Near-infrared phosphor-converted light-emitting diodes(NIR pc-LEDs),one of the most promising NIR light sources,have garnered significant attention owing to their compact structure,long lifetime and energy conservatio...Near-infrared phosphor-converted light-emitting diodes(NIR pc-LEDs),one of the most promising NIR light sources,have garnered significant attention owing to their compact structure,long lifetime and energy conservation.Despite these advantages,commercial NIR pc-LEDs employing pseudotransmission configurations,where the NIR phosphor and silicone composites are directly coated on blue LED chips,suffer from critical limitations in thermal management that severely deteriorate their NIR output performance.To address these intrinsic limitations,we developed an oxygen-coordination-competitive crystallization strategy to engineer high-transparencyβ-Ga_(2)O_(3):Cr^(3+)glass-ceramics(GC).This strategy leveraged the strong oxygen affinity of Ga^(3+)ions,which drove the directional migration and recombination of Ga^(3+)and O^(2-)ions within the isolated[GaO_(4)]tetrahedral network during thermal processing.This controlled phase evolution enabled localized crystallization of theβ-Ga_(2)O_(3):Cr^(3+)nanocrystals while maintaining high transparency.The optimizedβ-Ga_(2)O_(3):Cr^(3+)GC(0.4 mm thickness)achieved remarkable 81.2%NIR transmittance,approaching internal quantum efficiency(IQE≈100%)and high thermal stability(89%@423 K).When this hightransparencyβ-Ga_(2)O_(3):Cr^(3+)GC was employed as the NIR conversion material,the NIR GC-converted LEDs(GCc-LEDs)achieved 568 mW of NIR output power at a 500 mA drive current with a photoelectric conversion efficiency of 13%.The demonstrated performance metrics of NIR GCc-LEDs positioned this technology as an ideal NIR illumination source for next-generation point-of-care diagnostics,intelligent night vision systems,and nondestructive testing applications.展开更多
To improve the high-temperature ablation resistance properties of Ta(W) refractory alloys, a novel ultra-high-temperature ceramic (UHTC) composite coating was prepared by combining the technological advantages of high...To improve the high-temperature ablation resistance properties of Ta(W) refractory alloys, a novel ultra-high-temperature ceramic (UHTC) composite coating was prepared by combining the technological advantages of high-speed laser cladding (HSLC) and pack cementation (PC). First, the HSLC process was employed to fabricate a (Hf,Ta)C–Ta(W) UHTC–refractory metal composite coating that had metallurgical bonding with the Ta(W) substrate. Then, the PC process was utilized to transform the refractory metal phase in the coating into the corresponding refractory silicide (RMSi_(2)) phase. Consequently, the (Hf,Ta)C–TaSi_(2) UHTC composite coating was successfully prepared. This new coating was ablated at a heat flux density of 8.0 MW/m^(2) for 300 s at a surface temperature of 2300 ℃, and the structural integrity of the coating was retained. The linear ablation rate of the coating is −0.67 µm/s. The ablated coating exhibits three distinct oxide layers: a loose HfO_(2) top layer, a dense HfO_(2) middle layer, and a slightly oxidized (Hf,Ta)CxOy–Hf–Ta–O glassy layer. The synergistic effect of HfO_(2) and Hf–Ta–O glassy oxide film endows the coating with excellent anti-ablation resistance. This innovative design of the UHTC–RMSi_(2) composite coating provides robust protection to the Ta(W) substrate from ultra-high temperature ablation and mechanical scouring.展开更多
Porous ceramics are lightweight materials with diverse pore structures and are widely applied in areas such as thermal insulation, sound absorption, filtration, catalysis, and energy storage. However, excessive shrink...Porous ceramics are lightweight materials with diverse pore structures and are widely applied in areas such as thermal insulation, sound absorption, filtration, catalysis, and energy storage. However, excessive shrinkage during the sintering process of porous ceramics leads to cracking and deterioration, posing significant challenges for achieving complex shapes. Despite its importance, the field of low sintering shrinkage porous ceramics has not received sufficient attention. This review systematically discusses the principles and progress in the development of low sintering shrinkage porous ceramics. First, we introduce the characteristics of various preparation methods, including partial sintering, particle-stabilized foaming, gel-casting, foam-gelcasting, and additive manufacturing (AM). We then explain three primary principles of low sintering shrinkage from the perspectives of the volume effect and mass transfer processes. This review focuses on the properties and applications of typical low sintering shrinkage ceramics such as mullite and alumina, particularly their mechanical properties and thermal conductivity as thermal insulation and ceramic cores. Finally, we summarize the current state and present future perspectives on low sintering shrinkage porous ceramics.展开更多
A high voltage gradient(V_(g))of ZnO-based varistor ceramics is critical for realizing miniaturized and lightweight overvoltage protection devices.However,improving V_(g) of ZnObased varistor ceramics through conventi...A high voltage gradient(V_(g))of ZnO-based varistor ceramics is critical for realizing miniaturized and lightweight overvoltage protection devices.However,improving V_(g) of ZnObased varistor ceramics through conventional high-temperature sintering process remains a significant challenge.Here,we present a strategy to fabricate ultrahigh voltage-gradient ZnO-based varistor ceramics by combining cold sintering process/spark plasma sintering(CSP–SPS)with post-annealing process.Employing CSP–SPS,the ZnO-based varistor ceramics were initially densified at 300℃ and subsequently annealed at a low temperature of 700–900℃.CSP–SPS technique combined with a low annealing temperature enables the production of ZnO-based varistor ceramics with fine and homogeneous microstructures,while suppressing the volatilization of Bi-rich phases at grain boundaries.This approach achieves the ultrahigh V_(g) of~1832.71 V/mm,high nonlinear coefficient(α)of~106.69,and low leakage current density(J_(L))of less than 0.2μA/cm^(2).This work shows that the integration of CSP–SPS and post-annealing provides a promising way to design ZnO-based varistor ceramics with ultrahigh V_(g).展开更多
The reactive air brazing(RAB)process of ceramics was developed in the early 2000s because high-temperature electrochemical devices,such as solid oxide fuel cells(SOFCs),gas separators,reformers,and ion transport membr...The reactive air brazing(RAB)process of ceramics was developed in the early 2000s because high-temperature electrochemical devices,such as solid oxide fuel cells(SOFCs),gas separators,reformers,and ion transport membrane systems,are increasingly emerging.Accordingly,the reactive air wetting(RAW)and RAB of oxide ceramics have been investigated.Starting from the introduction of the advantages of the RAB process,the thermal expansion coefficients(TECs)of related materials,and the estimation of the TECs of Ag-based composite fillers,the RAW and RAB of ceramics are reviewed by classifying the employed ceramic materials,which mainly include yttria-stabilized zirconia(YSZ),perovskite oxides,Al_(2)O_(3),and nonoxide ceramics.In particular,the RAW and RAB processes,interfacial microstructures,reaction products,and joint reliability(including joint strength,fracture energy,gas tightness,and high-temperature aging resistance)are highlighted for understanding interfacial behavior and joint performance and developing application-oriented brazing technology.Finally,some helpful conclusions are drawn after summarizing the RAB of oxide ceramics.The prospects for RAB of SiC and high-entropy oxide ceramics are proposed after summarizing the RAB of oxide and nonoxide ceramics,and several aspects are proposed for promoting the development and application of RAB technology.展开更多
High operating temperatures generally degrade the luminous performance of color converters used in high-power,laser-driven white lighting systems.This study demonstrated that the operating temperature of LuAG:Ce films...High operating temperatures generally degrade the luminous performance of color converters used in high-power,laser-driven white lighting systems.This study demonstrated that the operating temperature of LuAG:Ce films can be significantly reduced,particularly under high-power laser excitation near the saturation threshold.This improvement was achieved by enhancing the crystallinity and increasing the Ce^(3+)content in LuAG:Ce films.LuAG:Ce films,approximately 22.17μm in thickness,were deposited on sapphire substrates via spray pyrolysis techniques.The crystallinity was controlled by the annealing temperature,while the Ce^(3+)content was regulated by the annealing atmosphere.Compared with those with a crystallinity of 75.5%,the air-annealed films with a crystallinity of 87.4%exhibited a remarkable 95.6℃decrease in operating temperature under 18 W/mm^(2)blue laser excitation.Additionally,the incorporation of a higher Ce^(3+)content through CO annealing led to a further reduction in the operating temperature.By lowering the operating temperature,LuAG:Ce films on sapphire substrates exhibit enhanced luminous performance and thermal stability under prolonged high-power laser excitation,which could inspire the design and development of advanced color converters for laser lighting applications.展开更多
The development of aeroengine with a high thrust-weight ratio poses great challenges for current top-coating thermal barrier coatings (TBCs) and environmental barrier coatings (EBCs) in service. Medium/high-entropy ce...The development of aeroengine with a high thrust-weight ratio poses great challenges for current top-coating thermal barrier coatings (TBCs) and environmental barrier coatings (EBCs) in service. Medium/high-entropy ceramics are highly promising candidate material for advanced TBCs/EBCs owing to their low thermal conductivity, high melting point, high-temperature stability, and calcium–magnesium–alumino–silicate (CMAS) resistance. Most feedstock powder used for medium/high-entropy TBCs/EBCs is prepared via traditional spray drying, which cannot fully exploit the advantages of multicomponent ceramics. The density, sphericity, inner structure, and flowability of feedstock powder affect their melting state during the thermal spraying process, which strongly affects the microstructure and properties of the deposited coatings. Therefore, the deposited coatings exhibit phase segregation, amorphous phases, and microstructure defects owing to unpredictable variations in feedstock powder with random morphologies and structures. Here, the structure and properties of feedstock powder prepared by state-of-the-art granulation technologies and their influences on the deposited coatings were systematically investigated, which can provide guidance for configuration optimization of feedstock powder and the manufacturing accuracy of the deposited coating. This review aims to bridge the gap between cutting-edge ceramics and advanced engineering technologies, thus providing concrete background knowledge and crucial guidelines for designing and developing TBCs/EBCs.展开更多
Defect engineering enables the efficient management of electromagnetic parameters and the enhancement of electromagnetic wave(EMW)absorption.In this study,(Fe_(1−x)Mn_(x))_(2)AlB_(2) transition metal boride(MAB)phases...Defect engineering enables the efficient management of electromagnetic parameters and the enhancement of electromagnetic wave(EMW)absorption.In this study,(Fe_(1−x)Mn_(x))_(2)AlB_(2) transition metal boride(MAB)phases with a layered structure were prepared via Joule heating-driven ultrafast synthesis,and their EMW absorption properties were investigated.The experimental results demonstrate that the incorporation of Mn atoms at the M site can effectively modulate the impedance matching and EMW absorption properties of the material through the introduction of defects and lattice distortions.Notably,(Fe_(0.3)Mn_(0.7))_(2)AlB_(2) exhibits a reflection loss as high as−47.8 dB at 12.24 GHz,with a maximum effective absorption bandwidth of 4.16 GHz(10.24-14.40 GHz)at an ultrasmall thickness of 1.5 mm.This study provides a promising avenue for the development of excellent microwave-absorbing materials,which are essential for meeting the evolving requirements of advanced electronics.Additionally,this work offers a paradigm for enhancing other properties of MAB phases through defect engineering.展开更多
Wireless surface acoustic wave(SAW)sensors hold great promise for in-situ,real-time monitoring and accurately assessing the health status of hot-end components.However,the thin-film electrode as the SAW sensor core un...Wireless surface acoustic wave(SAW)sensors hold great promise for in-situ,real-time monitoring and accurately assessing the health status of hot-end components.However,the thin-film electrode as the SAW sensor core unit with excellent high-temperature conductivity,stability,and oxidation resistance is still a challenge,especially in harsh ultra-high-temperature environments.In this study,we employed a polymer-derived ceramic approach to fabricate smooth and dense SiHfBCN ceramic coatings on YCa_(4)O(BO_(3))_(3)/BN substrate.The composition,microstructural evolution,and room-temperature and high-temperature electrical conductivity of SiHfBCN ceramic coatings were investigated to reveal the mechanism for controlling electrical conductivity.The results indicate that the electrical conductivity of the SiHfBCN ceramic coating pyrolyzed at a lower temperature of 1200℃reaches an impressive high value of 291.55 S·m^(-1) at 1200℃in argon.Importantly,the results also demonstrate that the coating has remarkable high-temperature conductivity and excellent repeatability and durability.Therefore,the typical semiconducting behavior of SiHfBCN ceramic coatings highlights their potential as thin-film electrodes for SAW high-temperature sensors in high-temperature extreme environments.展开更多
To obtain high-entropy carbide(HEC)joints with excellent high-temperature performance,a(HfZrTiTaNb)C HEC joint featuring a direct diffusion-bonded interface with a Nb-based interlayer was successfully fabricated at re...To obtain high-entropy carbide(HEC)joints with excellent high-temperature performance,a(HfZrTiTaNb)C HEC joint featuring a direct diffusion-bonded interface with a Nb-based interlayer was successfully fabricated at relatively low temperatures of 1150–1250℃for 60 min under 10 MPa.Starting from a modified Ni/Nb/Ni composite interlayer with a Nb content of>64 at%,an alloyed Nb_(2)Ni layer was constructed in situ by accelerating the directional diffusion of Ni atoms from the high-entropy interface into the remaining pure Nb through the Ni‒Nb eutectic liquid.Moreover,the excess liquid phase was squeezed out of the bonding region,ensuring the absence of Ni-based compounds.Leveraging the intrinsic interfacial stability and sluggish diffusion effect,the HEC with its original lattice structure,was capable of developing diffusion bonding with the Nb_(2)Ni layer instead of interacting with the liquid phase.The high reliability of the HEC/Nb_(2)Ni bonded interface was confirmed by the coherence of(11¯3)_(HEC)//(141)_(Nb_(2))Ni and a calculated lattice misfit of 0.044.The HEC joint had a high room-temperature strength of 174 MPa because of the homogenous Nb_(2)Ni layer,which exhibited nanohardness(15.2±1.5 GPa)and an elastic modulus of 219.9±17.5 GPa.Furthermore,the strength of the HEC joint did not decrease at 1000℃,increasing by~49%over that of HEC/Ni/HEC diffusion-bonded joints,which have stringent surface flatness requirements.This suggested that the HEC/Nb_(2)Ni interface had excellent resistance to high-temperature softening,even though it was invariably the initial failure location.This work is informative for designing bonding structures and preparing HEC components.展开更多
The design of microstructures is essential for tailoring the microwave dielectric properties of ceramics,yet the structure-property relationships in tetragonal scheelite-structured ceramics remain insufficiently under...The design of microstructures is essential for tailoring the microwave dielectric properties of ceramics,yet the structure-property relationships in tetragonal scheelite-structured ceramics remain insufficiently understood.In this study,first-principles calculations combined with experiments were used to systematically investigate the interrelations among the sintering behavior,crystal structure,electrical characteristics,bond characteristics,and dielectric performance of NaSrLnMo_(3)O_(12)(Ln=Ce,Pr,Eu,Y,and Yb)ceramics.All the compositions crystallized into a tetragonal scheelite structure(space group I41/a)and exhibited favorable dielectric properties with optimal sintering temperatures of 775-925℃,ε_(r)=9.8-10.34,Q×f=30,487-69,445 GHz,and τ_(f)=−20.55-(−44.24)ppm/℃.The increase inε_(r) originated mainly from the increased ionicity of the Na/Sr/Ln-O bonds,whereas the increase in Q×f was attributed to the increased lattice energy of the Mo-O bonds,increased bond valence,and reduced ionic/electricity disorder.The negative shift inτ_(f) was primarily linked to the increased linear thermal expansion coefficientαL of the Na/Sr/Ln-O bonds.Furthermore,the electrical characteristics and relaxation mechanisms were examined,and the dielectric response in the terahertz range was confirmed.Finally,NaSrCeMo_(3)O_(12) was employed to design and fabricate two antenna devices,verifying its potential for high-frequency communication.This work provides a systematic understanding of the role of Ln in optimizing the dielectric properties of tetragonal scheelite ceramics and clarifies the microscopic mechanisms underlying their performance.展开更多
With the rapid advancement of information technology,electromagnetic radiation has become deeply integrated into nearly every aspect of modern life,from personal communication and industrial manufacturing to aerospace...With the rapid advancement of information technology,electromagnetic radiation has become deeply integrated into nearly every aspect of modern life,from personal communication and industrial manufacturing to aerospace and national defense infrastructures.As the electromagnetic environment has become increasingly complex and congested,electromagnetic waves have not only brought unprecedented convenience but also introduced serious challenges,including electromagnetic interference,radiation pollution,and information insecurity.Consequently,the rational design and development of microwave absorption materials(MAMs)are critically important for protecting human health,mitigating electromagnetic pollution,and strengthening information security in the information age.展开更多
The stacking structure of Nb_(2)CSe_(2),a newly synthesized layered metal carbo-selenide,was elucidated by scanning transmission electron microscopy.Nb,CSe2 features Se-Nb-C-Nb-Se quintuple atomic layers.These layers ...The stacking structure of Nb_(2)CSe_(2),a newly synthesized layered metal carbo-selenide,was elucidated by scanning transmission electron microscopy.Nb,CSe2 features Se-Nb-C-Nb-Se quintuple atomic layers.These layers are stacked in Bernal mode.In this mode,Nb,CSe2 crystallizes in a trigonal symmetry(space group P3m1,No.164),with lattice parameters of a=3.33 A and c=18.20 A.Electronic structure calculations indicate that the metal carbo-selenide has Fermi energy crossing the bands where it touches to give a zero gap,indicating that it is an electronic conductor.As evidenced experimentally,the electrical conductivity is as high as 6.6×10^(5) S·m^(-1),outperforming the counterparts in the MXene family.Owing to the layered structure,the bonding in Nb_(2)CSe_(2) with an ionic formula of(Nb^(1.48+)),(C^(1.74-))(Se^(0.61-))_(2) is highly anisotropic,with metallic-covalent-ionic bonding in intralayers and weak bonding between interlayers.The layered nature is further evidenced by elastic properties,interlayer energy,and friction coefficient determination.These characteristics indicate that Nb_(2)CSe_(2) is an analog of molybdenum disulfide(MoS_(2)),which is a typical binary van der Waals(vdW)solid.Moreover,vibrational properties are reported,which may offer an optical identification standardfor new ternary vdW solids in spectroscopic studies,including Raman scatteringand infrared absorption.展开更多
CrB_(2)crystallizes in an AlB_(2)-type crystal structure,and the chemical bonding in CrB_(2)includes B sp^(2)‒B sp^(2)covalent bonds in the graphite-analogous six-numbered B ring,B p_(z)‒Cr 3d covalent‒ionic bonds,and...CrB_(2)crystallizes in an AlB_(2)-type crystal structure,and the chemical bonding in CrB_(2)includes B sp^(2)‒B sp^(2)covalent bonds in the graphite-analogous six-numbered B ring,B p_(z)‒Cr 3d covalent‒ionic bonds,and Cr‒Cr metallic bonds from theoretical calculations.However,the crystal structure and chemical bonding properties have not been experimentally validated.To fill this research gap,herein,the crystal structure and chemical bonding of CrB_(2)were evaluated for the first time via aberration-corrected transmission electron microscopy(AC-TEM)coupled with electron energy loss spectroscopy(EELS).Combined with first-principles calculations based on density functional theory(DFT),CrB_(2)is confirmed to have an AlB_(2)-type structure,where Cr bonds to each other in the(001)plane via metallic bonding and where B bonds in the form of a graphite-like six-membered ring in the(002)plane through sp^(2)hybridization,whereas Cr‒B ionic‒covalent bonding is formed in the(110)plane.A detailed analysis of the experimental and calculated results of the EELS of CrB_(2)shows that the hybridization of Cr 3d and B has a significant effect on the EELS of transition metal borides(TMB_(2)).In addition,the hysteresis loop of CrB_(2)was tested for the first time on the basis of theoretical calculations,and the molar susceptibility of CrB_(2)was approximately 5.77×10^(−4)emu/mol.The present work is helpful for understanding the structure‒property relationships,which are essential for tailoring the properties from a crystal structure and chemical bonding point of view and promoting the practical application of TMB_(2)in extreme aerospace environments.展开更多
Oxide scales grown on carbides or borides based ultrahigh thermal protection materials during service play crucial roles in the safe operation of the systems in extreme environments,where advancing technologies are pu...Oxide scales grown on carbides or borides based ultrahigh thermal protection materials during service play crucial roles in the safe operation of the systems in extreme environments,where advancing technologies are pushing temperature limits beyond 3000℃,exceeding the melting points of all known nonradioactive oxides.Although cationic solid solutions offer a pathway to modulate melting behavior,conventional phase diagrams show that most solid solutions exhibit lower melting points than their parent components.The mechanisms underlying melting point elevation in oxides have remained unclear.Here,we demonstrate a cationic design strategy for ultrahigh melting point oxides based on simultaneous control of the valence electron concentration,cation size,orbital overlap,coordination number and crystallographic symmetry.Using this approach,we developed a Ta-doped HfO2 solid solution with a melting point of 3006℃,the highest reported nonradioactive oxide,which represents an increase of nearly 150℃ over the parent oxide.This approach should be universally applicable to designing various ceramics with high or ultrahigh melting points.展开更多
To address the challenges of insufficient thermal resistance and high-temperature stability in current environmental barrier coating(EBC)bond coats above 1500℃,this study successfully synthesized HfO_(2)–Al_(2)O_(3)...To address the challenges of insufficient thermal resistance and high-temperature stability in current environmental barrier coating(EBC)bond coats above 1500℃,this study successfully synthesized HfO_(2)–Al_(2)O_(3)–SiO_(2) powders with a dispersion-strengthened structure for EBC bond coat raw material for spraying through a solid-phase synthesis method using HfO_(2),Al_(2)O_(3),and SiO_(2) sol.The dispersion-strengthened structure with a microstructure of oxides(HfO_(2) and Al_(2)O_(3))dispersed in silicates(mullite and HfSiO4)can be achieved by systematically adjusting the component molar ratios,synthesis temperature,and time.The synthesized raw powders underwent subsequent hightemperature hot-pressing sintering to form ceramic bulks,allowing for a comprehensive characterization of the intrinsic material properties,including thermal conductivity,coefficient of thermal expansion,mechanical performance,oxidation resistance at 1600℃,and water‒oxygen corrosion resistance at 1300℃.The investigation elucidates the property evolution and related mechanisms,conclusively demonstrating the viability of the HfO_(2)–Al_(2)O_(3)–SiO_(2) system as an EBC bond coating material.Additional chemical compatibility tests with SiO_(2) at 1500℃ further validated the dispersion-strengthened structure.Notably,oxidation resistance testing at 1600℃ revealed that Al_(2)O_(3) could better capture SiO_(2) generated by the decomposition of HfSiO4 to form mullite,thus enhancing the high-temperature stability of the HfO_(2)–Al_(2)O_(3)–SiO_(2) material,benefiting from its dispersion-strengthened structure.The present study establishes a robust theoretical foundation for the development of EBC bond coatings with exceptional high-temperature endurance exceeding 1500℃.展开更多
The development of high-strain piezoelectric materials has presented a longstanding challenge,particularly in the development of high-strain polycrystalline lead-free piezoelectric thin films.In this work,we present a...The development of high-strain piezoelectric materials has presented a longstanding challenge,particularly in the development of high-strain polycrystalline lead-free piezoelectric thin films.In this work,we present a strategy for customizing the electrostrain in lead-free thin films through phase transition engineering.In this study,we achieved a high recoverable electrostrain in a Bi_(1/2)Na_(1/2)TiO_(3)–BiAlO_(3)(BNT–BA)film.To accomplish this,ferroelectric BNT and BNT–BA films with identical thicknesses of 500 nm were fabricated on Pt(111)/TiO_(2)/SiO_(2)/Si(100)substrates via a sol-gel method.Compared with the BNT film,the BNT–BA film exhibited a greater polarization response and superior field strength endurance,maintaining the energy storage density beyond the breakdown field strength of the BNT.The BNT–BA film demonstrated a large unipolar strain of S=0.43%with a normalized strain(maximum strain/maximum applied electric field(S_(max)/E_(max)))of 203 pm/V,followed by an effective transverse piezoelectric coefficient(e∗31,f)of~2.48 C/m^(2),which was more than two times greater than the value obtained for BNT(i.e.,maximum strain/maximum applied electric field(S_(max)/E_(max))=72 pm/V and e^(∗)_(31,f)of~1.09 C/m^(2)).This high strain response in the BNT–BA film can be attributed to the electric-field-induced phase transition of the mixed(i.e.,cubic and rhombohedral)phases into rhombohedral and tetragonal phases(mainly the rhombohedral structure),which recover back to the original state when the electric field is removed.These findings suggest new pathways for achieving significant strain levels via alternative mechanisms,potentially enhancing the effectiveness and expanding the applications of piezoelectric materials.展开更多
The simultaneous optimization of the bulk and surface characteristics of photoelectrodes is essential to maximize their photoelectrochemical(PEC)performance.We report a novel one-pot hydrothermal synthesis of textured...The simultaneous optimization of the bulk and surface characteristics of photoelectrodes is essential to maximize their photoelectrochemical(PEC)performance.We report a novel one-pot hydrothermal synthesis of textured and surface-reconstructed BiVO_(4)photoanodes(ts-BVO),achieving significant improvements in PEC water splitting.By controlling precursor molarity and ethylene glycol(EG)addition,we developed a stepwise dual reaction(SDR)mechanism,which enables simultaneous bulk texture development and surface reconstruction.The optimized CoBi/ts-BVO photoanode exhibited a photocurrent density of 4.3 mA∙cm^(−2)at 1.23 V vs.reversible hydrogen electrode(RHE)with a high Faradaic efficiency of 98%under one sun illumination.Compared with nontextured BiVO_(4),the charge transport efficiency increased from 8%to 70%,whereas the surface charge transfer efficiency improved from 9%to 85%.These results underscore the critical role of both bulk and surface engineering in enhancing PEC performance.Our findings offer a streamlined approach for improving the intrinsic properties of photoanodes in solar water splitting.展开更多
The sintering trajectory of the Ho,Pr:Y_(2)O_(3) ceramics could be effectively adjusted by sintering in a flowing oxygen atmosphere instead of vacuum.The final-stage grain growth was significantly suppressed by the us...The sintering trajectory of the Ho,Pr:Y_(2)O_(3) ceramics could be effectively adjusted by sintering in a flowing oxygen atmosphere instead of vacuum.The final-stage grain growth was significantly suppressed by the use of oxygen atmosphere presintering,resulting in smaller average grain sizes than those of samples sintered under vacuum,while the same relative density was achieved.After hot isostatic pressing(HIP),the oxygen presintered Ho,Pr:Y_(2)O_(3) ceramics achieved excellent optical quality,with transmittance exceeding 80%at a wavelength of 680 nm.The codoping of Pr^(3+) as deactivating ions effectively depopulated the lower energy level 5I7 during the Ho^(3+):^(5)I_(6)→^(5)I_(7) transition,thereby making the Ho,Pr:Y_(2)O_(3) ceramics more conducive to promoting population inversion in the 2.9μm laser wavelength range.展开更多
Owing to their unique mechanical properties and excellent thermal and chemical stability,Al_(2)O_(3)nanofibers are highly desirable for practical applications as functional and structural building blocks.However,the s...Owing to their unique mechanical properties and excellent thermal and chemical stability,Al_(2)O_(3)nanofibers are highly desirable for practical applications as functional and structural building blocks.However,the scalable production of Al,O3 nanofibers has always faced significant challenges,namely,high cost and complicated processes.This work explores a feasible and straightforward dealloying strategy for the batch synthesis of Al_(2)O_(3)nanofibers.When a binary Al-Li alloy is immersed in alcohol,the alkoxide nanofibers spontaneously grow following the mechanism of boundary strain energy minimization.The results indicate that by dissolving Li in Al-Li alloys,the continuous exposure of a fresh Al surface renders the remaining unsaturated bonds of Al sufficiently reactive,providing the conditions for the subsequent reaction with alcohols and thus inducing the formation of alcohol-aluminum compounds.These nanofibers were calcined in air to obtain monocrystallineα-Al_(2)O_(3)and polycrystalline y-Al_(2)O_(3)nanofibers.We investigated the evolution of the alloy into nanofibers in dry ethanol and the influence of different Al-Li alloy compositions and calcination temperatures on the crystal structure and morphology of the resulting Al_(2)O_(3)nanofibers.The study revealed thatγ-Al_(2)O_(3)with diameters of approximately 50-80 nm and lengths of approximately 20-30μm andα-Al_(2)O_(3)with diameters of approximately 100-150 nm and lengths of approximately 15-20μm were successfully prepared via this technique route.The approach reported in this study is anticipated to open new paths for the efficient and economical synthesis of advanced metal oxide nanofibers and lay the foundation for their extensive application in current industrial sectors.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant Nos.52172083,62275105,12304443,52473262,and 52402192)the Zhejiang Province Key R&D Program:Vanguard and Leading Geese Projects(Grant No.2024C01190)+6 种基金the International Science&Technology Cooperation Program of Guangdong(Grant No.2021A0505030078)the Guangzhou Key Research and Development Program(Grant No.2023B03J1239)the Program for Innovative Research Team in University of Education System of Guangzhou(Grant No.202235404)financially supported by the Guangdong Basic and Applied Basic Research Foundation(Grant No.2022A1515110463)the Significant Science and Technology Projects of LongMen Laboratory in Henan Province(Grant No.231100220100)the Key Research and Development Program of Henan Province(Grant No.231111222200)the Key Scientific Research Projects of Higher Education Institutions in Henan Province(Grant No.25CY025)。
文摘Near-infrared phosphor-converted light-emitting diodes(NIR pc-LEDs),one of the most promising NIR light sources,have garnered significant attention owing to their compact structure,long lifetime and energy conservation.Despite these advantages,commercial NIR pc-LEDs employing pseudotransmission configurations,where the NIR phosphor and silicone composites are directly coated on blue LED chips,suffer from critical limitations in thermal management that severely deteriorate their NIR output performance.To address these intrinsic limitations,we developed an oxygen-coordination-competitive crystallization strategy to engineer high-transparencyβ-Ga_(2)O_(3):Cr^(3+)glass-ceramics(GC).This strategy leveraged the strong oxygen affinity of Ga^(3+)ions,which drove the directional migration and recombination of Ga^(3+)and O^(2-)ions within the isolated[GaO_(4)]tetrahedral network during thermal processing.This controlled phase evolution enabled localized crystallization of theβ-Ga_(2)O_(3):Cr^(3+)nanocrystals while maintaining high transparency.The optimizedβ-Ga_(2)O_(3):Cr^(3+)GC(0.4 mm thickness)achieved remarkable 81.2%NIR transmittance,approaching internal quantum efficiency(IQE≈100%)and high thermal stability(89%@423 K).When this hightransparencyβ-Ga_(2)O_(3):Cr^(3+)GC was employed as the NIR conversion material,the NIR GC-converted LEDs(GCc-LEDs)achieved 568 mW of NIR output power at a 500 mA drive current with a photoelectric conversion efficiency of 13%.The demonstrated performance metrics of NIR GCc-LEDs positioned this technology as an ideal NIR illumination source for next-generation point-of-care diagnostics,intelligent night vision systems,and nondestructive testing applications.
基金supported by the National Natural Science Foundation of China(Nos.52105233 and 52275366).
文摘To improve the high-temperature ablation resistance properties of Ta(W) refractory alloys, a novel ultra-high-temperature ceramic (UHTC) composite coating was prepared by combining the technological advantages of high-speed laser cladding (HSLC) and pack cementation (PC). First, the HSLC process was employed to fabricate a (Hf,Ta)C–Ta(W) UHTC–refractory metal composite coating that had metallurgical bonding with the Ta(W) substrate. Then, the PC process was utilized to transform the refractory metal phase in the coating into the corresponding refractory silicide (RMSi_(2)) phase. Consequently, the (Hf,Ta)C–TaSi_(2) UHTC composite coating was successfully prepared. This new coating was ablated at a heat flux density of 8.0 MW/m^(2) for 300 s at a surface temperature of 2300 ℃, and the structural integrity of the coating was retained. The linear ablation rate of the coating is −0.67 µm/s. The ablated coating exhibits three distinct oxide layers: a loose HfO_(2) top layer, a dense HfO_(2) middle layer, and a slightly oxidized (Hf,Ta)CxOy–Hf–Ta–O glassy layer. The synergistic effect of HfO_(2) and Hf–Ta–O glassy oxide film endows the coating with excellent anti-ablation resistance. This innovative design of the UHTC–RMSi_(2) composite coating provides robust protection to the Ta(W) substrate from ultra-high temperature ablation and mechanical scouring.
基金supported by the Guangxi Science and Technology Plan Project(No.Gui Ke AB22035043)the National Natural Science Foundation of China(Nos.52072301,52472078,52072202,and 52102058)+3 种基金the National Key R&D Program of China(No.2022YFB3504901)the Beijing Natural Science Foundation(No.2242046)the Guangdong Basic and Applied Basic Research Foundation(No.2023A1515011609)the State Key Laboratory of Materials Processing and Die and Mold Technology,Huazhong University of Science and Technology(No.P2023-003).
文摘Porous ceramics are lightweight materials with diverse pore structures and are widely applied in areas such as thermal insulation, sound absorption, filtration, catalysis, and energy storage. However, excessive shrinkage during the sintering process of porous ceramics leads to cracking and deterioration, posing significant challenges for achieving complex shapes. Despite its importance, the field of low sintering shrinkage porous ceramics has not received sufficient attention. This review systematically discusses the principles and progress in the development of low sintering shrinkage porous ceramics. First, we introduce the characteristics of various preparation methods, including partial sintering, particle-stabilized foaming, gel-casting, foam-gelcasting, and additive manufacturing (AM). We then explain three primary principles of low sintering shrinkage from the perspectives of the volume effect and mass transfer processes. This review focuses on the properties and applications of typical low sintering shrinkage ceramics such as mullite and alumina, particularly their mechanical properties and thermal conductivity as thermal insulation and ceramic cores. Finally, we summarize the current state and present future perspectives on low sintering shrinkage porous ceramics.
基金supported by the Joint Funds of the National Natural Science Foundation of China(No.U23B20115)the Fok Ying-Tong Education Foundation,China(No.171050)。
文摘A high voltage gradient(V_(g))of ZnO-based varistor ceramics is critical for realizing miniaturized and lightweight overvoltage protection devices.However,improving V_(g) of ZnObased varistor ceramics through conventional high-temperature sintering process remains a significant challenge.Here,we present a strategy to fabricate ultrahigh voltage-gradient ZnO-based varistor ceramics by combining cold sintering process/spark plasma sintering(CSP–SPS)with post-annealing process.Employing CSP–SPS,the ZnO-based varistor ceramics were initially densified at 300℃ and subsequently annealed at a low temperature of 700–900℃.CSP–SPS technique combined with a low annealing temperature enables the production of ZnO-based varistor ceramics with fine and homogeneous microstructures,while suppressing the volatilization of Bi-rich phases at grain boundaries.This approach achieves the ultrahigh V_(g) of~1832.71 V/mm,high nonlinear coefficient(α)of~106.69,and low leakage current density(J_(L))of less than 0.2μA/cm^(2).This work shows that the integration of CSP–SPS and post-annealing provides a promising way to design ZnO-based varistor ceramics with ultrahigh V_(g).
基金supported by the National Natural Science Foundation of China(No.52002153)the Postdoctoral Science Foundation of China(No.2021M701470)the Innovation/Entrepreneurship Program(No.JSSCTD202146)of Jiangsu Province.
文摘The reactive air brazing(RAB)process of ceramics was developed in the early 2000s because high-temperature electrochemical devices,such as solid oxide fuel cells(SOFCs),gas separators,reformers,and ion transport membrane systems,are increasingly emerging.Accordingly,the reactive air wetting(RAW)and RAB of oxide ceramics have been investigated.Starting from the introduction of the advantages of the RAB process,the thermal expansion coefficients(TECs)of related materials,and the estimation of the TECs of Ag-based composite fillers,the RAW and RAB of ceramics are reviewed by classifying the employed ceramic materials,which mainly include yttria-stabilized zirconia(YSZ),perovskite oxides,Al_(2)O_(3),and nonoxide ceramics.In particular,the RAW and RAB processes,interfacial microstructures,reaction products,and joint reliability(including joint strength,fracture energy,gas tightness,and high-temperature aging resistance)are highlighted for understanding interfacial behavior and joint performance and developing application-oriented brazing technology.Finally,some helpful conclusions are drawn after summarizing the RAB of oxide ceramics.The prospects for RAB of SiC and high-entropy oxide ceramics are proposed after summarizing the RAB of oxide and nonoxide ceramics,and several aspects are proposed for promoting the development and application of RAB technology.
基金supported by the National Natural Science Foundation of China(Nos.51977027 and 51967008)the Scientific and Technological Project of Yunnan Precious Metals Laboratory(Nos.YPML-2023050250,YPML-2022050206,YPML20240502061,YPML-20240502062,and YPML-20240502091).
文摘High operating temperatures generally degrade the luminous performance of color converters used in high-power,laser-driven white lighting systems.This study demonstrated that the operating temperature of LuAG:Ce films can be significantly reduced,particularly under high-power laser excitation near the saturation threshold.This improvement was achieved by enhancing the crystallinity and increasing the Ce^(3+)content in LuAG:Ce films.LuAG:Ce films,approximately 22.17μm in thickness,were deposited on sapphire substrates via spray pyrolysis techniques.The crystallinity was controlled by the annealing temperature,while the Ce^(3+)content was regulated by the annealing atmosphere.Compared with those with a crystallinity of 75.5%,the air-annealed films with a crystallinity of 87.4%exhibited a remarkable 95.6℃decrease in operating temperature under 18 W/mm^(2)blue laser excitation.Additionally,the incorporation of a higher Ce^(3+)content through CO annealing led to a further reduction in the operating temperature.By lowering the operating temperature,LuAG:Ce films on sapphire substrates exhibit enhanced luminous performance and thermal stability under prolonged high-power laser excitation,which could inspire the design and development of advanced color converters for laser lighting applications.
基金supported by the Shanghai Pujiang Program(No.2022PJD033)the Oceanic Interdisciplinary Program of Shanghai Jiao Tong University(No.SL2022MS013)the Key R&D Program of Zhejiang(No.2024SSYS0085).
文摘The development of aeroengine with a high thrust-weight ratio poses great challenges for current top-coating thermal barrier coatings (TBCs) and environmental barrier coatings (EBCs) in service. Medium/high-entropy ceramics are highly promising candidate material for advanced TBCs/EBCs owing to their low thermal conductivity, high melting point, high-temperature stability, and calcium–magnesium–alumino–silicate (CMAS) resistance. Most feedstock powder used for medium/high-entropy TBCs/EBCs is prepared via traditional spray drying, which cannot fully exploit the advantages of multicomponent ceramics. The density, sphericity, inner structure, and flowability of feedstock powder affect their melting state during the thermal spraying process, which strongly affects the microstructure and properties of the deposited coatings. Therefore, the deposited coatings exhibit phase segregation, amorphous phases, and microstructure defects owing to unpredictable variations in feedstock powder with random morphologies and structures. Here, the structure and properties of feedstock powder prepared by state-of-the-art granulation technologies and their influences on the deposited coatings were systematically investigated, which can provide guidance for configuration optimization of feedstock powder and the manufacturing accuracy of the deposited coating. This review aims to bridge the gap between cutting-edge ceramics and advanced engineering technologies, thus providing concrete background knowledge and crucial guidelines for designing and developing TBCs/EBCs.
文摘Defect engineering enables the efficient management of electromagnetic parameters and the enhancement of electromagnetic wave(EMW)absorption.In this study,(Fe_(1−x)Mn_(x))_(2)AlB_(2) transition metal boride(MAB)phases with a layered structure were prepared via Joule heating-driven ultrafast synthesis,and their EMW absorption properties were investigated.The experimental results demonstrate that the incorporation of Mn atoms at the M site can effectively modulate the impedance matching and EMW absorption properties of the material through the introduction of defects and lattice distortions.Notably,(Fe_(0.3)Mn_(0.7))_(2)AlB_(2) exhibits a reflection loss as high as−47.8 dB at 12.24 GHz,with a maximum effective absorption bandwidth of 4.16 GHz(10.24-14.40 GHz)at an ultrasmall thickness of 1.5 mm.This study provides a promising avenue for the development of excellent microwave-absorbing materials,which are essential for meeting the evolving requirements of advanced electronics.Additionally,this work offers a paradigm for enhancing other properties of MAB phases through defect engineering.
基金financial support from the National Natural Science Foundation of China(Nos.52072304 and 51872246)supported by the Creative Research Foundation of the Science and Technology on Thermostructural Composite Materials Laboratory.
文摘Wireless surface acoustic wave(SAW)sensors hold great promise for in-situ,real-time monitoring and accurately assessing the health status of hot-end components.However,the thin-film electrode as the SAW sensor core unit with excellent high-temperature conductivity,stability,and oxidation resistance is still a challenge,especially in harsh ultra-high-temperature environments.In this study,we employed a polymer-derived ceramic approach to fabricate smooth and dense SiHfBCN ceramic coatings on YCa_(4)O(BO_(3))_(3)/BN substrate.The composition,microstructural evolution,and room-temperature and high-temperature electrical conductivity of SiHfBCN ceramic coatings were investigated to reveal the mechanism for controlling electrical conductivity.The results indicate that the electrical conductivity of the SiHfBCN ceramic coating pyrolyzed at a lower temperature of 1200℃reaches an impressive high value of 291.55 S·m^(-1) at 1200℃in argon.Importantly,the results also demonstrate that the coating has remarkable high-temperature conductivity and excellent repeatability and durability.Therefore,the typical semiconducting behavior of SiHfBCN ceramic coatings highlights their potential as thin-film electrodes for SAW high-temperature sensors in high-temperature extreme environments.
基金the financial support from the National Natural Science Foundation of China(Nos.52175357 and 52222511).
文摘To obtain high-entropy carbide(HEC)joints with excellent high-temperature performance,a(HfZrTiTaNb)C HEC joint featuring a direct diffusion-bonded interface with a Nb-based interlayer was successfully fabricated at relatively low temperatures of 1150–1250℃for 60 min under 10 MPa.Starting from a modified Ni/Nb/Ni composite interlayer with a Nb content of>64 at%,an alloyed Nb_(2)Ni layer was constructed in situ by accelerating the directional diffusion of Ni atoms from the high-entropy interface into the remaining pure Nb through the Ni‒Nb eutectic liquid.Moreover,the excess liquid phase was squeezed out of the bonding region,ensuring the absence of Ni-based compounds.Leveraging the intrinsic interfacial stability and sluggish diffusion effect,the HEC with its original lattice structure,was capable of developing diffusion bonding with the Nb_(2)Ni layer instead of interacting with the liquid phase.The high reliability of the HEC/Nb_(2)Ni bonded interface was confirmed by the coherence of(11¯3)_(HEC)//(141)_(Nb_(2))Ni and a calculated lattice misfit of 0.044.The HEC joint had a high room-temperature strength of 174 MPa because of the homogenous Nb_(2)Ni layer,which exhibited nanohardness(15.2±1.5 GPa)and an elastic modulus of 219.9±17.5 GPa.Furthermore,the strength of the HEC joint did not decrease at 1000℃,increasing by~49%over that of HEC/Ni/HEC diffusion-bonded joints,which have stringent surface flatness requirements.This suggested that the HEC/Nb_(2)Ni interface had excellent resistance to high-temperature softening,even though it was invariably the initial failure location.This work is informative for designing bonding structures and preparing HEC components.
基金supported by the Natural Science Foundation of Shandong Province,China(No.ZR2025MS833)National Natural Science Foundation(No.52272126).
文摘The design of microstructures is essential for tailoring the microwave dielectric properties of ceramics,yet the structure-property relationships in tetragonal scheelite-structured ceramics remain insufficiently understood.In this study,first-principles calculations combined with experiments were used to systematically investigate the interrelations among the sintering behavior,crystal structure,electrical characteristics,bond characteristics,and dielectric performance of NaSrLnMo_(3)O_(12)(Ln=Ce,Pr,Eu,Y,and Yb)ceramics.All the compositions crystallized into a tetragonal scheelite structure(space group I41/a)and exhibited favorable dielectric properties with optimal sintering temperatures of 775-925℃,ε_(r)=9.8-10.34,Q×f=30,487-69,445 GHz,and τ_(f)=−20.55-(−44.24)ppm/℃.The increase inε_(r) originated mainly from the increased ionicity of the Na/Sr/Ln-O bonds,whereas the increase in Q×f was attributed to the increased lattice energy of the Mo-O bonds,increased bond valence,and reduced ionic/electricity disorder.The negative shift inτ_(f) was primarily linked to the increased linear thermal expansion coefficientαL of the Na/Sr/Ln-O bonds.Furthermore,the electrical characteristics and relaxation mechanisms were examined,and the dielectric response in the terahertz range was confirmed.Finally,NaSrCeMo_(3)O_(12) was employed to design and fabricate two antenna devices,verifying its potential for high-frequency communication.This work provides a systematic understanding of the role of Ln in optimizing the dielectric properties of tetragonal scheelite ceramics and clarifies the microscopic mechanisms underlying their performance.
文摘With the rapid advancement of information technology,electromagnetic radiation has become deeply integrated into nearly every aspect of modern life,from personal communication and industrial manufacturing to aerospace and national defense infrastructures.As the electromagnetic environment has become increasingly complex and congested,electromagnetic waves have not only brought unprecedented convenience but also introduced serious challenges,including electromagnetic interference,radiation pollution,and information insecurity.Consequently,the rational design and development of microwave absorption materials(MAMs)are critically important for protecting human health,mitigating electromagnetic pollution,and strengthening information security in the information age.
基金supported by the Shenyang National Laboratory for Materials Science,Institute of Metal Research,Chinese Academy of Sciences,Basic and Applied Basic Research Program of Guangdong Province(No.2021B0301030003)Ji Hua Laboratory(No.X210141TL210)。
文摘The stacking structure of Nb_(2)CSe_(2),a newly synthesized layered metal carbo-selenide,was elucidated by scanning transmission electron microscopy.Nb,CSe2 features Se-Nb-C-Nb-Se quintuple atomic layers.These layers are stacked in Bernal mode.In this mode,Nb,CSe2 crystallizes in a trigonal symmetry(space group P3m1,No.164),with lattice parameters of a=3.33 A and c=18.20 A.Electronic structure calculations indicate that the metal carbo-selenide has Fermi energy crossing the bands where it touches to give a zero gap,indicating that it is an electronic conductor.As evidenced experimentally,the electrical conductivity is as high as 6.6×10^(5) S·m^(-1),outperforming the counterparts in the MXene family.Owing to the layered structure,the bonding in Nb_(2)CSe_(2) with an ionic formula of(Nb^(1.48+)),(C^(1.74-))(Se^(0.61-))_(2) is highly anisotropic,with metallic-covalent-ionic bonding in intralayers and weak bonding between interlayers.The layered nature is further evidenced by elastic properties,interlayer energy,and friction coefficient determination.These characteristics indicate that Nb_(2)CSe_(2) is an analog of molybdenum disulfide(MoS_(2)),which is a typical binary van der Waals(vdW)solid.Moreover,vibrational properties are reported,which may offer an optical identification standardfor new ternary vdW solids in spectroscopic studies,including Raman scatteringand infrared absorption.
基金financially supported by the National Natural Science Foundation of China(Nos.U23A20562 and 52302074).
文摘CrB_(2)crystallizes in an AlB_(2)-type crystal structure,and the chemical bonding in CrB_(2)includes B sp^(2)‒B sp^(2)covalent bonds in the graphite-analogous six-numbered B ring,B p_(z)‒Cr 3d covalent‒ionic bonds,and Cr‒Cr metallic bonds from theoretical calculations.However,the crystal structure and chemical bonding properties have not been experimentally validated.To fill this research gap,herein,the crystal structure and chemical bonding of CrB_(2)were evaluated for the first time via aberration-corrected transmission electron microscopy(AC-TEM)coupled with electron energy loss spectroscopy(EELS).Combined with first-principles calculations based on density functional theory(DFT),CrB_(2)is confirmed to have an AlB_(2)-type structure,where Cr bonds to each other in the(001)plane via metallic bonding and where B bonds in the form of a graphite-like six-membered ring in the(002)plane through sp^(2)hybridization,whereas Cr‒B ionic‒covalent bonding is formed in the(110)plane.A detailed analysis of the experimental and calculated results of the EELS of CrB_(2)shows that the hybridization of Cr 3d and B has a significant effect on the EELS of transition metal borides(TMB_(2)).In addition,the hysteresis loop of CrB_(2)was tested for the first time on the basis of theoretical calculations,and the molar susceptibility of CrB_(2)was approximately 5.77×10^(−4)emu/mol.The present work is helpful for understanding the structure‒property relationships,which are essential for tailoring the properties from a crystal structure and chemical bonding point of view and promoting the practical application of TMB_(2)in extreme aerospace environments.
基金supported by the National Natural Science Foundation of China(Nos.U23A20562,52272060,52522203,52002001,and 52302074)Key Program of National Natural Science Foundation of China(No.52032003).
文摘Oxide scales grown on carbides or borides based ultrahigh thermal protection materials during service play crucial roles in the safe operation of the systems in extreme environments,where advancing technologies are pushing temperature limits beyond 3000℃,exceeding the melting points of all known nonradioactive oxides.Although cationic solid solutions offer a pathway to modulate melting behavior,conventional phase diagrams show that most solid solutions exhibit lower melting points than their parent components.The mechanisms underlying melting point elevation in oxides have remained unclear.Here,we demonstrate a cationic design strategy for ultrahigh melting point oxides based on simultaneous control of the valence electron concentration,cation size,orbital overlap,coordination number and crystallographic symmetry.Using this approach,we developed a Ta-doped HfO2 solid solution with a melting point of 3006℃,the highest reported nonradioactive oxide,which represents an increase of nearly 150℃ over the parent oxide.This approach should be universally applicable to designing various ceramics with high or ultrahigh melting points.
基金funded by the Jiangxi Provincial Natural Science Foundation(20232BAB204019)the National Natural Science Foundation of China(52272063)the Aeronautical Science Foundation of China(2024Z055056001).
文摘To address the challenges of insufficient thermal resistance and high-temperature stability in current environmental barrier coating(EBC)bond coats above 1500℃,this study successfully synthesized HfO_(2)–Al_(2)O_(3)–SiO_(2) powders with a dispersion-strengthened structure for EBC bond coat raw material for spraying through a solid-phase synthesis method using HfO_(2),Al_(2)O_(3),and SiO_(2) sol.The dispersion-strengthened structure with a microstructure of oxides(HfO_(2) and Al_(2)O_(3))dispersed in silicates(mullite and HfSiO4)can be achieved by systematically adjusting the component molar ratios,synthesis temperature,and time.The synthesized raw powders underwent subsequent hightemperature hot-pressing sintering to form ceramic bulks,allowing for a comprehensive characterization of the intrinsic material properties,including thermal conductivity,coefficient of thermal expansion,mechanical performance,oxidation resistance at 1600℃,and water‒oxygen corrosion resistance at 1300℃.The investigation elucidates the property evolution and related mechanisms,conclusively demonstrating the viability of the HfO_(2)–Al_(2)O_(3)–SiO_(2) system as an EBC bond coating material.Additional chemical compatibility tests with SiO_(2) at 1500℃ further validated the dispersion-strengthened structure.Notably,oxidation resistance testing at 1600℃ revealed that Al_(2)O_(3) could better capture SiO_(2) generated by the decomposition of HfSiO4 to form mullite,thus enhancing the high-temperature stability of the HfO_(2)–Al_(2)O_(3)–SiO_(2) material,benefiting from its dispersion-strengthened structure.The present study establishes a robust theoretical foundation for the development of EBC bond coatings with exceptional high-temperature endurance exceeding 1500℃.
基金support of the Priority Research Centers Program and the Basic Science Research Program through the National Research Foundation of Korea(NRF),funded by the Ministry of Education(Nos.NRF2019R1A6A1A11053838 and RS-2023-00245221)Aman Ullah acknowledges the support of the Higher Education Commission of Islamabad,Pakistan,under the National Research Program for Universities-NRPU(20-17573/NRPU/R&D/HEC/2021)Muhammad Sheeraz acknowledges support from the Basic Science Research Program through NRF(No.RS-2023-00249613).
文摘The development of high-strain piezoelectric materials has presented a longstanding challenge,particularly in the development of high-strain polycrystalline lead-free piezoelectric thin films.In this work,we present a strategy for customizing the electrostrain in lead-free thin films through phase transition engineering.In this study,we achieved a high recoverable electrostrain in a Bi_(1/2)Na_(1/2)TiO_(3)–BiAlO_(3)(BNT–BA)film.To accomplish this,ferroelectric BNT and BNT–BA films with identical thicknesses of 500 nm were fabricated on Pt(111)/TiO_(2)/SiO_(2)/Si(100)substrates via a sol-gel method.Compared with the BNT film,the BNT–BA film exhibited a greater polarization response and superior field strength endurance,maintaining the energy storage density beyond the breakdown field strength of the BNT.The BNT–BA film demonstrated a large unipolar strain of S=0.43%with a normalized strain(maximum strain/maximum applied electric field(S_(max)/E_(max)))of 203 pm/V,followed by an effective transverse piezoelectric coefficient(e∗31,f)of~2.48 C/m^(2),which was more than two times greater than the value obtained for BNT(i.e.,maximum strain/maximum applied electric field(S_(max)/E_(max))=72 pm/V and e^(∗)_(31,f)of~1.09 C/m^(2)).This high strain response in the BNT–BA film can be attributed to the electric-field-induced phase transition of the mixed(i.e.,cubic and rhombohedral)phases into rhombohedral and tetragonal phases(mainly the rhombohedral structure),which recover back to the original state when the electric field is removed.These findings suggest new pathways for achieving significant strain levels via alternative mechanisms,potentially enhancing the effectiveness and expanding the applications of piezoelectric materials.
基金supported by the National Research Foundation of Korea(NRF)grant funded by the Korean government(MSIT)(No.RS-2024-00335976)supported by the Korea Institute of Energy Technology Evaluation Planning(KETEP)from the Ministry of Trade,Industry,Energy(No.20214000000680).
文摘The simultaneous optimization of the bulk and surface characteristics of photoelectrodes is essential to maximize their photoelectrochemical(PEC)performance.We report a novel one-pot hydrothermal synthesis of textured and surface-reconstructed BiVO_(4)photoanodes(ts-BVO),achieving significant improvements in PEC water splitting.By controlling precursor molarity and ethylene glycol(EG)addition,we developed a stepwise dual reaction(SDR)mechanism,which enables simultaneous bulk texture development and surface reconstruction.The optimized CoBi/ts-BVO photoanode exhibited a photocurrent density of 4.3 mA∙cm^(−2)at 1.23 V vs.reversible hydrogen electrode(RHE)with a high Faradaic efficiency of 98%under one sun illumination.Compared with nontextured BiVO_(4),the charge transport efficiency increased from 8%to 70%,whereas the surface charge transfer efficiency improved from 9%to 85%.These results underscore the critical role of both bulk and surface engineering in enhancing PEC performance.Our findings offer a streamlined approach for improving the intrinsic properties of photoanodes in solar water splitting.
基金supported by the National Key R&D Program of China(No.2022YFB3605800)the National Natural Science Foundation of China(Nos.62105130,62075089,52372010,52422201,11654005,and 12234014)+4 种基金the Natural Science Foundation of Shandong Province(No.ZR2023ZD53)the Research Capability Elevation Program of Guangdong Province(No.2022ZDJS116)the National Science Foundation of Top Talent of SZTU(No.GDRC202302)the Innovation Program for Quantum Science and Technology(No.2021ZD0303200)the Shanghai Municipal Science and Technology Major Project(Nos.2019SHZDZX01,22DZ2229004).
文摘The sintering trajectory of the Ho,Pr:Y_(2)O_(3) ceramics could be effectively adjusted by sintering in a flowing oxygen atmosphere instead of vacuum.The final-stage grain growth was significantly suppressed by the use of oxygen atmosphere presintering,resulting in smaller average grain sizes than those of samples sintered under vacuum,while the same relative density was achieved.After hot isostatic pressing(HIP),the oxygen presintered Ho,Pr:Y_(2)O_(3) ceramics achieved excellent optical quality,with transmittance exceeding 80%at a wavelength of 680 nm.The codoping of Pr^(3+) as deactivating ions effectively depopulated the lower energy level 5I7 during the Ho^(3+):^(5)I_(6)→^(5)I_(7) transition,thereby making the Ho,Pr:Y_(2)O_(3) ceramics more conducive to promoting population inversion in the 2.9μm laser wavelength range.
基金supported by the National Natural Science Foundation of China(No.U2469213)the Beijing Natural Science Foundation(Nos.2252051 and 2234093)+1 种基金the Fundamental Research Funds for the Central Universities(No.2022XKRC016),the Hebei Natural Science Foundation(No.E2024105074)the Research Fund for Commercialization of Major Scientific and Technological Achievements of Hebei Province(No.22281006Z and 23267601Z).
文摘Owing to their unique mechanical properties and excellent thermal and chemical stability,Al_(2)O_(3)nanofibers are highly desirable for practical applications as functional and structural building blocks.However,the scalable production of Al,O3 nanofibers has always faced significant challenges,namely,high cost and complicated processes.This work explores a feasible and straightforward dealloying strategy for the batch synthesis of Al_(2)O_(3)nanofibers.When a binary Al-Li alloy is immersed in alcohol,the alkoxide nanofibers spontaneously grow following the mechanism of boundary strain energy minimization.The results indicate that by dissolving Li in Al-Li alloys,the continuous exposure of a fresh Al surface renders the remaining unsaturated bonds of Al sufficiently reactive,providing the conditions for the subsequent reaction with alcohols and thus inducing the formation of alcohol-aluminum compounds.These nanofibers were calcined in air to obtain monocrystallineα-Al_(2)O_(3)and polycrystalline y-Al_(2)O_(3)nanofibers.We investigated the evolution of the alloy into nanofibers in dry ethanol and the influence of different Al-Li alloy compositions and calcination temperatures on the crystal structure and morphology of the resulting Al_(2)O_(3)nanofibers.The study revealed thatγ-Al_(2)O_(3)with diameters of approximately 50-80 nm and lengths of approximately 20-30μm andα-Al_(2)O_(3)with diameters of approximately 100-150 nm and lengths of approximately 15-20μm were successfully prepared via this technique route.The approach reported in this study is anticipated to open new paths for the efficient and economical synthesis of advanced metal oxide nanofibers and lay the foundation for their extensive application in current industrial sectors.
