(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
A high-entropy matrix with highly polarizable elements sharing a rare-earth element at the same crystallographic site was designed using the chemical formula Ba_(1/5)Pb_(1/5)Sr_(1/5)RE_(1/5)K_(1/5)TiO_(3)(BPSREKTO),wh...A high-entropy matrix with highly polarizable elements sharing a rare-earth element at the same crystallographic site was designed using the chemical formula Ba_(1/5)Pb_(1/5)Sr_(1/5)RE_(1/5)K_(1/5)TiO_(3)(BPSREKTO),where rare-earth(RE)=La,Nb,Sm,Gd,Dy,Ho,Y,and Lu.Single-phase stability was observed only in the BPSREKTO with RE=La,Nd,and Sm high-entropy compounds.The crystal structure,optical properties,and ferroelectric nature of the single-phase ceramic compounds were investigated.Elemental and structural analyses revealed that all the cations were homogeneously distributed in a global centrosymmetric cubic structure(S.G.Pm3m).Optical absorption showed that the RE=Nd compound is more photoactive in the 200-1000 nm wavelength range,unlike the RE=La,Sm high-entropy compounds.The introduction of RE elements in high-entropy ceramic(HEC)systems affects the indirect bandgap of BPSREKTO with RE=La,Nd,and Sm.It was also found that cationic disorder increases the Urbach energy,leading to a decrease in the indirect energy bandgap in the HEC compound compared to the homologue BaTiO_(3)/SrTiO_(3) single-phase.The dielectric spectra show a broad peak in the dielectric constant and dielectric loss,which are shifted in temperatures with increasing frequencies due to a relaxor ferroelectric transition typical of the diffuse phase transitions.This relaxor behavior was unexpected,because the global crystal structure was centrosymmetric,implying an increase in the number of polar nanoregions(PNRs).These PNRs coexisting with non-polar regions(NPRs)were observed using piezo-force microscopy.Furthermore,the slim polarization loop confirmed the relaxor behavior of BPSREKTO with RE=La,Nd,and Sm.These ferroelectric features make these RE-modified HEC materials good candidates for high-energy storage applications.展开更多
Fine grains and slow grain growth rate are beneficial to preventing the thermal stress-induced cracking and thermal conductivity increase of thermal barrier coatings.Inspired by the sluggish diffusion effect of high-e...Fine grains and slow grain growth rate are beneficial to preventing the thermal stress-induced cracking and thermal conductivity increase of thermal barrier coatings.Inspired by the sluggish diffusion effect of high-entropy materials,a novel high-entropy(HE)rare-earth zirconate solid solution(La0.2Ce0.2Nd0.2Sm0.2Eu0.2)2 Zr2 O7 was designed and successfully synthesized in this work.The as-synthesized(La0.2Ce0.2Nd0.2Sm0.2Eu0.2)2 Zr2 O7 is phase-pure with homogeneous rare-earth element distribution.The thermal conductivity of as-synthesized(La0.2Ce0.2Nd0.2Sm0.2Eu0.2)2 Zr2 O7 at room temperature is as low as 0.76 W m^-1 K^-1.Moreover,after being heated at 1500℃for 1-18 h,the average grain size of(La0.2Ce0.2Nd0.2Sm0.2Eu0.2)2 Zr2 O7 only increases from 1.69μm to 3.92μm,while the average grain size of La2Zr2O7 increases from 1.96μm to 8.89μm.Low thermal conductivity and sluggish grain growth rate indicate that high-entropy(La0.2Ce0.2Nd0.2Sm0.2Eu0.2)2Zr2O7 is suitable for application as a thermal barrier coating material and it may possess good thermal stress-induced cracking resistance.展开更多
The introduction of porous structures into high-entropy ceramics is expected to further improve its thermal insulation performance.In this work,a series of novel rare-earth-niobate high-entropy ceramic foams((Dy_(0.2)...The introduction of porous structures into high-entropy ceramics is expected to further improve its thermal insulation performance.In this work,a series of novel rare-earth-niobate high-entropy ceramic foams((Dy_(0.2)Ho_(0.2)Y_(0.2)Er_(0.2)Yb_(0.2))_(3)NbO_(7))with hierarchical pore structures were prepared by a particle-stabilized foaming method.Atomic-scale analysis reveals that high entropy causes atom displacement and lattice distortion.The high-entropy ceramic foams exhibit high porosity(90.13%-96.13%)and ultralow thermal conductivity(0.0343-0.0592 W/(m·K))at room temperature.High-entropy ceramic foam prepared by a 20 wt%slurry sintered at 1500℃has the porosity of 96.12%and extremely low thermal conductivity of 0.0343 W/(m·K).The existence of walls and secondary pores contributes to reduced thermal conductivity.There is a temperature difference of over 800℃between frontside and backside of the sample under fire resistance test.The research indicates that these as-prepared high-entropy ceramic foams are expected to be promising thermal insulation materials.展开更多
As an important A_(2)B_(2)O_(7)-type ceramic,(La_(0.2)Nd_(0.2)Sm_(0.2)Gd_(0.2)Eu_(0.2))_(2)Zr_(2)O_(7)high-entropy pyrochlore pos-sesses promising properties such as high melting point,high chemical durability,and low...As an important A_(2)B_(2)O_(7)-type ceramic,(La_(0.2)Nd_(0.2)Sm_(0.2)Gd_(0.2)Eu_(0.2))_(2)Zr_(2)O_(7)high-entropy pyrochlore pos-sesses promising properties such as high melting point,high chemical durability,and low thermal conductivity.However,the low sintering ability limits its application in thermal barrier coating and radioactive waste immobilization.It usually needs long-term high-temperature soaking to achieve full density,but with inevitable grain growth.In this work,dense and grain-refined nanocrystalline(La_(0.2)Nd_(0.2)Sm_(0.2)Gd_(0.2)Eu_(0.2))_(2)Zr_(2)O_(7)ceramics were prepared with ultra-high pressure sintering(UHPS)method under 10 GPa at a low temperature of 800℃.The densification behavior,microstructure evo-lution,and properties of the UHPS-ed samples were then investigated.The grain size of as-prepared(La_(0.2)Nd_(0.2)Sm_(0.2)Gd_(0.2)Eu_(0.2))_(2)Zr_(2)O_(7)ceramic was only 151 nm,which is 40%smaller than that of raw pow-der.In addition,it exhibited advantageous properties including both high hardness and aqueous durabil-ity.Plastic deformation under ultra-high pressure was believed as the dominant densification mechanism responsible for grain refinement and property improvement.展开更多
In this work,C_(f)/(CrZrHfNbTa)C-SiC high-entropy ceramic matrix composites with good load-bearing,elec-tromagnetic shielding and ablation resistance were designed and reported for the first time.The compos-ites were ...In this work,C_(f)/(CrZrHfNbTa)C-SiC high-entropy ceramic matrix composites with good load-bearing,elec-tromagnetic shielding and ablation resistance were designed and reported for the first time.The compos-ites were fabricated by an efficient combined processing of slurry infiltration lamination(SIL)and precur-sor infiltration and pyrolysis(PIP).Density and porosity of the as-fabricated composites are 2.72 g/cm^(3) and 12.44 vol.%,respectively,and the flexural strength is 185±13 MPa.Due to the carbon fiber rein-forcement with high conductivity and strong reflection,and high-entropy(CrZrHfNbTa)C ceramic matrix with strong absorbability,the total Electromagnetic interference shielding efficiency(SET)of the compos-ites with a thickness of 3 mm are as high as 88.2 dB and 90 dB respectively in X-band and Ku-band.This means that higher than 99.999999%electromagnetic shielding is achieved at 8-18 GHz,showing excel-lent electromagnetic shielding performance.The C_(f)/(CrZrHfNbTa)C-SiC composites also present excellent ablation resistance,with the linear and mass ablation rates of 0.9μm/s and 1.82 mg/s after ablation at the heat flux of 5 MW/m^(2) for 300 s(∼2450℃).This work opens a new insight for the synergistic de-sign of structural and functional integrated materials with load-bearing,electromagnetic shielding and ablation resistance,etc.展开更多
High-entropy ceramics are new single-phase materials with at least four cation or anion types.Their large configurational entropy is believed to enhance the simultaneous solubility of many components,which can be used...High-entropy ceramics are new single-phase materials with at least four cation or anion types.Their large configurational entropy is believed to enhance the simultaneous solubility of many components,which can be used to optimize certain properties.In this work,a high-entropy oxide,Li(Gd_(0.2)Ho_(0.2)Er_(0.2)Yb_(0.2)Lu_(0.2))GeO_(4)(LRG)was explored as a microwave dielectric ceramic for lowtemperature cofired ceramic technologies.The LRG high-entropy ceramic with an olivine structure formed in the sintering temperature range of 1020-1100℃.The minimal distortion(5×10^(-4))of the[RO_(6)]octahedron led to a stable temperature coefficient of resonant frequency(τf)of-5.3 to-2.9 ppm/℃.Optimal microwave dielectric properties were achieved in the high-entropy ceramics at 1080℃ for 4 h with a relative density of 94.9%,a relative permittivity(ε_(r))of 7.2,and a quality factor(Q×f)of 29000 GHz(at15.3 GHz).For low-temperature cofired ceramic technology applications,the sintering temperature of the LRG high-entropy ceramic was reduced to 900℃ by the addition of 3 wt%H_(3)BO_(3),which exhibited outstanding microwave dielectric properties(ε_(r)=7.6,Q×f=11700 GHz,and τ_(f)=-7.4 ppm/℃)and a good chemical compatibility with silver.展开更多
Single-phase Ba(Ti_(0.2)Zr_(0.2)Sn_(0.2)Hf_(0.2)Ce_(0.2))O_(3)(BTZSHC) high-entropy ceramics(HECs) with the perovskite structure were successfully prepared via the sol-gel method.The results reveal that the as-prepare...Single-phase Ba(Ti_(0.2)Zr_(0.2)Sn_(0.2)Hf_(0.2)Ce_(0.2))O_(3)(BTZSHC) high-entropy ceramics(HECs) with the perovskite structure were successfully prepared via the sol-gel method.The results reveal that the as-prepared ceramics exhibit a single cubic phase belonging to the Pm3 m space group.The high entropy is the driving force of the formation of single-phase ceramics.A larger entropy(ΔS_(mix)) and a negative enthalpy(ΔH_(mix)) are conducive to the formation of single-phase compounds.Herein,ΔS_(mix)=0.323 R mole-1andΔH_(mix)=43.88 kJ/mol.The sluggish-diffusion effect ensures the thermal stability of high-entropy systems.Dielectric measurements reveal that the as-prepared BTZSHC high-entropy ceramics are relaxor ferroelectrics,and the degree of relaxor(γ) is 1.9.The relaxor behavior of the as-prepared ceramics can be ascribed to the relaxation and thermal evolution of their polar units(PUs).The findings of this work provide a theoretical basis and technical support for the preparation of single-phase high-entropy ceramics.展开更多
The electrical properties of high-entropy ceramics(HECs)have been extensively studied in recent years due to their unique structural characteristics and fascinating functional properties induced by entropy engineering...The electrical properties of high-entropy ceramics(HECs)have been extensively studied in recent years due to their unique structural characteristics and fascinating functional properties induced by entropy engineering.Novel high-entropy(Sm_(0.2)Eu_(0.2)Gd_(0.2)Ho_(0.2)Yb_(0.2))CrO_(3)(HE-RECrO_(3))nanofibers were prepared by electro spinning.This work demonstrates that HE-RECrO_(3)nanofibe rs were successfully synthesized at a low temperature(800℃),which is approximately 400℃lower than the temperatures at which chromate ceramics were synthesized via the sol-gel method and the solid-state reaction method.The resistivity of HE-RECrO_(3)nanofibers decreases exponentially with increasing temperature from 25 to600℃.The logarithm of the resistivity is linearly related to the inverse of the temperature,confirming the negative temperature coefficient property of HE-RECrO_(3)nanofibers.The B_(25/50)value of the HERECrO_(3)nanofibers reaches 4072 K.In conclusion,HE-RECrO_(3)nanofibers are expected to be potential candidates for negative-temperature-coefficient(NTC)thermistors.展开更多
The grain growth kinetics and densification mechanism of(TiZrHfVNbTa)C high-entropy carbide ceramic are investigated in this work.A single phase carbide with a rock-salt structure is formed until 2300°C,below whi...The grain growth kinetics and densification mechanism of(TiZrHfVNbTa)C high-entropy carbide ceramic are investigated in this work.A single phase carbide with a rock-salt structure is formed until 2300°C,below which an apparent aggregation of V,Zr and Hf exists.It is associated with the slow diffusion rate of V element as well as the relatively poor solubility of VC in HfC(as well as ZrC).The grain growth mechanism gradually changes from surface diffusion to volume diffusion and then grain boundary diffusion with increasing sintering temperature.This is attributed to the variation of activation energy of grain growth.The densification mechanism is principally dominated by the mass transport through lattice diffusion with the activation energy of 839±53 k J/mol.Through the design of two-step sintering,it is verified that the solid solution formation can effectively promote the densification process.展开更多
A high-entropy(Ti Zr Nb Ta Mo)C ceramic has been successfully fabricated by hot pressing the newlysynthesized quinary carbide powder to investigate its microstructure and mechanical properties.The carbothermal reducti...A high-entropy(Ti Zr Nb Ta Mo)C ceramic has been successfully fabricated by hot pressing the newlysynthesized quinary carbide powder to investigate its microstructure and mechanical properties.The carbothermal reduction process of equimolar quinary metallic oxides at 1500℃for 1 h generates a carbide powder mixture,which consists mainly of Ta C-and Zr C-based solid solutions.The as-synthesized powder was then sintered to form a single-phase high-entropy ceramic by a two-step hot pressing at 1850℃for1 h and 2100℃for 0.5 h,respectively.The high-entropy ceramic exhibits a fine grain size of about 8.8μm,a high compositional uniformity and a high relative density of 98.6%by adding Mo as the strategic main component.The measured nanohardness values of(TiZrNbTaMo)C ceramic are 25.3 GPa at 9.8 N and 31.3 GPa at 100 m N,respectively,which are clearly higher than those of other available high-entropy carbide ceramics.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
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
A series of single-phase high-entropy perovskite ceramics(HEPCs)(La_(0.25)Nd_(0.25)Sm_(0.25)Gd_(0.25))_(1-x)Yb_(x)MnO_(3)(x=0.25,0.3,0.35 and 0.4)was synthesized using solid-state reactions.The effect of Yb on the str...A series of single-phase high-entropy perovskite ceramics(HEPCs)(La_(0.25)Nd_(0.25)Sm_(0.25)Gd_(0.25))_(1-x)Yb_(x)MnO_(3)(x=0.25,0.3,0.35 and 0.4)was synthesized using solid-state reactions.The effect of Yb on the structure and magnetic properties was systematically investigated.The results show that all samples are in orthorhombic perovskite structures with a space group of Pbnm and exhibit a strong crystallization trend sintered at 1300℃for 16 h.All HEPCs have a smooth surface morphology with distinct grain boundaries and exhibit significant hysteresis effects at T=5 K.With the increase of Yb,high lattice distortion and weak double exchange lead to the decrease of T_(C).The presence of Jahn-Teller(JT)distortion and the enhancement of MnO_(6)octahedral distortion result in different magnetic interactions.Moreover,the sample has the best magnetic properties at x=0.35 among the four HEPCs,which is attributed to the large content of Mn^(3+),remnant ratio(Mr/Ms)and lattice distortion(σ^(2)).This work provides a valuable reference for regulating the magnetism of high-entropy ceramics based on rare-earth perovskite manganese oxides.展开更多
The highly transparent novel high-entropy(Lu_(0.2)Y_(0.2)Gd_(0.2)Yb_(0.2)Er_(0.2))_(2)O_(3) ceramic was successfully fabri-cated by the addition of 3 at.%ZrO_(2) and 10 at.%La_(2)O_(3) introduced as sintering additive...The highly transparent novel high-entropy(Lu_(0.2)Y_(0.2)Gd_(0.2)Yb_(0.2)Er_(0.2))_(2)O_(3) ceramic was successfully fabri-cated by the addition of 3 at.%ZrO_(2) and 10 at.%La_(2)O_(3) introduced as sintering additives via vacuum sin-tering.A single-phase solid solution cubic structure of the ceramic was obtained with a relative density of 99.95%and an average grain size of 6.91±3.28μm.The grain boundary of the(Lu_(0.2)Y_(0.2)Gd_(0.2)Yb_(0.2)Er_(0.2))_(2)O_(3) ceramic was clean with a thickness of only 1.3 nm.Further observations revealed uniform distribu-tion of all elements in the grains,and the presence of La and Zr segregation(1.5 nm thick)at few grain boundaries,but causing very little light scattering.The in-line transmittance of high-entropy(Lu_(0.2)Y_(0.2)Gd_(0.2)Yb_(0.2)Er_(0.2))_(2)O_(3) ceramic reached 80%at 1100 nm,which was 98.7%of the theoretical value of Er_(2)O_(3) single crystal.Also,there were fluorescence emissions observed in the ultraviolet(311 nm),vis-ible(563,622 nm),and near-infrared(1032,1535 nm)regions.In addition,the intense red emission and weak green emission were detected,and the broad emission with a peak at 1.5μm was attributed to Stark splitting of Er3+ions,so the corresponding mechanism was discussed.Results obtained suggest that the highly transparent novel high-entropy(Lu_(0.2)Y_(0.2)Gd_(0.2)Yb_(0.2)Er_(0.2))_(2)O_(3) ceramic fabricated in this study could have broad application prospects in optical applications such as scintillators,up-conversion luminescent materials,and infrared lasers.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
Ceramic aerogels(CAs)have emerged as a significant research frontier across various applications due to their lightweight,high porosity,and easily tunable structural characteristics.However,the intrinsic weak interact...Ceramic aerogels(CAs)have emerged as a significant research frontier across various applications due to their lightweight,high porosity,and easily tunable structural characteristics.However,the intrinsic weak interactions among the constituent nanoparticles,coupled with the limited toughness of traditional CAs,make them susceptible to structural collapse or even catastrophic failure when exposed to complex mechanical external forces.Unlike 0D building units,1D ceramic nanofibers(CNFs)possess a high aspect ratio and exceptional flexibility simultaneously,which are desirable building blocks for elastic CAs.This review presents the recent progress in electrospun ceramic nanofibrous aerogels(ECNFAs)that are constructed using ECNFs as building blocks,focusing on the various preparation methods and corresponding structural characteristics,strategies for optimizing mechanical performance,and a wide range of applications.The methods for preparing ECNFs and ECNFAs with diverse structures were initially explored,followed by the implementation of optimization strategies for enhancing ECNFAs,emphasizing the improvement of reinforcing the ECNFs,establishing the bonding effects between ECNFs,and designing the aggregate structures of the aerogels.Moreover,the applications of ECNFAs across various fields are also discussed.Finally,it highlights the existing challenges and potential opportunities for ECNFAs to achieve superior properties and realize promising prospects.展开更多
FeCoCrMnNiN_(x)high entropy nitride ceramics thin films were prepared using the magnetron sputtering method,and the effects of nitrogen content on the thin films’properties were later examined.The addition of N_(2)af...FeCoCrMnNiN_(x)high entropy nitride ceramics thin films were prepared using the magnetron sputtering method,and the effects of nitrogen content on the thin films’properties were later examined.The addition of N_(2)affected the microstructures of the thin films and their mechanical and corrosion properties.Compared with the FeCoCrMnNi thin films with 1-sccm N_(2),the addition of 2 and 3 sccm of N_(2)by as much as 5.45at%and 6.34at%changed the solid solution’s crystalline structure into an amorphous structure.The addition of nitro-gen caused drastic changes to the surface morphology,creating a smoother and more uniform surface without cauliflower units.The atomic force microscopy image analysis indicated that the addition of nitrogen reduced the surface roughness from 5.58 to 1.82 nm.Adding N_(2)to the CoCrFeMnNi thin film helped increase its mechanical properties,such as hardness and strength,while the Young’s modulus decreased.The hardness of(8.75±0.5)GPa and the reduced Young’s modulus of(257.37±11.4)GPa of the FeCoCrMnNi thin film reached(12.67±1.2)and(194.39±12.4)GPa,respectively,with 1 sccm N_(2).The applied coating of the CoCrFeMnNi thin film on 304SUS increased the corrosion resistance,whereas the addition of nitrogen to the CoCrFeMnNi thin film also improved its corrosion res-istance compared with that of the CoCrFeMnNi thin film without nitrogen.展开更多
In a rapid cycling synchrotron(RCS),the magnetic field is synchronized with the beam energy,creating a highly dynamic magnetic environment.A ceramic chamber with a shielding layer(RF shield),composed of a series of co...In a rapid cycling synchrotron(RCS),the magnetic field is synchronized with the beam energy,creating a highly dynamic magnetic environment.A ceramic chamber with a shielding layer(RF shield),composed of a series of copper strips connected to a capacitor at either end,is typically employed as a vacuum chamber to mitigate eddy current effects and beam coupling impedance.Consequently,the ceramic chamber exhibits a thin-walled multilayered complex structure.Previous theoretical studies have suggested that the impedance of such a structure has a negligible impact on the beam.However,recent impedance measurements of the ceramic chamber in the China Spallation Neutron Source(CSNS)RCS revealed a resonance in the low-frequency range,which was confirmed by further theoretical analysis as a source of beam instability in the RCS.Currently,the magnitude of this impedance cannot be accurately assessed using theoretical calculations.In this study,we used the CST Microwave Studio to confirm the impedance of the ceramic chamber.Further simulations covering six different types of ceramic chambers were conducted to develop an impedance model in the RCS.Additionally,this study investigates the resonant characteristics of the ceramic chamber impedance,finding that the resonant frequency is closely related to the capacitance of the capacitors.This finding provides clear directions for further impedance optimization and is crucial for achieving a beam power of 500 kW for the CSNS Phase-Ⅱ project(CSNS-Ⅱ).However,careful attention must be paid to the voltage across the capacitors.展开更多
As a 3D printing method,laser powder bed fusion(LPBF)technology has been extensively proven to offer significant advantages in fabricating complex structured specimens,achieving ultra-fine microstructures,and enhancin...As a 3D printing method,laser powder bed fusion(LPBF)technology has been extensively proven to offer significant advantages in fabricating complex structured specimens,achieving ultra-fine microstructures,and enhancing performances.In the domain of manufacturing melt-grown oxide ceramics,it encounters substantial challenges in suppressing crack defects during the rapid solidification process.The strategic integration of high entropy alloys(HEA),leveraging the significant ductility and toughness into ceramic powders represents a major innovation in overcoming the obstacles.The ingenious doping of HEA parti-cles preserves the eutectic microstructures of the Al_(2)O_(3)/GdAlO_(3)(GAP)/ZrO_(2)ceramic composite.The high damage tolerance of the HEA alloy under high strain rates enables the absorption of crack energy and alleviation of internal stresses during LPBF,effectively reducing crack initiation and growth.Due to in-creased curvature forces and intense Marangoni convection at the top of the molt pool,particle collision intensifies,leading to the tendency of HEA particles to agglomerate at the upper part of the molt pool.However,this phenomenon can be effectively alleviated in the remelting process of subsequent layer de-position.Furthermore,a portion of the HEA particles partially dissolves and sinks into the molten pool,acting as heterogeneous nucleation particles,inducing the formation of equiaxed eutectic and leading pri-mary phase nucleation.Some HEA particles diffuse into the lamellar ternary eutectic structures,further promoting the refinement of eutectic microstructures due to increased undercooling.The innovative dop-ing of HEA particles has effectively facilitated the fabrication of turbine-structured,conical,and cylindrical ternary eutectic ceramic composite specimens with diameters of about 70 mm,demonstrating significant developmental potential in the field of ceramic composite manufacturing.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.
基金the National Autonomous University of México(UNAM)through the Support Program for Technological Research and Innovation Projects(DGAPAPAPIIT),grants No.IN103623.
文摘A high-entropy matrix with highly polarizable elements sharing a rare-earth element at the same crystallographic site was designed using the chemical formula Ba_(1/5)Pb_(1/5)Sr_(1/5)RE_(1/5)K_(1/5)TiO_(3)(BPSREKTO),where rare-earth(RE)=La,Nb,Sm,Gd,Dy,Ho,Y,and Lu.Single-phase stability was observed only in the BPSREKTO with RE=La,Nd,and Sm high-entropy compounds.The crystal structure,optical properties,and ferroelectric nature of the single-phase ceramic compounds were investigated.Elemental and structural analyses revealed that all the cations were homogeneously distributed in a global centrosymmetric cubic structure(S.G.Pm3m).Optical absorption showed that the RE=Nd compound is more photoactive in the 200-1000 nm wavelength range,unlike the RE=La,Sm high-entropy compounds.The introduction of RE elements in high-entropy ceramic(HEC)systems affects the indirect bandgap of BPSREKTO with RE=La,Nd,and Sm.It was also found that cationic disorder increases the Urbach energy,leading to a decrease in the indirect energy bandgap in the HEC compound compared to the homologue BaTiO_(3)/SrTiO_(3) single-phase.The dielectric spectra show a broad peak in the dielectric constant and dielectric loss,which are shifted in temperatures with increasing frequencies due to a relaxor ferroelectric transition typical of the diffuse phase transitions.This relaxor behavior was unexpected,because the global crystal structure was centrosymmetric,implying an increase in the number of polar nanoregions(PNRs).These PNRs coexisting with non-polar regions(NPRs)were observed using piezo-force microscopy.Furthermore,the slim polarization loop confirmed the relaxor behavior of BPSREKTO with RE=La,Nd,and Sm.These ferroelectric features make these RE-modified HEC materials good candidates for high-energy storage applications.
基金financially supported by the National Natural Science Foundation of China (Nos.51672064 and U1435206)
文摘Fine grains and slow grain growth rate are beneficial to preventing the thermal stress-induced cracking and thermal conductivity increase of thermal barrier coatings.Inspired by the sluggish diffusion effect of high-entropy materials,a novel high-entropy(HE)rare-earth zirconate solid solution(La0.2Ce0.2Nd0.2Sm0.2Eu0.2)2 Zr2 O7 was designed and successfully synthesized in this work.The as-synthesized(La0.2Ce0.2Nd0.2Sm0.2Eu0.2)2 Zr2 O7 is phase-pure with homogeneous rare-earth element distribution.The thermal conductivity of as-synthesized(La0.2Ce0.2Nd0.2Sm0.2Eu0.2)2 Zr2 O7 at room temperature is as low as 0.76 W m^-1 K^-1.Moreover,after being heated at 1500℃for 1-18 h,the average grain size of(La0.2Ce0.2Nd0.2Sm0.2Eu0.2)2 Zr2 O7 only increases from 1.69μm to 3.92μm,while the average grain size of La2Zr2O7 increases from 1.96μm to 8.89μm.Low thermal conductivity and sluggish grain growth rate indicate that high-entropy(La0.2Ce0.2Nd0.2Sm0.2Eu0.2)2Zr2O7 is suitable for application as a thermal barrier coating material and it may possess good thermal stress-induced cracking resistance.
基金supported by the National Natural Science Foundation of China(No.52072301)the State Key Laboratory of Solidification Processing(NPU)(No.2021-TS-08)+3 种基金the State Key Laboratory of New Ceramic and Fine Processing Tsinghua University(No.KFZD202102)the China-Poland International Collaboration Fund of National Natural Science Foundation of China(No.51961135301)the Fundamental Research Funds for the Central Universities(No.D5000210722)State Key Laboratory of Materials Processing and Die&Mould Technology,Huazhong University of Science and Technology(No.P2020–009)。
文摘The introduction of porous structures into high-entropy ceramics is expected to further improve its thermal insulation performance.In this work,a series of novel rare-earth-niobate high-entropy ceramic foams((Dy_(0.2)Ho_(0.2)Y_(0.2)Er_(0.2)Yb_(0.2))_(3)NbO_(7))with hierarchical pore structures were prepared by a particle-stabilized foaming method.Atomic-scale analysis reveals that high entropy causes atom displacement and lattice distortion.The high-entropy ceramic foams exhibit high porosity(90.13%-96.13%)and ultralow thermal conductivity(0.0343-0.0592 W/(m·K))at room temperature.High-entropy ceramic foam prepared by a 20 wt%slurry sintered at 1500℃has the porosity of 96.12%and extremely low thermal conductivity of 0.0343 W/(m·K).The existence of walls and secondary pores contributes to reduced thermal conductivity.There is a temperature difference of over 800℃between frontside and backside of the sample under fire resistance test.The research indicates that these as-prepared high-entropy ceramic foams are expected to be promising thermal insulation materials.
基金financially supported by the National Natu-ral Science Foundation of China(nos.92163208,51902233,and 51972243)the National Key Research and Development Plan of China(no.2021YFB3701400)the Independent Innovation Projects of the Hubei Longzhong Laboratory(no.2022ZZ-11).
文摘As an important A_(2)B_(2)O_(7)-type ceramic,(La_(0.2)Nd_(0.2)Sm_(0.2)Gd_(0.2)Eu_(0.2))_(2)Zr_(2)O_(7)high-entropy pyrochlore pos-sesses promising properties such as high melting point,high chemical durability,and low thermal conductivity.However,the low sintering ability limits its application in thermal barrier coating and radioactive waste immobilization.It usually needs long-term high-temperature soaking to achieve full density,but with inevitable grain growth.In this work,dense and grain-refined nanocrystalline(La_(0.2)Nd_(0.2)Sm_(0.2)Gd_(0.2)Eu_(0.2))_(2)Zr_(2)O_(7)ceramics were prepared with ultra-high pressure sintering(UHPS)method under 10 GPa at a low temperature of 800℃.The densification behavior,microstructure evo-lution,and properties of the UHPS-ed samples were then investigated.The grain size of as-prepared(La_(0.2)Nd_(0.2)Sm_(0.2)Gd_(0.2)Eu_(0.2))_(2)Zr_(2)O_(7)ceramic was only 151 nm,which is 40%smaller than that of raw pow-der.In addition,it exhibited advantageous properties including both high hardness and aqueous durabil-ity.Plastic deformation under ultra-high pressure was believed as the dominant densification mechanism responsible for grain refinement and property improvement.
基金supported by the National Key R&D Program of China(no.2022YFB3707700)Program of Shang-hai Academic/Technology Research Leader(no.23XD1424300)National Natural Science Foundation of China(no.52332003).
文摘In this work,C_(f)/(CrZrHfNbTa)C-SiC high-entropy ceramic matrix composites with good load-bearing,elec-tromagnetic shielding and ablation resistance were designed and reported for the first time.The compos-ites were fabricated by an efficient combined processing of slurry infiltration lamination(SIL)and precur-sor infiltration and pyrolysis(PIP).Density and porosity of the as-fabricated composites are 2.72 g/cm^(3) and 12.44 vol.%,respectively,and the flexural strength is 185±13 MPa.Due to the carbon fiber rein-forcement with high conductivity and strong reflection,and high-entropy(CrZrHfNbTa)C ceramic matrix with strong absorbability,the total Electromagnetic interference shielding efficiency(SET)of the compos-ites with a thickness of 3 mm are as high as 88.2 dB and 90 dB respectively in X-band and Ku-band.This means that higher than 99.999999%electromagnetic shielding is achieved at 8-18 GHz,showing excel-lent electromagnetic shielding performance.The C_(f)/(CrZrHfNbTa)C-SiC composites also present excellent ablation resistance,with the linear and mass ablation rates of 0.9μm/s and 1.82 mg/s after ablation at the heat flux of 5 MW/m^(2) for 300 s(∼2450℃).This work opens a new insight for the synergistic de-sign of structural and functional integrated materials with load-bearing,electromagnetic shielding and ablation resistance,etc.
基金financial support from the Shenzhen Basic Research General Program(No.JCYJ20190808114618998)。
文摘High-entropy ceramics are new single-phase materials with at least four cation or anion types.Their large configurational entropy is believed to enhance the simultaneous solubility of many components,which can be used to optimize certain properties.In this work,a high-entropy oxide,Li(Gd_(0.2)Ho_(0.2)Er_(0.2)Yb_(0.2)Lu_(0.2))GeO_(4)(LRG)was explored as a microwave dielectric ceramic for lowtemperature cofired ceramic technologies.The LRG high-entropy ceramic with an olivine structure formed in the sintering temperature range of 1020-1100℃.The minimal distortion(5×10^(-4))of the[RO_(6)]octahedron led to a stable temperature coefficient of resonant frequency(τf)of-5.3 to-2.9 ppm/℃.Optimal microwave dielectric properties were achieved in the high-entropy ceramics at 1080℃ for 4 h with a relative density of 94.9%,a relative permittivity(ε_(r))of 7.2,and a quality factor(Q×f)of 29000 GHz(at15.3 GHz).For low-temperature cofired ceramic technology applications,the sintering temperature of the LRG high-entropy ceramic was reduced to 900℃ by the addition of 3 wt%H_(3)BO_(3),which exhibited outstanding microwave dielectric properties(ε_(r)=7.6,Q×f=11700 GHz,and τ_(f)=-7.4 ppm/℃)and a good chemical compatibility with silver.
基金financially supported by the National Natural Science Foundation of China (Nos.52102144,52172099)the Provincial Joint Fund of Shaanxi (No.2021JLM-28)+1 种基金the Natural Science Basic Research Plan in Shaanxi Province of China (No.2022JM-255)the Scientific Research Plan Projects of Shaanxi Education Department (No.19JK0525)。
文摘Single-phase Ba(Ti_(0.2)Zr_(0.2)Sn_(0.2)Hf_(0.2)Ce_(0.2))O_(3)(BTZSHC) high-entropy ceramics(HECs) with the perovskite structure were successfully prepared via the sol-gel method.The results reveal that the as-prepared ceramics exhibit a single cubic phase belonging to the Pm3 m space group.The high entropy is the driving force of the formation of single-phase ceramics.A larger entropy(ΔS_(mix)) and a negative enthalpy(ΔH_(mix)) are conducive to the formation of single-phase compounds.Herein,ΔS_(mix)=0.323 R mole-1andΔH_(mix)=43.88 kJ/mol.The sluggish-diffusion effect ensures the thermal stability of high-entropy systems.Dielectric measurements reveal that the as-prepared BTZSHC high-entropy ceramics are relaxor ferroelectrics,and the degree of relaxor(γ) is 1.9.The relaxor behavior of the as-prepared ceramics can be ascribed to the relaxation and thermal evolution of their polar units(PUs).The findings of this work provide a theoretical basis and technical support for the preparation of single-phase high-entropy ceramics.
基金Project supported by the National Key Research and Development Program of China(2019YFC0605000)the"Transformational Technologies for Clean Energy and Demonstration",Strategic Priority Research Program of the Chinese Academy of Sciences(XDA21000000)+4 种基金the Independent Deployment Project of Ganjiang Innovation Research Institute of Chinese Academy of Sciences(E055A002)the Independent Deployment Project of China Fujian Innovation Laboratory of Optoelectronic Information Technology(2021ZZ109)the Fujian Provincial Natural Fund(2021J05101)the National Natural Science Foundation of China(21771196,62275276)Advanced Energy Science and Technology Guangdong Laboratory(HND20TDGFDC00)。
文摘The electrical properties of high-entropy ceramics(HECs)have been extensively studied in recent years due to their unique structural characteristics and fascinating functional properties induced by entropy engineering.Novel high-entropy(Sm_(0.2)Eu_(0.2)Gd_(0.2)Ho_(0.2)Yb_(0.2))CrO_(3)(HE-RECrO_(3))nanofibers were prepared by electro spinning.This work demonstrates that HE-RECrO_(3)nanofibe rs were successfully synthesized at a low temperature(800℃),which is approximately 400℃lower than the temperatures at which chromate ceramics were synthesized via the sol-gel method and the solid-state reaction method.The resistivity of HE-RECrO_(3)nanofibers decreases exponentially with increasing temperature from 25 to600℃.The logarithm of the resistivity is linearly related to the inverse of the temperature,confirming the negative temperature coefficient property of HE-RECrO_(3)nanofibers.The B_(25/50)value of the HERECrO_(3)nanofibers reaches 4072 K.In conclusion,HE-RECrO_(3)nanofibers are expected to be potential candidates for negative-temperature-coefficient(NTC)thermistors.
基金financially supported by the National Natural Science Foundation of China(Nos.51972081,52032002 and 51872061)Heilongjiang Touyan Team Programthe Foundation of Science and Technology on Particle Transport and Separation Laboratory。
文摘The grain growth kinetics and densification mechanism of(TiZrHfVNbTa)C high-entropy carbide ceramic are investigated in this work.A single phase carbide with a rock-salt structure is formed until 2300°C,below which an apparent aggregation of V,Zr and Hf exists.It is associated with the slow diffusion rate of V element as well as the relatively poor solubility of VC in HfC(as well as ZrC).The grain growth mechanism gradually changes from surface diffusion to volume diffusion and then grain boundary diffusion with increasing sintering temperature.This is attributed to the variation of activation energy of grain growth.The densification mechanism is principally dominated by the mass transport through lattice diffusion with the activation energy of 839±53 k J/mol.Through the design of two-step sintering,it is verified that the solid solution formation can effectively promote the densification process.
基金supported financially by the National Natural Science Foundation of China(Nos.51602074,51872061,51532006 and 51621091)the Natural Science Foundation of Heilongjiang Province(No.E2016026)+1 种基金the China Postdoctoral Science Foundation(No.2016 M600246)the Heilongjiang Postdoctoral Foundation(No.LBH-Z16084).
文摘A high-entropy(Ti Zr Nb Ta Mo)C ceramic has been successfully fabricated by hot pressing the newlysynthesized quinary carbide powder to investigate its microstructure and mechanical properties.The carbothermal reduction process of equimolar quinary metallic oxides at 1500℃for 1 h generates a carbide powder mixture,which consists mainly of Ta C-and Zr C-based solid solutions.The as-synthesized powder was then sintered to form a single-phase high-entropy ceramic by a two-step hot pressing at 1850℃for1 h and 2100℃for 0.5 h,respectively.The high-entropy ceramic exhibits a fine grain size of about 8.8μm,a high compositional uniformity and a high relative density of 98.6%by adding Mo as the strategic main component.The measured nanohardness values of(TiZrNbTaMo)C ceramic are 25.3 GPa at 9.8 N and 31.3 GPa at 100 m N,respectively,which are clearly higher than those of other available high-entropy carbide ceramics.
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Project supported by the Guangxi Natural Science Foundation,China(2024GXNSFAA010415)the Opening Fund of the Key Laboratory of New Processing Technology for Nonferrous Metals&Materials of the Ministry of Education(22AA-9)。
文摘A series of single-phase high-entropy perovskite ceramics(HEPCs)(La_(0.25)Nd_(0.25)Sm_(0.25)Gd_(0.25))_(1-x)Yb_(x)MnO_(3)(x=0.25,0.3,0.35 and 0.4)was synthesized using solid-state reactions.The effect of Yb on the structure and magnetic properties was systematically investigated.The results show that all samples are in orthorhombic perovskite structures with a space group of Pbnm and exhibit a strong crystallization trend sintered at 1300℃for 16 h.All HEPCs have a smooth surface morphology with distinct grain boundaries and exhibit significant hysteresis effects at T=5 K.With the increase of Yb,high lattice distortion and weak double exchange lead to the decrease of T_(C).The presence of Jahn-Teller(JT)distortion and the enhancement of MnO_(6)octahedral distortion result in different magnetic interactions.Moreover,the sample has the best magnetic properties at x=0.35 among the four HEPCs,which is attributed to the large content of Mn^(3+),remnant ratio(Mr/Ms)and lattice distortion(σ^(2)).This work provides a valuable reference for regulating the magnetism of high-entropy ceramics based on rare-earth perovskite manganese oxides.
基金supported by the National Natural Science Foundation of China(No.51832002 and 52072077),Instrumental Analysis Center of Guangdong Unversity of Technology,Sinomate Institute of Materials Research(Guang Zhou)Co.,Ltd(SIMR)for assisting the TEM characterization.
文摘The highly transparent novel high-entropy(Lu_(0.2)Y_(0.2)Gd_(0.2)Yb_(0.2)Er_(0.2))_(2)O_(3) ceramic was successfully fabri-cated by the addition of 3 at.%ZrO_(2) and 10 at.%La_(2)O_(3) introduced as sintering additives via vacuum sin-tering.A single-phase solid solution cubic structure of the ceramic was obtained with a relative density of 99.95%and an average grain size of 6.91±3.28μm.The grain boundary of the(Lu_(0.2)Y_(0.2)Gd_(0.2)Yb_(0.2)Er_(0.2))_(2)O_(3) ceramic was clean with a thickness of only 1.3 nm.Further observations revealed uniform distribu-tion of all elements in the grains,and the presence of La and Zr segregation(1.5 nm thick)at few grain boundaries,but causing very little light scattering.The in-line transmittance of high-entropy(Lu_(0.2)Y_(0.2)Gd_(0.2)Yb_(0.2)Er_(0.2))_(2)O_(3) ceramic reached 80%at 1100 nm,which was 98.7%of the theoretical value of Er_(2)O_(3) single crystal.Also,there were fluorescence emissions observed in the ultraviolet(311 nm),vis-ible(563,622 nm),and near-infrared(1032,1535 nm)regions.In addition,the intense red emission and weak green emission were detected,and the broad emission with a peak at 1.5μm was attributed to Stark splitting of Er3+ions,so the corresponding mechanism was discussed.Results obtained suggest that the highly transparent novel high-entropy(Lu_(0.2)Y_(0.2)Gd_(0.2)Yb_(0.2)Er_(0.2))_(2)O_(3) ceramic fabricated in this study could have broad application prospects in optical applications such as scintillators,up-conversion luminescent materials,and infrared lasers.
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supported by the National Natural Science Foundation of China(Nos.92371110 and 52373281)Weiqiao Science Foundation(H2872302 and H2872303)the Scientific Research Innovation Capability Support Project for Young Faculty.
文摘Ceramic aerogels(CAs)have emerged as a significant research frontier across various applications due to their lightweight,high porosity,and easily tunable structural characteristics.However,the intrinsic weak interactions among the constituent nanoparticles,coupled with the limited toughness of traditional CAs,make them susceptible to structural collapse or even catastrophic failure when exposed to complex mechanical external forces.Unlike 0D building units,1D ceramic nanofibers(CNFs)possess a high aspect ratio and exceptional flexibility simultaneously,which are desirable building blocks for elastic CAs.This review presents the recent progress in electrospun ceramic nanofibrous aerogels(ECNFAs)that are constructed using ECNFs as building blocks,focusing on the various preparation methods and corresponding structural characteristics,strategies for optimizing mechanical performance,and a wide range of applications.The methods for preparing ECNFs and ECNFAs with diverse structures were initially explored,followed by the implementation of optimization strategies for enhancing ECNFAs,emphasizing the improvement of reinforcing the ECNFs,establishing the bonding effects between ECNFs,and designing the aggregate structures of the aerogels.Moreover,the applications of ECNFAs across various fields are also discussed.Finally,it highlights the existing challenges and potential opportunities for ECNFAs to achieve superior properties and realize promising prospects.
基金the Ahvaz Branch, Islamic Azad University for the financial support
文摘FeCoCrMnNiN_(x)high entropy nitride ceramics thin films were prepared using the magnetron sputtering method,and the effects of nitrogen content on the thin films’properties were later examined.The addition of N_(2)affected the microstructures of the thin films and their mechanical and corrosion properties.Compared with the FeCoCrMnNi thin films with 1-sccm N_(2),the addition of 2 and 3 sccm of N_(2)by as much as 5.45at%and 6.34at%changed the solid solution’s crystalline structure into an amorphous structure.The addition of nitro-gen caused drastic changes to the surface morphology,creating a smoother and more uniform surface without cauliflower units.The atomic force microscopy image analysis indicated that the addition of nitrogen reduced the surface roughness from 5.58 to 1.82 nm.Adding N_(2)to the CoCrFeMnNi thin film helped increase its mechanical properties,such as hardness and strength,while the Young’s modulus decreased.The hardness of(8.75±0.5)GPa and the reduced Young’s modulus of(257.37±11.4)GPa of the FeCoCrMnNi thin film reached(12.67±1.2)and(194.39±12.4)GPa,respectively,with 1 sccm N_(2).The applied coating of the CoCrFeMnNi thin film on 304SUS increased the corrosion resistance,whereas the addition of nitrogen to the CoCrFeMnNi thin film also improved its corrosion res-istance compared with that of the CoCrFeMnNi thin film without nitrogen.
基金supported by the Guangdong Basic and Applied Basic Research Foundation,China(No.2021B1515140007).
文摘In a rapid cycling synchrotron(RCS),the magnetic field is synchronized with the beam energy,creating a highly dynamic magnetic environment.A ceramic chamber with a shielding layer(RF shield),composed of a series of copper strips connected to a capacitor at either end,is typically employed as a vacuum chamber to mitigate eddy current effects and beam coupling impedance.Consequently,the ceramic chamber exhibits a thin-walled multilayered complex structure.Previous theoretical studies have suggested that the impedance of such a structure has a negligible impact on the beam.However,recent impedance measurements of the ceramic chamber in the China Spallation Neutron Source(CSNS)RCS revealed a resonance in the low-frequency range,which was confirmed by further theoretical analysis as a source of beam instability in the RCS.Currently,the magnitude of this impedance cannot be accurately assessed using theoretical calculations.In this study,we used the CST Microwave Studio to confirm the impedance of the ceramic chamber.Further simulations covering six different types of ceramic chambers were conducted to develop an impedance model in the RCS.Additionally,this study investigates the resonant characteristics of the ceramic chamber impedance,finding that the resonant frequency is closely related to the capacitance of the capacitors.This finding provides clear directions for further impedance optimization and is crucial for achieving a beam power of 500 kW for the CSNS Phase-Ⅱ project(CSNS-Ⅱ).However,careful attention must be paid to the voltage across the capacitors.
基金supported by the National Natural Science Foundation of China(Nos.52130204,52174376,52202070,51822405)Guangdong Basic and Applied Basic Research Foundation(No.2021B1515120028)+6 种基金TQ Innovation Foundation(No.23-TQ09-02-ZT-01-005)Aeronautical Science Foundation of China(No.20220042053001)Science and Technology Innovation Team Plan of Shaanxi Province(No.2021TD-17)Key R&D Project of Shaanxi Province(No.2024GX-YBXM-220)Thousands Person Plan of Jiangxi Province(JXSQ2020102131)Fundamental Research Funds for the Central Universities(Nos.D5000230348,D5000220057)China Scholarship Council(Nos.202206290133,202306290190).
文摘As a 3D printing method,laser powder bed fusion(LPBF)technology has been extensively proven to offer significant advantages in fabricating complex structured specimens,achieving ultra-fine microstructures,and enhancing performances.In the domain of manufacturing melt-grown oxide ceramics,it encounters substantial challenges in suppressing crack defects during the rapid solidification process.The strategic integration of high entropy alloys(HEA),leveraging the significant ductility and toughness into ceramic powders represents a major innovation in overcoming the obstacles.The ingenious doping of HEA parti-cles preserves the eutectic microstructures of the Al_(2)O_(3)/GdAlO_(3)(GAP)/ZrO_(2)ceramic composite.The high damage tolerance of the HEA alloy under high strain rates enables the absorption of crack energy and alleviation of internal stresses during LPBF,effectively reducing crack initiation and growth.Due to in-creased curvature forces and intense Marangoni convection at the top of the molt pool,particle collision intensifies,leading to the tendency of HEA particles to agglomerate at the upper part of the molt pool.However,this phenomenon can be effectively alleviated in the remelting process of subsequent layer de-position.Furthermore,a portion of the HEA particles partially dissolves and sinks into the molten pool,acting as heterogeneous nucleation particles,inducing the formation of equiaxed eutectic and leading pri-mary phase nucleation.Some HEA particles diffuse into the lamellar ternary eutectic structures,further promoting the refinement of eutectic microstructures due to increased undercooling.The innovative dop-ing of HEA particles has effectively facilitated the fabrication of turbine-structured,conical,and cylindrical ternary eutectic ceramic composite specimens with diameters of about 70 mm,demonstrating significant developmental potential in the field of ceramic composite manufacturing.
