_(r)(20℃)~3002,tanδ~4.18%,P_(r)~10.91μC cm^(-2),E_(C)~2.20 kV cm^(-1)).The superior performance originated from the coexistence of rhombohedralorthorhombic-tetragonal phases(R-O-T),as well as high textured degree.The multiphase coexistence was attributed to the composition design.This work provides a theoretical basis for designing lead-free piezoceramics with excellent properties in the future.
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 No.52405414)the China Postdoctoral Science Foundation(Grant No.2024M762580)+1 种基金Young Talent Fund of Xi'an Association for Science and Technology(Grant No.0959202513033)the Youth Innovation Team of Shaanxi Universities,and the Fundamental Research Funds for Central Universities.The authors gratefully acknowledge the support by the Instrumental Analysis Center of Xi’an Jiaotong University for sample characterization.
文摘In the background of carbon neutrality,monolithic ceramic catalysts are universally used in energy conversion and chemical catalysis due to the high heat and mass transfer efficiencies,low bed pressures,and scalability through modular design.However,traditional manufacturing processes are limited by mold dependence,organic solvent toxicity,and insufficient molding capability for complex structures,resulting in difficulty achieving precise regulation of cross-scale pores.Additive manufacturing(AM)technology employs a digital layered molding strategy to achieve the cross-scale structural regulation of catalysts from macroscopic flow channels to mesopores and micropores.This paper summarizes recent advances in the structural design of monolithic catalysts enabled by AM technologies and highlights their emerging applications in catalytic processes.Structurally,AM-fabricated monoliths have been effectively employed in key chemical reactions such as fuel reforming,CO_(2)conversion,biofuel synthesis.Strategies such as geometrical topology optimization,multi-scale pore synergy,biomimetic structural design,and functional gradient integration have been utilized to enhance heat and mass transport,reduce pressure drops,and improve overall catalytic performance.By overcoming the limitations of traditional catalysts,AM technologies create a new paradigm for addressing the longstanding challenge of coupling mass transfer with reaction kinetics.This approach provides a feasible pathway for driving both theoretical innovation and practical implementation of high-efficiency catalytic systems.
