High-entropy ceramics (HECs) are solid solutions of inorganic compounds with one or more Wyckoff sites shared by equal or near-equal atomic ratios of multi-principal elements.Although in the infant stage,the emerging ...High-entropy ceramics (HECs) are solid solutions of inorganic compounds with one or more Wyckoff sites shared by equal or near-equal atomic ratios of multi-principal elements.Although in the infant stage,the emerging of this new family of materials has brought new opportunities for material design and property tailoring.Distinct from metals,the diversity in crystal structure and electronic structure of ceramics provides huge space for properties tuning through band structure engineering and phonon engineering.Aside from strengthening,hardening,and low thermal conductivity that have already been found in high-entropy alloys,new properties like colossal dielectric constant,super ionic conductivity,severe anisotropic thermal expansion coefficient,strong electromagnetic wave absorption,etc.,have been discovered in HECs.As a response to the rapid development in this nascent field,this article gives a comprehensive review on the structure features,theoretical methods for stability and property prediction,processing routes,novel properties,and prospective applications of HECs.The challenges on processing,characterization,and property predictions are also emphasized.Finally,future directions for new material exploration,novel processing,fundamental understanding,in-depth characterization,and database assessments are given.展开更多
The critical requirements for the environmental barrier coating(EBC)materials of silicon-based ceramic matrix composites(CMCs)include good tolerance to harsh environments,thermal expansion matches with the interlayer ...The critical requirements for the environmental barrier coating(EBC)materials of silicon-based ceramic matrix composites(CMCs)include good tolerance to harsh environments,thermal expansion matches with the interlayer mullite,good high-temperature phase stability,and low thermal conductivity.Cuspidine-structured rare-earth aluminates RE_(4)Al_(2)O_(9) have been considered as candidates of EBCs for their superior mechanical and thermal properties,but the phase transition at high temperatures is a notable drawback of these materials.To suppress the phase transition and improve the phase stability,a novel cuspidine-structured rare-earth aluminate solid solution(Nd_(0.2)Sm_(0.2)Eu_(0.2)Y_(0.2)Yb_(0.2))_(4)Al_(2)O_(9) was designed and successfully synthesized inspired by entropy stabilization effect of high-entropy ceramics(HECs).The as-synthesized HE(Nd_(0.2)Sm_(0.2)Eu_(0.2)Y_(0.2)Yb_(0.2))_(4)Al_(2)O_(9) exhibits a close thermal expansion coefficient(6.96×10^(-6) K^(-1) at 300-1473 K)to that of mullite,good phase stability from 300 to 1473 K,and low thermal conductivity(1.50 W·m^(-1)·K^(-1) at room temperature).In addition,strong anisotropic thermal expansion has been observed compared to Y_(4)Al_(2)O_(9) and Yb_(4)Al_(2)O_(9).The mechanism for low thermal conductivity is attributed to the lattice distortion and mass difference of the constituent atoms,and the anisotropic thermal expansion is due to the anisotropic chemical bonding enhanced by the large size rare-earth cations.展开更多
Four high-entropy perovskite(HEP)RETa_(3)O_(9) samples were fabricated via a spark plasma sintering(SPS)method,and the corresponding thermophysical properties and underlying mechanisms were investigated for environmen...Four high-entropy perovskite(HEP)RETa_(3)O_(9) samples were fabricated via a spark plasma sintering(SPS)method,and the corresponding thermophysical properties and underlying mechanisms were investigated for environmental/thermal barrier coating(E/TBC)applications.The prepared samples maintained low thermal conductivity(1.50 W·m^(−1)·K^(−1)),high hardness(10 GPa),and an appropriate Young’s modulus(180 GPa),while the fracture toughness increased to 2.5 MPa·m^(1/2).Nanoindentation results showed the HEP ceramics had excellent mechanical properties and good component homogeneity.We analysed the influence of different parameters(the disorder parameters of the electronegativity,ionic radius,and atomic mass,as well as the tolerance factor)of A-site atoms on the thermal conductivity.Enhanced thermal expansion coefficients,combined with a high melting point and extraordinary phase stability,expanded the applications of the HEP RETa_(3)O_(9).The results of this study had motivated a follow-up study on tantalate high-entropy ceramics with desirable properties.展开更多
Rational design of solid-state electrolytes(SSEs)with high ionic conductivity and low activation energy(Ea)is vital for all solid-state batteries.Machine learning(ML)techniques have recently been successful in predict...Rational design of solid-state electrolytes(SSEs)with high ionic conductivity and low activation energy(Ea)is vital for all solid-state batteries.Machine learning(ML)techniques have recently been successful in predicting Li^(+) conduction property in SSEs with various descriptors and accelerating the development of SSEs.In this work,we extend the previous efforts and introduce a framework of ML prediction for E_(a) in SSEs with hierarchically encoding crystal structure-based(HECS)descriptors.Taking cubic Li-argyrodites as an example,an Ea prediction model is developed to the coefficient of determination(R^(2))and rootmean-square error(RMSE)values of 0.887 and 0.02 eV for training dataset,and 0.820 and 0.02 eV for test dataset,respectively by partial least squares(PLS)analysis,proving the prediction power of HECSdescriptors.The variable importance in projection(VIP)scores demonstrate the combined effects of the global and local Li^(+) conduction environments,especially the anion size and the resultant structural changes associated with anion site disorder.The developed E_(a) prediction model directs us to optimize and design new Li-argyrodites with lower Ea,such as Li_(6–x)PS_(5–x)Cl_(1+x)(<0.322 eV),Li_(6+x)PS_(5+x)Br_(1–x)(<0.273 eV),Li_(6+x)PS_(5+x)Br_(0.25)I_(0.75–x)(<0.352 eV),Li_(6+(5–n)y)P_(1–y)N_(y)S_(5)I(<0.420 eV),Li_(6+(5–n)y)As_(1–y)N_(y)S_(5)I(<0.371 eV),Li_(6+(5–n)y)As_(1–y)NySe_(5)I(<0.450 eV),by broadening bottleneck size,invoking site disorder and activating concerted Li+conduction.This analysis shows great potential in promoting rational design of advanced SSEs and the same approach can be applied to other types of materials.展开更多
Ferrites are the most widely used microwave absorbing materials to deal with the threat of electromagnetic(EM)pollution.However,the lack of sufficient dielectric loss capacity is the main challenge that limits their a...Ferrites are the most widely used microwave absorbing materials to deal with the threat of electromagnetic(EM)pollution.However,the lack of sufficient dielectric loss capacity is the main challenge that limits their applications.To cope with this challenge,three high-entropy(HE)spineltype ferrite ceramics including(Mg_(0.2)Mn_(0.2)Fe_(0.2)Co_(0.2)Ni_(0.2))Fe_(2)O_(4),(Mg_(0.2)Fe_(0.2)Co_(0.2)Ni_(0.2)Cu_(0.2))Fe_(2)O_(4),and(Mg_(0.2)Fe_(0.2)Co_(0.2)Ni_(0.2)Zn_(0.2))Fe_(2)O_(4)were designed and successfully prepared through solid state synthesis.The results show that all three HE MFe_(2)O_(4) samples exhibit synergetic dielectric loss and magnetic loss.The good magnetic loss ability is due to the presence of magnetic components;while the enhanced dielectric properties are attributed to nano-domain,hopping mechanism of resonance effect and HE effect.Among three HE spinels,(Mg_(0.2)Mn_(0.2)Fe_(0.2)Co_(0.2)Ni_(0.2))Fe_(2)O_(4)shows the best EM wave absorption performance,e.g.,its minimum reflection loss(RL_(min))reaches-35.10 dB at 6.78 GHz with a thickness of 3.5 mm,and the optimized effective absorption bandwidth(EAB)is 7.48 GHz from 8.48 to 15.96 GHz at the thickness of 2.4 mm.Due to the easy preparation and strong EM dissipation ability,HE MFe_(2)O_(4) are promising as a new type of EM absorption materials.展开更多
Rare-earth phosphates(REPO4)are regarded as one of the promising thermal/environmental barrier coating(T/EBC)materials for SiCf/SiC ceramic matrix composites(SiC-CMCs)owing to their excellent resistance to water vapor...Rare-earth phosphates(REPO4)are regarded as one of the promising thermal/environmental barrier coating(T/EBC)materials for SiCf/SiC ceramic matrix composites(SiC-CMCs)owing to their excellent resistance to water vapor and CaO–MgO–Al_(2)O_(3)–SiO_(2)(CMAS).Nevertheless,a relatively high thermal conductivity(κ)of the REPO_(4) becomes the bottleneck for their practical applications.In this work,novel xenotime-type high-entropy(Dy_(1/7)Ho_(1/7)Er_(1/7)Tm_(1/7)Yb_(1/7)Lu_(1/7)Y_(1/7))PO4(HE(7RE_(1/7))PO_(4))has been designed and synthesized for the first time to solve this issue.HE(7RE_(1/7))PO_(4) with a homogeneous rare-earth element distribution exhibits high thermal stability up to 1750℃and good chemical compatibility with SiO_(2) up to 1400℃.In addition,the thermal expansion coefficient(TEC)of HE(7RE_(1/7))PO_(4)(5.96×10^(−6)℃^(−1) from room temperature(RT)to 900℃)is close to that of the SiC-CMCs.What is more,the thermal conductivities of HE(7RE_(1/7))PO_(4)(from 4.38 W·m^(−1)·K^(−1) at 100℃to 2.25 W·m^(−1)·K^(−1) at 1300℃)are significantly decreased compared to those of single-component REPO4 with the minimum value ranging from 9.90 to 4.76 W·m^(−1)·K^(−1).These results suggest that HE(7RE_(1/7))PO_(4) has the potential to be applied as the T/EBC materials for the SiC-CMCs in the future.展开更多
The challenge in synthesizing high-entropy ceramic(HEC)nanopowders is to suppress severe grain coarsening and particle agglomeration,which occur at elevated temperatures.This challenge could be addressed by the polyac...The challenge in synthesizing high-entropy ceramic(HEC)nanopowders is to suppress severe grain coarsening and particle agglomeration,which occur at elevated temperatures.This challenge could be addressed by the polyacrylamide gel method.In this work,single-phase high-entropy(Lao.2Ndo.2Smo.2Gdo.2 Ybo.2)2Zr2O7 and(Lao.2Ndo.2Yo.2Euo.2Gdo.2)2Zr2O7 nanopowders without agglomeration were successfully synthesized using the polyacrylamide gel method for the first time.The results showed that phase composition,particle size,and agglomeration degree of the nanopowders were greatly influenced by the molar ratio of acrylamide(AM)/Zr and calcination temperature.These as-synthesized high-entropy zirconate(HEZ)nanopowders could be sintered into fully dense ceramics at 1500 C for 2 h.These HEZ nanopowders showed a phase transformation from a defect-fluorite phase to a pyrochlore phase with the increase of sintering temperature.Additionally,two-step sintering of these nanopowders was conducted,and the HEZ ceramics with fine grains were prepared.The polyacrylamide gel method is simple and easily operated,which is a facile approach of producing the HEC nanopowders with excellent sinterability.展开更多
Multicomponent rare earth phosphates hold immense potential as next-generation environmental barrier coatings(EBCs),offering enormous possibilities and flexibility by controlling and varying their components and fract...Multicomponent rare earth phosphates hold immense potential as next-generation environmental barrier coatings(EBCs),offering enormous possibilities and flexibility by controlling and varying their components and fractions to tailor their performance.In this work,the key material parameters(e.g.,ionic size and ionic size disorder)and the elements governing their thermal‒mechanical properties and resistance against calcium‒magnesium‒aluminosilicate(CMAS)corrosion were elucidated.The thermal conductivities of multicomponent rare-earth phosphates correlate well with cation size disorder,but no clear trend is identified for the coefficient of thermal expansion(CTE).Er-containing compositions display low CTEs and high fracture toughness.Rapid formation of a dense interfacial layer occurs for most CAMS corrosion-resistant compositions when tested at 1300°C,e.g.,(Lu_(0.2)Yb_(0.2)Er_(0.2)Y_(0.2)Gd_(0.2))PO_(4) and(Lu_(0.2)Yb_(0.2)Er_(0.2)Dy_(0.2)Gd_(0.2))PO_(4).These multicomponent phosphates also display the least recession upon molten CMAS attack at 1400°C without significant volumetric swelling,which is superior to their single-component counterparts and state-of-the-art EBCs based on rare-earth disilicates.In contrast,Sc-containing multicomponent phosphates display inferior performance against CMAS corrosion and penetration.A mechanistic understanding and understanding of the kinetics of the interfacial interaction at higher temperatures,as well as the key parameters governing their thermomechanical properties and CMAS corrosion,are valuable for designing data-driven materials of multicomponent phosphates for EBC applications.展开更多
In response to the development of the concepts of“carbon neutrality”and“carbon peak”,it is critical to developing materials with high near-infrared(NIR)solar reflectivity and high emissivity in the atmospheric tra...In response to the development of the concepts of“carbon neutrality”and“carbon peak”,it is critical to developing materials with high near-infrared(NIR)solar reflectivity and high emissivity in the atmospheric transparency window(ATW;8–13μm)to advance zero energy consumption radiative cooling technology.To regulate emission and reflection properties,a series of high-entropy rare earth stannate ceramics(HE-RE_(2)Sn_(2)O_(7):(Y_(0.2)La_(0.2)Nd_(0.2)Eu_(0.2)Gd_(0.2))_(2)Sn_(2)O_(7),(Y_(0.2)La_(0.2)Sm_(0.2)Eu_(0.2)Lu_(0.2))_(2)Sn_(2)O_(7),and(Y_(0.2)La_(0.2)Gd_(0.2)Yb_(0.2)Lu_(0.2))_(2)Sn_(2)O_(7))with severe lattice distortion were prepared using a solid phase reaction followed by a pressureless sintering method for the first time.Lattice distortion is accomplished by introducing rare earth elements with different cation radii and mass.The as-synthesized HE-RE_(2)Sn_(2)O_(7)ceramics possess high ATW emissivity(91.38%–95.41%),high NIR solar reflectivity(92.74%–97.62%),low thermal conductivity(1.080–1.619 W·m^(−1)·K^(−1)),and excellent chemical stability.On the one hand,the lattice distortion intensifies the asymmetry of the structural unit to cause a notable alteration in the electric dipole moment,ultimately enlarging the ATW emissivity.On the other hand,by selecting difficult excitation elements,HE-RE_(2)Sn_(2)O_(7),which has a wide band gap(Eg),exhibits high NIR solar reflectivity.Hence,the multi-component design can effectively enhance radiative cooling ability of HE-RE_(2)Sn_(2)O_(7)and provide a novel strategy for developing radiative cooling materials.展开更多
Two new high-entropy ceramics(HECs)in the weberite and fergusonite structures,along with the unexpected formation of ordered pyrochlore phases with ultrahigh-entropy compositions and an abrupt pyrochlore–weberite tra...Two new high-entropy ceramics(HECs)in the weberite and fergusonite structures,along with the unexpected formation of ordered pyrochlore phases with ultrahigh-entropy compositions and an abrupt pyrochlore–weberite transition,are discovered in a 21-component oxide system.While the Gibbs phase rule allows 21 equilibrium phases,9 out of the 13 compositions examined possess single HEC phases(with ultrahigh ideal configurational entropies:~2.7kB per cation or higher on one sublattice in most cases).Notably,(15RE_(1/15))(Nb_(1/2)Ta_(1/2))O_(4) possess a single monoclinic fergusonite(C2/c)phase,and(15RE_(1/15))_(3)(Nb_(1/2)Ta_(1/2))_(1)O_(7) form a single orthorhombic(C222_(1))weberite phase,where 15RE_(1/15) represents Sc_(1/15)Y_(1/15)La_(1/15)Pr_(1/15)Nd_(1/15)Sm_(1/15)Eu_(1/15)Gd_(1/15)Tb_(1/15)Dy_(1/15)Ho_(1/15)Er_(1/15)Tm_(1/15) Yb_(1/15)Lu_(1/15).Moreover,a series of eight(15RE_(1/15))_(2+x)(Ti_(1/4)Zr_(1/4)Ce_(1/4)Hf_(1/4))_(2−2x)(Nb_(1/2)Ta_(1/2))_(x)O_(7) specimens all exhibit single phases,where a pyrochlore–weberite transition occurs within 0.75<x<0.8125.This cubic-to-orthorhombic transition does not change the temperature-dependent thermal conductivity appreciably,as the amorphous limit may have already been achieved in the ultrahigh-entropy 21-component oxides.These discoveries expand the diversity and complexity of HECs,towards many-component compositionally complex ceramics(CCCs)and ultrahigh-entropy ceramics.展开更多
High-entropy alloys and ceramics containing at least five principal elements have recently received high attention for various mechanical and functional applications.The application of severe plastic deformation(SPD),...High-entropy alloys and ceramics containing at least five principal elements have recently received high attention for various mechanical and functional applications.The application of severe plastic deformation(SPD),particularly the high-pressure torsion method,combined with the CALPHAD(calculation of phase diagram) and first-principles calculations resulted in the development of numerous superfunctional high-entropy materials with superior properties compared to the normal functions of engineering materials.This article reviews the recent advances in the application of SPD to developing superfunctional high-entropy materials.These superfunctional properties include(ⅰ) ultrahigh hardness levels comparable to the hardness of ceramics in high-entropy alloys,(ⅱ) high yield strength and good hydrogen embrittlement resistance in high-entropy alloys;(ⅲ) high strength,low elastic modulus,and high biocompatibility in high-entropy alloys,(ⅳ) fast and reversible hydrogen storage in high-entropy hydrides,(ⅴ) photovoltaic performance and photocurrent generation on high-entropy semiconductors,(ⅵ) photocatalytic oxygen and hydrogen production from water splitting on high-entropy oxides and oxynitrides,and(ⅶ)CO_(2) photoreduction on high-entropy ceramics.These findings introduce SPD as not only a processing tool to improve the properties of existing high-entropy materials but also as a synthesis tool to produce novel high-entropy materials with superior properties compared with conventional engineering materials.展开更多
In recent years,high-entropy metal carbides(HECs)have attracted significant attention due to their exceptional physical and chemical properties.The combination of excellent performance exhibited by bulk HEC ceramics a...In recent years,high-entropy metal carbides(HECs)have attracted significant attention due to their exceptional physical and chemical properties.The combination of excellent performance exhibited by bulk HEC ceramics and distinctive geometric characteristics has paved the way for the emergence of one-dimensional(1D)HECs as novel materials with unique development potential.Herein,we successfully fabricated novel(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C nanowires derived via Fe-assisted single-sourced precursor pyrolysis.Prior to the synthesis of the nanowires,the composition and microstructure of(Ti,Zr,Hf,Nb,Ta)-containing precursor(PHECs)were analyzed,and divinylbenzene(DVB)was used to accelerate the conversion process of the precursor and contribute to the formation of HECs,which also provided a partial carbon source for the nanowire growth.Additionally,multi-branched,single-branched,and single-branched bending nanowires were synthesized by adjusting the ratio of PHECs to DVB.The obtained single-branched(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C nanowires possessed smooth surfaces with an average diameter of 130–150 nm and a length of several tens of micrometers,which were a single-crystal structure and typically grew along the[11¯1]direction.Also,the growth of the(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C nanowires was in agreement with top-type vapor–liquid–solid mechanism.This work not only successfully achieved the fabrication of HEC nanowires by a catalyst-assisted polymer pyrolysis,but also provided a comprehensive analysis of the factors affecting their yield and morphology,highlighting the potential application of these attractive nano-materials.展开更多
Environmental barrier coatings(EBCs)with excellent chemical resistance and good high-temperature stability are of great significance for their applications in next-generation turbine engines.In this work,a new type of...Environmental barrier coatings(EBCs)with excellent chemical resistance and good high-temperature stability are of great significance for their applications in next-generation turbine engines.In this work,a new type of high-entropy fluorite-structured oxide(Ce_(0.2)Hf_(0.2)Y_(0.2)Pr_(0.2)Gd_(0.2))O_(2−δ)(HEFO-1)with different Ti^(4+)contents were successfully synthesized.Minor addition of Ti4+could be dissolved into a high-entropy lattice to maintain the structure stable,effectively reducing the phase formation temperature and promoting the shrinkage of bulk samples.Heat treatment experiments showed that all the samples remained a single phase after annealing at 1200–1600℃for 6 h.In addition,high-entropy(Ce_(0.2)Hf_(0.2)Y_(0.2)Pr_(0.2)Gd_(0.2)Ti_(0.2x)O_(2−δ)demonstrated great resistance to calcium–magnesium–alumina–silicate(CMAS)thermochemical corrosion.When the content of Ti was increased to x=0.5,the average thickness of the reaction layer was about 10.5µm after being corroded at 1300℃for 10 h.This study reveals that high-entropy(Ce_(0.2)Hf_(0.2)Y_(0.2)Pr_(0.2)Gd_(0.2)Ti_(0.2x)O_(2−δ)is expected to be a candidate for the next-generation EBC materials with graceful resistance to CMAS corrosion.展开更多
The garnet-type electrolyte is one of the most promising solid-state electrolytes(SSEs)due to its high ionic conductivity(σ)and wide electrochemical window.However,such electrolyte generates lithium carbonate(Li_(2)C...The garnet-type electrolyte is one of the most promising solid-state electrolytes(SSEs)due to its high ionic conductivity(σ)and wide electrochemical window.However,such electrolyte generates lithium carbonate(Li_(2)CO_(3))in air,leading to an increase in impedance,which greatly limits their practical applications.In turn,high-entropy ceramics(HECs)can improve phase stability due to high-entropy effect.Herein,high-entropy garnet(HEG)Li_(6.2)La_(3)(Zr_(0.2)Hf_(0.2)Ti_(0.2)Nb_(0.2)Ta_(0.2))_(2)O_(12)(LL(ZrHfTiNbTa)O)SSEs were synthesized by the solid-state reaction method.X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),electrochemical impedance spectroscopy(EIS),and scanning electron microscopy(SEM)characterizations indicated that the LL(ZrHfTiNbTa)O electrolyte has excellent air stability.Room-temperature conductivity of LL(ZrHfTiNbTa)O can be maintained at~1.42×10^(-4)S/cm after exposure to air for 2 months.Single-element-doped garnets were synthesized to explain the role of different elements and the mechanism of air stabilization.In addition,a lithium(Li)/LL(ZrHfTiNbTa)O/Li symmetric cell cycle is stable over 600 h,and the critical current density(CCD)is 1.24 mA/cm^(2),indicating remarkable stability of the Li/LL(ZrHfTiNbTa)O interface.Moreover,the LiFePO_(4)/LL(ZrHfTiNbTa)O/Li cell shows excellent rate performance at 30℃.These results suggest that HECs can be one of the strategies for improving the performance of SSEs in the future due to their unique effects.展开更多
基金Financial supports from the National Natural Science Foundation of China under Grant Nos.51972089,51672064,and U1435206 are also acknowledged.
文摘High-entropy ceramics (HECs) are solid solutions of inorganic compounds with one or more Wyckoff sites shared by equal or near-equal atomic ratios of multi-principal elements.Although in the infant stage,the emerging of this new family of materials has brought new opportunities for material design and property tailoring.Distinct from metals,the diversity in crystal structure and electronic structure of ceramics provides huge space for properties tuning through band structure engineering and phonon engineering.Aside from strengthening,hardening,and low thermal conductivity that have already been found in high-entropy alloys,new properties like colossal dielectric constant,super ionic conductivity,severe anisotropic thermal expansion coefficient,strong electromagnetic wave absorption,etc.,have been discovered in HECs.As a response to the rapid development in this nascent field,this article gives a comprehensive review on the structure features,theoretical methods for stability and property prediction,processing routes,novel properties,and prospective applications of HECs.The challenges on processing,characterization,and property predictions are also emphasized.Finally,future directions for new material exploration,novel processing,fundamental understanding,in-depth characterization,and database assessments are given.
基金financial support from the National Natural Science Foundation of China(Grant Nos.51672064 and 51972089).
文摘The critical requirements for the environmental barrier coating(EBC)materials of silicon-based ceramic matrix composites(CMCs)include good tolerance to harsh environments,thermal expansion matches with the interlayer mullite,good high-temperature phase stability,and low thermal conductivity.Cuspidine-structured rare-earth aluminates RE_(4)Al_(2)O_(9) have been considered as candidates of EBCs for their superior mechanical and thermal properties,but the phase transition at high temperatures is a notable drawback of these materials.To suppress the phase transition and improve the phase stability,a novel cuspidine-structured rare-earth aluminate solid solution(Nd_(0.2)Sm_(0.2)Eu_(0.2)Y_(0.2)Yb_(0.2))_(4)Al_(2)O_(9) was designed and successfully synthesized inspired by entropy stabilization effect of high-entropy ceramics(HECs).The as-synthesized HE(Nd_(0.2)Sm_(0.2)Eu_(0.2)Y_(0.2)Yb_(0.2))_(4)Al_(2)O_(9) exhibits a close thermal expansion coefficient(6.96×10^(-6) K^(-1) at 300-1473 K)to that of mullite,good phase stability from 300 to 1473 K,and low thermal conductivity(1.50 W·m^(-1)·K^(-1) at room temperature).In addition,strong anisotropic thermal expansion has been observed compared to Y_(4)Al_(2)O_(9) and Yb_(4)Al_(2)O_(9).The mechanism for low thermal conductivity is attributed to the lattice distortion and mass difference of the constituent atoms,and the anisotropic thermal expansion is due to the anisotropic chemical bonding enhanced by the large size rare-earth cations.
文摘Four high-entropy perovskite(HEP)RETa_(3)O_(9) samples were fabricated via a spark plasma sintering(SPS)method,and the corresponding thermophysical properties and underlying mechanisms were investigated for environmental/thermal barrier coating(E/TBC)applications.The prepared samples maintained low thermal conductivity(1.50 W·m^(−1)·K^(−1)),high hardness(10 GPa),and an appropriate Young’s modulus(180 GPa),while the fracture toughness increased to 2.5 MPa·m^(1/2).Nanoindentation results showed the HEP ceramics had excellent mechanical properties and good component homogeneity.We analysed the influence of different parameters(the disorder parameters of the electronegativity,ionic radius,and atomic mass,as well as the tolerance factor)of A-site atoms on the thermal conductivity.Enhanced thermal expansion coefficients,combined with a high melting point and extraordinary phase stability,expanded the applications of the HEP RETa_(3)O_(9).The results of this study had motivated a follow-up study on tantalate high-entropy ceramics with desirable properties.
基金the National Key Research and Development Program of China(2017YFB0701600)the National Natural Science Foundation of China(11874254,51622207,and U1630134)。
文摘Rational design of solid-state electrolytes(SSEs)with high ionic conductivity and low activation energy(Ea)is vital for all solid-state batteries.Machine learning(ML)techniques have recently been successful in predicting Li^(+) conduction property in SSEs with various descriptors and accelerating the development of SSEs.In this work,we extend the previous efforts and introduce a framework of ML prediction for E_(a) in SSEs with hierarchically encoding crystal structure-based(HECS)descriptors.Taking cubic Li-argyrodites as an example,an Ea prediction model is developed to the coefficient of determination(R^(2))and rootmean-square error(RMSE)values of 0.887 and 0.02 eV for training dataset,and 0.820 and 0.02 eV for test dataset,respectively by partial least squares(PLS)analysis,proving the prediction power of HECSdescriptors.The variable importance in projection(VIP)scores demonstrate the combined effects of the global and local Li^(+) conduction environments,especially the anion size and the resultant structural changes associated with anion site disorder.The developed E_(a) prediction model directs us to optimize and design new Li-argyrodites with lower Ea,such as Li_(6–x)PS_(5–x)Cl_(1+x)(<0.322 eV),Li_(6+x)PS_(5+x)Br_(1–x)(<0.273 eV),Li_(6+x)PS_(5+x)Br_(0.25)I_(0.75–x)(<0.352 eV),Li_(6+(5–n)y)P_(1–y)N_(y)S_(5)I(<0.420 eV),Li_(6+(5–n)y)As_(1–y)N_(y)S_(5)I(<0.371 eV),Li_(6+(5–n)y)As_(1–y)NySe_(5)I(<0.450 eV),by broadening bottleneck size,invoking site disorder and activating concerted Li+conduction.This analysis shows great potential in promoting rational design of advanced SSEs and the same approach can be applied to other types of materials.
基金supported by the National Natural Science Foundation of China(Grant Nos.51802289 and 51972089)Financial supports of the Science Foundation for the Excellent Youth Scholars of Henan Province(Grant No.212300410089)the Support Program for Scientific and Technological Innovation Talents of Higher Education in Henan Province(Grant No.21HASTIT004)。
文摘Ferrites are the most widely used microwave absorbing materials to deal with the threat of electromagnetic(EM)pollution.However,the lack of sufficient dielectric loss capacity is the main challenge that limits their applications.To cope with this challenge,three high-entropy(HE)spineltype ferrite ceramics including(Mg_(0.2)Mn_(0.2)Fe_(0.2)Co_(0.2)Ni_(0.2))Fe_(2)O_(4),(Mg_(0.2)Fe_(0.2)Co_(0.2)Ni_(0.2)Cu_(0.2))Fe_(2)O_(4),and(Mg_(0.2)Fe_(0.2)Co_(0.2)Ni_(0.2)Zn_(0.2))Fe_(2)O_(4)were designed and successfully prepared through solid state synthesis.The results show that all three HE MFe_(2)O_(4) samples exhibit synergetic dielectric loss and magnetic loss.The good magnetic loss ability is due to the presence of magnetic components;while the enhanced dielectric properties are attributed to nano-domain,hopping mechanism of resonance effect and HE effect.Among three HE spinels,(Mg_(0.2)Mn_(0.2)Fe_(0.2)Co_(0.2)Ni_(0.2))Fe_(2)O_(4)shows the best EM wave absorption performance,e.g.,its minimum reflection loss(RL_(min))reaches-35.10 dB at 6.78 GHz with a thickness of 3.5 mm,and the optimized effective absorption bandwidth(EAB)is 7.48 GHz from 8.48 to 15.96 GHz at the thickness of 2.4 mm.Due to the easy preparation and strong EM dissipation ability,HE MFe_(2)O_(4) are promising as a new type of EM absorption materials.
基金supported by the National Key R&D Program of China(No.2021YFB3701404)the National Science Fund for Distinguished Young Scholars(No.52025041)the National Natural Science Foundation of China(Nos.51904021 and 52174294).
文摘Rare-earth phosphates(REPO4)are regarded as one of the promising thermal/environmental barrier coating(T/EBC)materials for SiCf/SiC ceramic matrix composites(SiC-CMCs)owing to their excellent resistance to water vapor and CaO–MgO–Al_(2)O_(3)–SiO_(2)(CMAS).Nevertheless,a relatively high thermal conductivity(κ)of the REPO_(4) becomes the bottleneck for their practical applications.In this work,novel xenotime-type high-entropy(Dy_(1/7)Ho_(1/7)Er_(1/7)Tm_(1/7)Yb_(1/7)Lu_(1/7)Y_(1/7))PO4(HE(7RE_(1/7))PO_(4))has been designed and synthesized for the first time to solve this issue.HE(7RE_(1/7))PO_(4) with a homogeneous rare-earth element distribution exhibits high thermal stability up to 1750℃and good chemical compatibility with SiO_(2) up to 1400℃.In addition,the thermal expansion coefficient(TEC)of HE(7RE_(1/7))PO_(4)(5.96×10^(−6)℃^(−1) from room temperature(RT)to 900℃)is close to that of the SiC-CMCs.What is more,the thermal conductivities of HE(7RE_(1/7))PO_(4)(from 4.38 W·m^(−1)·K^(−1) at 100℃to 2.25 W·m^(−1)·K^(−1) at 1300℃)are significantly decreased compared to those of single-component REPO4 with the minimum value ranging from 9.90 to 4.76 W·m^(−1)·K^(−1).These results suggest that HE(7RE_(1/7))PO_(4) has the potential to be applied as the T/EBC materials for the SiC-CMCs in the future.
基金supported by the Key Research and Development Projects of Shaanxi Province(Grant No.2021GY-250)the Open Project of State Key Laboratory of Environment-Friendly Energy Materials(Grant No.20kfhg06)the Fundamental Research Funds for the Central Universities of China(Grant No.300102312406).
文摘The challenge in synthesizing high-entropy ceramic(HEC)nanopowders is to suppress severe grain coarsening and particle agglomeration,which occur at elevated temperatures.This challenge could be addressed by the polyacrylamide gel method.In this work,single-phase high-entropy(Lao.2Ndo.2Smo.2Gdo.2 Ybo.2)2Zr2O7 and(Lao.2Ndo.2Yo.2Euo.2Gdo.2)2Zr2O7 nanopowders without agglomeration were successfully synthesized using the polyacrylamide gel method for the first time.The results showed that phase composition,particle size,and agglomeration degree of the nanopowders were greatly influenced by the molar ratio of acrylamide(AM)/Zr and calcination temperature.These as-synthesized high-entropy zirconate(HEZ)nanopowders could be sintered into fully dense ceramics at 1500 C for 2 h.These HEZ nanopowders showed a phase transformation from a defect-fluorite phase to a pyrochlore phase with the increase of sintering temperature.Additionally,two-step sintering of these nanopowders was conducted,and the HEZ ceramics with fine grains were prepared.The polyacrylamide gel method is simple and easily operated,which is a facile approach of producing the HEC nanopowders with excellent sinterability.
基金supported as part of the DMREF:Machine Learning Accelerated Design and Discovery of Rare-earth Phosphates as Next-Generation Environmental Barrier Coatings,a standard grant funded by the Division of Materials Research,National Science Foundation under Award DMREF-2119423.
文摘Multicomponent rare earth phosphates hold immense potential as next-generation environmental barrier coatings(EBCs),offering enormous possibilities and flexibility by controlling and varying their components and fractions to tailor their performance.In this work,the key material parameters(e.g.,ionic size and ionic size disorder)and the elements governing their thermal‒mechanical properties and resistance against calcium‒magnesium‒aluminosilicate(CMAS)corrosion were elucidated.The thermal conductivities of multicomponent rare-earth phosphates correlate well with cation size disorder,but no clear trend is identified for the coefficient of thermal expansion(CTE).Er-containing compositions display low CTEs and high fracture toughness.Rapid formation of a dense interfacial layer occurs for most CAMS corrosion-resistant compositions when tested at 1300°C,e.g.,(Lu_(0.2)Yb_(0.2)Er_(0.2)Y_(0.2)Gd_(0.2))PO_(4) and(Lu_(0.2)Yb_(0.2)Er_(0.2)Dy_(0.2)Gd_(0.2))PO_(4).These multicomponent phosphates also display the least recession upon molten CMAS attack at 1400°C without significant volumetric swelling,which is superior to their single-component counterparts and state-of-the-art EBCs based on rare-earth disilicates.In contrast,Sc-containing multicomponent phosphates display inferior performance against CMAS corrosion and penetration.A mechanistic understanding and understanding of the kinetics of the interfacial interaction at higher temperatures,as well as the key parameters governing their thermomechanical properties and CMAS corrosion,are valuable for designing data-driven materials of multicomponent phosphates for EBC applications.
基金the Lingchuang Research Project of China National Nuclear Co.,the National Key R&D Program of China(No.2022YFB3504302)the Fujian Provincial Natural Fund Project(No.2021J05101)+1 种基金the Young Elite Scientists Sponsorship Program by CAST(No.YESS20210336)the XMIREM autonomously deployment project(No.2023GG03).
文摘In response to the development of the concepts of“carbon neutrality”and“carbon peak”,it is critical to developing materials with high near-infrared(NIR)solar reflectivity and high emissivity in the atmospheric transparency window(ATW;8–13μm)to advance zero energy consumption radiative cooling technology.To regulate emission and reflection properties,a series of high-entropy rare earth stannate ceramics(HE-RE_(2)Sn_(2)O_(7):(Y_(0.2)La_(0.2)Nd_(0.2)Eu_(0.2)Gd_(0.2))_(2)Sn_(2)O_(7),(Y_(0.2)La_(0.2)Sm_(0.2)Eu_(0.2)Lu_(0.2))_(2)Sn_(2)O_(7),and(Y_(0.2)La_(0.2)Gd_(0.2)Yb_(0.2)Lu_(0.2))_(2)Sn_(2)O_(7))with severe lattice distortion were prepared using a solid phase reaction followed by a pressureless sintering method for the first time.Lattice distortion is accomplished by introducing rare earth elements with different cation radii and mass.The as-synthesized HE-RE_(2)Sn_(2)O_(7)ceramics possess high ATW emissivity(91.38%–95.41%),high NIR solar reflectivity(92.74%–97.62%),low thermal conductivity(1.080–1.619 W·m^(−1)·K^(−1)),and excellent chemical stability.On the one hand,the lattice distortion intensifies the asymmetry of the structural unit to cause a notable alteration in the electric dipole moment,ultimately enlarging the ATW emissivity.On the other hand,by selecting difficult excitation elements,HE-RE_(2)Sn_(2)O_(7),which has a wide band gap(Eg),exhibits high NIR solar reflectivity.Hence,the multi-component design can effectively enhance radiative cooling ability of HE-RE_(2)Sn_(2)O_(7)and provide a novel strategy for developing radiative cooling materials.
基金The work is supported by the National Science Foundation(NSF)in the Ceramics program via Grant No.DMR2026193This work utilized the shared facilities at the San Diego Nanotechnology Infrastructure of UCSD,a member of the National Nanotechnology Coordinated Infrastructure(supported by the NSF ECCS-1542148)the Irvine Materials Research Institute(partially supported by NSF DMR-2011967 through UCI CCAM).
文摘Two new high-entropy ceramics(HECs)in the weberite and fergusonite structures,along with the unexpected formation of ordered pyrochlore phases with ultrahigh-entropy compositions and an abrupt pyrochlore–weberite transition,are discovered in a 21-component oxide system.While the Gibbs phase rule allows 21 equilibrium phases,9 out of the 13 compositions examined possess single HEC phases(with ultrahigh ideal configurational entropies:~2.7kB per cation or higher on one sublattice in most cases).Notably,(15RE_(1/15))(Nb_(1/2)Ta_(1/2))O_(4) possess a single monoclinic fergusonite(C2/c)phase,and(15RE_(1/15))_(3)(Nb_(1/2)Ta_(1/2))_(1)O_(7) form a single orthorhombic(C222_(1))weberite phase,where 15RE_(1/15) represents Sc_(1/15)Y_(1/15)La_(1/15)Pr_(1/15)Nd_(1/15)Sm_(1/15)Eu_(1/15)Gd_(1/15)Tb_(1/15)Dy_(1/15)Ho_(1/15)Er_(1/15)Tm_(1/15) Yb_(1/15)Lu_(1/15).Moreover,a series of eight(15RE_(1/15))_(2+x)(Ti_(1/4)Zr_(1/4)Ce_(1/4)Hf_(1/4))_(2−2x)(Nb_(1/2)Ta_(1/2))_(x)O_(7) specimens all exhibit single phases,where a pyrochlore–weberite transition occurs within 0.75<x<0.8125.This cubic-to-orthorhombic transition does not change the temperature-dependent thermal conductivity appreciably,as the amorphous limit may have already been achieved in the ultrahigh-entropy 21-component oxides.These discoveries expand the diversity and complexity of HECs,towards many-component compositionally complex ceramics(CCCs)and ultrahigh-entropy ceramics.
基金the Hosokawa Powder Technology Foundation of Japan for a grantsupported by the MEXT, Japan through Grants-in-Aid for Scientific Research on Innovative Areas (Nos. JP19H05176 and JP21H00150)in part by the MEXT, Japan through Grant-in-Aid for Challenging Research Exploratory (No. JP22K18737)。
文摘High-entropy alloys and ceramics containing at least five principal elements have recently received high attention for various mechanical and functional applications.The application of severe plastic deformation(SPD),particularly the high-pressure torsion method,combined with the CALPHAD(calculation of phase diagram) and first-principles calculations resulted in the development of numerous superfunctional high-entropy materials with superior properties compared to the normal functions of engineering materials.This article reviews the recent advances in the application of SPD to developing superfunctional high-entropy materials.These superfunctional properties include(ⅰ) ultrahigh hardness levels comparable to the hardness of ceramics in high-entropy alloys,(ⅱ) high yield strength and good hydrogen embrittlement resistance in high-entropy alloys;(ⅲ) high strength,low elastic modulus,and high biocompatibility in high-entropy alloys,(ⅳ) fast and reversible hydrogen storage in high-entropy hydrides,(ⅴ) photovoltaic performance and photocurrent generation on high-entropy semiconductors,(ⅵ) photocatalytic oxygen and hydrogen production from water splitting on high-entropy oxides and oxynitrides,and(ⅶ)CO_(2) photoreduction on high-entropy ceramics.These findings introduce SPD as not only a processing tool to improve the properties of existing high-entropy materials but also as a synthesis tool to produce novel high-entropy materials with superior properties compared with conventional engineering 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)ND Basic Research Funds of Northwestern Polytechnical University(Grant No.G2022WD).
文摘In recent years,high-entropy metal carbides(HECs)have attracted significant attention due to their exceptional physical and chemical properties.The combination of excellent performance exhibited by bulk HEC ceramics and distinctive geometric characteristics has paved the way for the emergence of one-dimensional(1D)HECs as novel materials with unique development potential.Herein,we successfully fabricated novel(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C nanowires derived via Fe-assisted single-sourced precursor pyrolysis.Prior to the synthesis of the nanowires,the composition and microstructure of(Ti,Zr,Hf,Nb,Ta)-containing precursor(PHECs)were analyzed,and divinylbenzene(DVB)was used to accelerate the conversion process of the precursor and contribute to the formation of HECs,which also provided a partial carbon source for the nanowire growth.Additionally,multi-branched,single-branched,and single-branched bending nanowires were synthesized by adjusting the ratio of PHECs to DVB.The obtained single-branched(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C nanowires possessed smooth surfaces with an average diameter of 130–150 nm and a length of several tens of micrometers,which were a single-crystal structure and typically grew along the[11¯1]direction.Also,the growth of the(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C nanowires was in agreement with top-type vapor–liquid–solid mechanism.This work not only successfully achieved the fabrication of HEC nanowires by a catalyst-assisted polymer pyrolysis,but also provided a comprehensive analysis of the factors affecting their yield and morphology,highlighting the potential application of these attractive nano-materials.
基金supported by the National Natural Science Foundation for Young Scientists of China(Grant No.51802213)Program of Applied Basic Research Program of Shanxi Province(Grant No.201901D211118)Key R&D Program of Shanxi Province(Grant No.202102030201006).
文摘Environmental barrier coatings(EBCs)with excellent chemical resistance and good high-temperature stability are of great significance for their applications in next-generation turbine engines.In this work,a new type of high-entropy fluorite-structured oxide(Ce_(0.2)Hf_(0.2)Y_(0.2)Pr_(0.2)Gd_(0.2))O_(2−δ)(HEFO-1)with different Ti^(4+)contents were successfully synthesized.Minor addition of Ti4+could be dissolved into a high-entropy lattice to maintain the structure stable,effectively reducing the phase formation temperature and promoting the shrinkage of bulk samples.Heat treatment experiments showed that all the samples remained a single phase after annealing at 1200–1600℃for 6 h.In addition,high-entropy(Ce_(0.2)Hf_(0.2)Y_(0.2)Pr_(0.2)Gd_(0.2)Ti_(0.2x)O_(2−δ)demonstrated great resistance to calcium–magnesium–alumina–silicate(CMAS)thermochemical corrosion.When the content of Ti was increased to x=0.5,the average thickness of the reaction layer was about 10.5µm after being corroded at 1300℃for 10 h.This study reveals that high-entropy(Ce_(0.2)Hf_(0.2)Y_(0.2)Pr_(0.2)Gd_(0.2)Ti_(0.2x)O_(2−δ)is expected to be a candidate for the next-generation EBC materials with graceful resistance to CMAS corrosion.
基金funded by the Central Government Guides Local Science and Technology Development Special Fund Projects(Grant No.YDZJSX2022B003)the Shanxi Province Science and Technology Major Projects(Grant No.202101120401008)+1 种基金the Key Research and Development Project of Shanxi Province(Grant No.202102030201006)Science and Technology Activities of Overseas Students Merit-based Funding Projects of Shanxi Province(Grant No.2021037).
文摘The garnet-type electrolyte is one of the most promising solid-state electrolytes(SSEs)due to its high ionic conductivity(σ)and wide electrochemical window.However,such electrolyte generates lithium carbonate(Li_(2)CO_(3))in air,leading to an increase in impedance,which greatly limits their practical applications.In turn,high-entropy ceramics(HECs)can improve phase stability due to high-entropy effect.Herein,high-entropy garnet(HEG)Li_(6.2)La_(3)(Zr_(0.2)Hf_(0.2)Ti_(0.2)Nb_(0.2)Ta_(0.2))_(2)O_(12)(LL(ZrHfTiNbTa)O)SSEs were synthesized by the solid-state reaction method.X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),electrochemical impedance spectroscopy(EIS),and scanning electron microscopy(SEM)characterizations indicated that the LL(ZrHfTiNbTa)O electrolyte has excellent air stability.Room-temperature conductivity of LL(ZrHfTiNbTa)O can be maintained at~1.42×10^(-4)S/cm after exposure to air for 2 months.Single-element-doped garnets were synthesized to explain the role of different elements and the mechanism of air stabilization.In addition,a lithium(Li)/LL(ZrHfTiNbTa)O/Li symmetric cell cycle is stable over 600 h,and the critical current density(CCD)is 1.24 mA/cm^(2),indicating remarkable stability of the Li/LL(ZrHfTiNbTa)O interface.Moreover,the LiFePO_(4)/LL(ZrHfTiNbTa)O/Li cell shows excellent rate performance at 30℃.These results suggest that HECs can be one of the strategies for improving the performance of SSEs in the future due to their unique effects.
