Tin sulfide(SnS)is a promising non-toxic thermoelectric(TE)material to replace SnSe(Se is toxic),due to its similar structure and low thermal conductivity(k)comparable to SnSe.However,the poor electrical conductivity(...Tin sulfide(SnS)is a promising non-toxic thermoelectric(TE)material to replace SnSe(Se is toxic),due to its similar structure and low thermal conductivity(k)comparable to SnSe.However,the poor electrical conductivity(s)of SnS results in lower TE performance.In this work,high pressure was utilized to regulate the electronic structure,thereby mediating the conflict of electron and phonon transport to optimize the TE performance.In situ measurements of thermoelectric properties for SnS under high pressure and high temperature revealed that although the Seebeck coefficient(S)and k slightly decrease with increasing pressure,the s dramatically increases with increasing pressure,finally increasing the dimensionless figure of merit(ZT).The s increases from 2135 S·m^(-1)to 83549 S·m^(-1)as the pressure increases from 1 GPa to 5 GPa at 325 K,representing an increase of an order of magnitude.The high s of SnS leads to an increase in the PF to 1436μW·m^(-1)·K^(-2)at 5 GPa and 652 K.The maximum ZT value of 0.77 at 5 GPa and 652 K was obtained,which is 4 times the maximum ZT under ambient pressure and is comparable to that of doped SnS.The increase in s is due to the fact that pressure modulates the band structure of SnS by narrowing the band gap from 1.013 eV to 0.712 eV.This study presents a valuable guide for searching new high TE performance materials using high pressure.展开更多
Luminescent metal-organic frameworks(MOFs)have garnered significant attention due to their structural tunability and potential applications in solid-state lighting,bioimaging,sensing,anticounterfeiting,and other field...Luminescent metal-organic frameworks(MOFs)have garnered significant attention due to their structural tunability and potential applications in solid-state lighting,bioimaging,sensing,anticounterfeiting,and other fields.Nevertheless,due to the tendency of1,4-benzenedicarboxylic acid(BDC)to rotate within the framework,MOFs composed of it exhibit significant non-radiative energy dissipation and thus impair the emissive properties.In this study,efficient luminescence of MIL-140A nanocrystals(NCs)with BDC rotors as ligands is achieved by pressure treatment strategy.Pressure treatment effectively modulates the pore structure of the framework,enhancing the interactions between the N,N-dimethylformamide vip molecules and the BDC ligands.The enhanced host-vip interaction contributes to the structural rigidity of the MOF,thereby suppressing the rotation-induced excited-state energy loss.As a result,the pressure-treated MIL-140A NCs displayed bright blue-light emission,with the photoluminescence quantum yield increasing from an initial 6.8%to 69.2%.This study developed an effective strategy to improve the luminescence performance of rotor ligand MOFs,offers a new avenue for the rational design and synthesis of MOFs with superior luminescent properties.展开更多
In thermoelectricity,the inherent coupling between electrical conductivity and Seebeck coefficient represents a fundamental challenge in thermoelectric materials development.Herein,we present a unique pressure-tuning ...In thermoelectricity,the inherent coupling between electrical conductivity and Seebeck coefficient represents a fundamental challenge in thermoelectric materials development.Herein,we present a unique pressure-tuning strategy using compressible layered 2H-MoTe2,achieving an effective decoupling between the electrical conductivity and Seebeck coefficient.The applied pressure simultaneously induces two complementary effects:(1)bandgap reduction that moderately enhances carrier concentration to improve the electrical conductivity,and(2)band convergence that dramatically increases density-of-states effective mass to boost the Seebeck coefficient.This dual mechanism yields an extraordinary 18.5-fold enhancement in the average power factor.First-principles calculations and Boltzmann transport modeling precisely reproduce the experimental observations,validating this pressure-induced decoupling mechanism.The pressure-tuning mechanism provides a feasible and effective strategy for breaking through the optimization limits of the power factor,facilitating the design of high-performance thermoelectric materials.展开更多
Low-dimensional hybrid metal halides exhibit broadband emission and high photoluminescence quantum yield(PLQY), making them promising candidates for the next-generation luminescent materials in lighting applications. ...Low-dimensional hybrid metal halides exhibit broadband emission and high photoluminescence quantum yield(PLQY), making them promising candidates for the next-generation luminescent materials in lighting applications. Here,the emission intensity of(C_(12)H_(24)O_(6))_(2)Na_(2)(H_(2)O)_(3)Cu_(4)I_(6) was strengthened between 9.3 GPa and 17.2 GPa, accompanied by the redshift of emission wavelength. The photoluminescence(PL) of Cu(Ⅰ)-based organometallic halides originates from multiple emission states, which are a metal-to-ligand charge transfer or a halide-to-ligand charge transfer(MLCT/HLCT)excited state and a cluster-centered(CC) excited state. MLCT/HLCT-related emission wavelength redshifts while CCrelated emission wavelength remains unchanged, indicating that the rearrangement of different emission states plays a critical role in the changes of luminescence wavelength. This study not only deepens the understanding of the influence of high pressure on(C_(12)H_(24)O_(6))_(2)Na_(2)(H_(2)O)_(3)Cu_(4)I_(6), but also provides valuable insights into the structure–property relationship of zero-dimensional Cu(Ⅰ)-based organometallic halides.展开更多
The structural phase transition of MnO_(2) nanorods was investigated using in situ high pressure synchrotron x-ray diffraction(XRD) and transmission electron microscopy(TEM). At pressures exceeding 10.9 GPa, a second-...The structural phase transition of MnO_(2) nanorods was investigated using in situ high pressure synchrotron x-ray diffraction(XRD) and transmission electron microscopy(TEM). At pressures exceeding 10.9 GPa, a second-order structural phase transition from tetragonal to orthogonal, which was accompanied by fine-scale crystal twinning phenomena, was observed in MnO_(2) nanorods. On account of the significant contribution of surface energy, the phase transition pressure exhibited appreciable hysteresis compared with the bulk counterparts, suggesting the enhanced structural stability of nanorod morphology. These findings reveal that the size and morphology exhibit a manifest correlation with the high pressure behavior of MnO_(2) nanomaterials, providing useful insights into the intricate interplay between structure and properties.展开更多
The ability to generate high pressures in a large-volume press(LVP)is crucial for the study of matter under extreme conditions.Here,we have achieved ultrahigh pressures of and 50 GPa,respectively,at room temperature a...The ability to generate high pressures in a large-volume press(LVP)is crucial for the study of matter under extreme conditions.Here,we have achieved ultrahigh pressures of and 50 GPa,respectively,at room temperature and a high temperature of 1900 K∼60within a millimeter-sized sample volume in a Kawai-type LVP(KLVP)using hard tungsten carbide(WC)and newly designed assem-blies.The introduction of electroconductive polycrystalline boron-doped diamond and dense alumina wrapped with Cu foils into a large conventional cell assembly enables the detection of resistance variations in the Fe_(2)O_(3) pressure standard upon compression.The efficiency of pressure generation in the newly developed cell assembly equipped with conventional ZK10F WC anvils is significantly higher than that of conventional assemblies with some ultrahard or tapered WC anvils.Our study has enabled the routine gener-ation of pressures exceeding 50 GPa within a millimeter-sized sample chamber that have been inaccessible with traditional KLVPs.This advance in high-pressure technology not only breaks a record for pressure generation in traditional KLVPs,but also opens up new avenues for exploration of the properties of the Earth’s deep interior and for the synthesis of novel materials at extreme high pressures.展开更多
High pressure enables the creation of novel functional materials by modifying chemical bonding and crystal structure,opening avenues for the development of high-energy-density polynitrogen materials.We present the hig...High pressure enables the creation of novel functional materials by modifying chemical bonding and crystal structure,opening avenues for the development of high-energy-density polynitrogen materials.We present the high-pressure synthesis of three polynitrides P1 AgN7,P21/c AgN5,and P-1 AgN4,achieved through direct reactions between silver and nitrogen.Notably,the synthesis pressures required for the formation of N5 and N6 rings from metal–nitrogen reactions in this work represent the lowest values reported to date in high-pressure studies.At 15 GPa,isolated N5 rings are stabilized in P1 AgN7 and P21/c AgN5.At 26.3 GPa,P-1 AgN4 is synthesized,featuring infinite onedimensional nitrogen chains composed of alternating N2 and N6 rings,a unique catenation not observed in other polynitrides.In addition,AgN7,AgN5,and AgN4 possess significantly higher volumetric energy densities Ev than the conventional explosive TNT,making them promising high-energy-density materials.展开更多
The discovery of high-temperature superconductivity in bilayer nickelate La_(3)Ni_(2)O_(7)under high-pressure conditions has spurred extensive efforts to stabilize superconductivity at ambient pressure.Recently,the re...The discovery of high-temperature superconductivity in bilayer nickelate La_(3)Ni_(2)O_(7)under high-pressure conditions has spurred extensive efforts to stabilize superconductivity at ambient pressure.Recently,the realization of superconductivity in compressively strained La_(3)Ni_(2)O_(7)thin films grown on the SrLaAlO_(4)substrates,with a T_(c)exceeding 40 K,represents a significant step toward this goal.Here,we investigate the influence of film thickness and carrier doping on the electronic structure of La_(3)Ni_(2)O_(7)thin films,ranging from 0.5 to 3 unit cells,using first-principles calculations.For a 2 unit-cell film with an optimal doping concentration of 0.3 hole per formula unit(0.15 hole/Ni),the Ni-d_(z^(2))interlayer bonding state crosses the Fermi level,resulting in the formation ofγpockets at the Fermi surface.These findings align with angle-resolved photoemission spectroscopy experimental data.Our results provide theoretical validation for the recent experimental discovery of ambient-pressure superconductivity in La_(3)Ni_(2)O_(7)thin films and underscore the significant impact of film thickness and carrier doping on electronic property modulation.展开更多
Phase engineering has proven to be an effective strategy for achieving superior thermoelectric performance,while pressure is an excellent means of expanding the phase space of a material.In this paper,the effect of pr...Phase engineering has proven to be an effective strategy for achieving superior thermoelectric performance,while pressure is an excellent means of expanding the phase space of a material.In this paper,the effect of pressure-induced phase transition on improving the crystal symmetry and enhancing the thermoelectric properties of AgCrSe2 under high pressure and high temperature are reported.A structural phase transition from the low-symmetry R3m phase to the high-symmetry P3m1 phase is discovered below 1 GPa,which increases band degeneracy and contributes to a high electrical conductivity.For the metallic P3m1 phase,the electrons surrounding the Se2−anion gradually transfer to the Ag+and Cr3+cations as the pressure increases,decreasing the density of states around the Fermi level and thus optimizing the carrier concentration,thereby increasing the Seebeck coefficient while maintaining a high electrical conductivity.Consequently,an ultrahigh power factor of 864μW⋅m−1⋅K−2 is achieved at 5 GPa and 297 K.This study provides new insights into improving thermoelectric transport properties by applying physical pressure to enhance crystal symmetry and optimize thermoelectric parameters,and also indicates that phase engineering is a compelling strategy to discover or design novel high-performance thermoelectric materials starting from low-symmetry compounds.展开更多
Continuously improving the mechanical properties of ultra-high-temperature ceramics(UHTCs)is a key requirement for their future applications.However,the mechanical properties of conventional UHTCs,HfB_(2) and ZrB_(2),...Continuously improving the mechanical properties of ultra-high-temperature ceramics(UHTCs)is a key requirement for their future applications.However,the mechanical properties of conventional UHTCs,HfB_(2) and ZrB_(2),remain unsatisfactory among transition metal light-element(TMLE)compounds.TiB_(2) has superior mechanical properties compared to both HfB_(2) and ZrB_(2),but suffers from inherent brittleness and limited oxidation resistance.In this work,low-content solidsolution strengthening was used to fabricate dense samples of Tix(Hf/Zr)_(1-x)B_(2)(THZ)under high pressure and high temperature(HPHT).Compared to pure TiB_(2),Ti_(0.94)(Hf/Zr)0.06B_(2) exhibits a significant 38.8%increase in oxidation resistance temperature(950℃),while Ti_(0.91)(Hf/Zr)_(0.09)B_(2) shows a notable 28%enhancement in fracture toughness(5.8 MPa·m^(1/2)).The synergistic effect of a dual-atom solid-solution results in local internal stress and anomalous lattice contraction.This lattice contraction helps resist oxygen invasion,thereby elevating the oxidation resistance threshold.Additionally,the internal stress induces crack deflection within individual grains,enhancing toughness through energy dissipation.This work provides a new strategy for fabricating robust UHTCs within TMLE systems,demonstrating significant potential for future high-temperature applications.展开更多
High-mobility semiconductor nanotubes have demonstrated great potential for applications in high-speed transistors,single-charge detection,and memory devices.Here we systematically investigated the electronic properti...High-mobility semiconductor nanotubes have demonstrated great potential for applications in high-speed transistors,single-charge detection,and memory devices.Here we systematically investigated the electronic properties of single-walled boron antimonide(BSb)nanotubes using first-principles calculations.We observed that rolling the hexagonal boron antimonide monolayer into armchair(ANT)and zigzag(ZNT)nanotubes induces compression and wrinkling effects,significantly modifying the band structures and carrier mobilities through band folding andπ^(*)-σ^(*)hybridization.As the chiral index increases,the band gap and carrier mobility of ANTs decrease monotonically,where electron mobility consistently exceeds hole mobility.In contrast,ZNTs exhibit a more complex trend:the band gap first increases and then decreases,and the carrier mobility displays oscillatory behavior.In particular,both ANTs and ZNTs could exhibit significantly higher carrier mobilities compared to hexagonal monolayer and zinc-blende BSb,reaching 10^(-3)-10^(-7) cm^(-2)·V^(-1)·s^(-1).Our findings highlight strong curvature-induced modifications in the electronic properties of single-walled BSb nanotubes,demonstrating the latter as a promising candidate for high-performance electronic devices.展开更多
Lonsdaleite,also known as hexagonal diamond,is an allotrope of carbon with a hexagonal crystal structure,which was discovered in the nanostructure of the Canyon Diablo meteorite.Theoretical calculations have shown tha...Lonsdaleite,also known as hexagonal diamond,is an allotrope of carbon with a hexagonal crystal structure,which was discovered in the nanostructure of the Canyon Diablo meteorite.Theoretical calculations have shown that this structure gives it exceptional physical properties that exceed those of cubic diamond,making it highly promising for groundbreaking applications in superhard cutting tools,wide-bandgap semiconductor devices,and materials for extreme environments.As a result,the controllable synthesis of hexagonal diamond has emerged as a cutting-edge research focus in materials science.This review briefly outlines the progress in this area,with a focus on the mechanisms governing its key synthesis conditions,its intrinsic physical properties,and its potential applications in various fields.展开更多
Ternary hydrides, with their superior chemical and structural flexibility over binary systems, open up new avenues for advancing high-performance superconductor research. The Y-Ca-H system is a promising candidate for...Ternary hydrides, with their superior chemical and structural flexibility over binary systems, open up new avenues for advancing high-performance superconductor research. The Y-Ca-H system is a promising candidate for high-temperature superconductors, as both Im3m YH_(6) and Im3m CaH_(6) exhibit similar structures and excellent superconducting properties, while Y and Ca atoms possess close atomic radii and electronegativities.Here, we report the successful synthesis of Im3m(Y, Ca)H_(6) achieving a maximum superconducting transition temperature(T_(c)) approximately 224 K at 155 GPa through five independent high-temperature and high-pressure experiments. Remarkably, the T_(c) of Im3m(Y, Ca)H_(6) remains highly stable(ΔT_(c) ≤ 1 K) during decompression between 148 and 165 GPa, significantly outperforming binary Im3m CaH_(6) and Im3m YH_(6). The enhanced superconducting properties may stem from the cooperative chemical template effect of Y and Ca atoms near the s-d border, which significantly reinforces H lattice stability and thus maintains superior superconductivity.This study highlights the potential of multicomponent cooperative effects in designing hydride superconductors,offering new insights for achieving high-T_(c) hydrides at lower pressures in the future.展开更多
The discovery of pressure-induced superconducting electrides has sparked a intense wave of interest in novel superconductors.However,opinions vary regarding the relationship between non-nuclear attractors(NNAs)and sup...The discovery of pressure-induced superconducting electrides has sparked a intense wave of interest in novel superconductors.However,opinions vary regarding the relationship between non-nuclear attractors(NNAs)and superconductivity,with two opposing views currently represented by the materials Li_(6)P and Li_(6)C.Here,we choose the ternary Li–C–P as a model system and reveal the underlying mechanism by which NNAs contribute to superconductivity.The loosely bound NNAs in the superlithide Li_(14)CP covalently bond with Li and form unique satellite interstitial electrons(SIEs)around Li near the Fermi level,dominating the superconductivity.First-principles calculations show that the SIEs progressively increase in number and couple strongly with phonons at high pressure.Moreover,the Fermi surface nesting associated with SIEs induces phonon softening,further enhancing the electron–phonon coupling and giving the superlithide Li_(14)CP a T_(c)of 10.6 K at 300 GPa.The leading role of SIEs in superconductivity is a general one and is also relevant to the recently predicted Li_(6)P and Li_(6)C.Our work presented here reshapes the understanding of NNA-dominated superconductivity and holds promise for guiding future discoveries and designs of novel high-temperature superconductors.展开更多
Electrically conductive carbide ceramics with high hardness and fracture toughness are promising for advanced applications.However,enhancing both electrical conductivity and fracture toughness simultaneous is challeng...Electrically conductive carbide ceramics with high hardness and fracture toughness are promising for advanced applications.However,enhancing both electrical conductivity and fracture toughness simultaneous is challenging.This study reports the synthesis of(Ti_(0.2)W_(0.2)Ta_(0.2)Hf_(0.2)Mo_(0.2))C-diamond composites with varying densities using high-pressure and high-temperature(HPHT)method.The carbides are uniformly dispersed in a titanium carbide matrix,forming conductive channels that reduce resistivity to 4.6×10^(-7)W·m.These composite materials exhibit metallic conductivity with a superconducting transition at 8.5 K.Superconducting behavior may result from d-p orbital hybridization and electron-phonon coupling in transition metal carbides,such as TaC,Mo_(2)C,and MoC.Optimizing intergranular bonding improves the fracture toughness without compromising hardness.The highest indentation toughness value is 10.1±0.4 MPa·m^(1/2),a 130%increase compare to pure TiC.Enhanced toughness arises from transgranular and intergranular fracture modes,multiple crack bridging,and large-angle crack deflection,which dissipate fracture energy and inhibit crack propagation.This study introduces a novel microstructure engineering strategy for carbide ceramics to achieve superior mechanical and electrical properties.展开更多
Electrides,characterized by spatially confined anionic electrons,have emerged as a promising class of materials for catalysis,magnetism,and superconductivity.However,transition-metal-based electrides with diverse elec...Electrides,characterized by spatially confined anionic electrons,have emerged as a promising class of materials for catalysis,magnetism,and superconductivity.However,transition-metal-based electrides with diverse electron dimensionalities remain largely unexplored.Here,we perform a comprehensive first-principles investigation of Y-Co electrides,focusing on Y_(3)Co,Y_(3)Co_(2),and YCo.Our calculations reveal a striking dimensional evolution of anionic electrons:from two-dimensional(2D)confinement in YCo to one-dimensional(1D)in Y_(3)Co_(2)and zero-dimensional(0D)in Y_(3)Co.Remarkably,the YCo monolayer exhibits intrinsic ferromagnetism,with a magnetic moment of 0.65μB per formula unit arising from spin-polarized anionic electrons mediating long-range coupling between Y and Co ions.The monolayer also shows a low exfoliation energy(1.66 J/m^(2)),indicating experimental feasibility.All three electrides exhibit low work functions(2.76 eV-3.11 eV)along with Co-centered anionic states.This work expands the family of transition-metal-based electrides and highlights dimensionality engineering as a powerful strategy for tuning electronic and magnetic properties.展开更多
We report first-principles predictions of a cage-like polymeric nitrogen phase(cage-N)composed of interlocked N10 clusters stabilized by mixed sp^(2)/sp^(3) hybridization.Under high pressure,cage-N exhibits exceptiona...We report first-principles predictions of a cage-like polymeric nitrogen phase(cage-N)composed of interlocked N10 clusters stabilized by mixed sp^(2)/sp^(3) hybridization.Under high pressure,cage-N exhibits exceptional mechanical performance,including an ideal compressive strength of 343 GPa at a pressure of 300 GPa,~33% higher than that of diamond.This ultrahigh strength arises from the synergistic interplay between its three-dimensional covalent framework and hybridized bonding topology,which enables isotropic stress accommodation and dynamic electronic rearrangement.These results establish cage-N as a promising non-carbon ultrahard material and provide a bonding-driven route toward designing superhard frameworks under extreme conditions.展开更多
The chemical synthesis of functional materials is inseparable from national defense,medical treatment,national economy,and people’s livelihood.Traditional organic and inorganic materials are approaching their perform...The chemical synthesis of functional materials is inseparable from national defense,medical treatment,national economy,and people’s livelihood.Traditional organic and inorganic materials are approaching their performance limit.Therefore,the design and exploitation of novel functional materials are imminent and of significance for sustainable development.This review outlines the current progress and future prospects of chemical synthesis driven by high pressure,including organic and inorganic synthesis,as well as high-pressure phase retention.Based on the latest works,the basic mechanism of high-pressure chemical synthesis and three potential strategies for high-pressure phase harvesting are revealed.Finally,the challenge and outlook of high-pressureguided chemical synthesis are summarized.We sincerely hope that this review will provide guidance for designing high-performance materials by expanding the paths of chemical synthesis,thus greatly exploiting the existing materials world with newly emerging and enhanced functionalities.展开更多
Conventional hard and superhard materials,such as diamond and cubic boron nitride,are attractive for both scientific and industrial applications,but their intrinsically poor electrical conductivity limits broader use....Conventional hard and superhard materials,such as diamond and cubic boron nitride,are attractive for both scientific and industrial applications,but their intrinsically poor electrical conductivity limits broader use.This motivates the exploration of novel materials that combine superior hardness with excellent superconductivity.Herein,we performed a comprehensive structure search of the B–C system under pressures ranging from 0 to 100 GPa using machine-learning-potential(attention-coupled neural network,ACNN)based crystal structure prediction(CALYPSO).A stable BC 19 phase was identified at 50 GPa,featuring a diamond-like covalent framework with metallic character.Interestingly,BC 19 shows anisotropic superconductivity with an estimated superconducting critical temperature(T c)of 24 K at ambient pressure.Further analysis indicates that the high superconductivity of BC 19 originates from the strong coupling between theσelectrons and stretching vibrations of the covalent B–C framework.Additionally,BC 19 demonstrates superhard characteristics with a Vickers hardness of 76 GPa,exceeding that of cubic boron nitride.These results suggest that pressure-stabilized BC 19 represents a promising theoretical candidate for concurrent superconductivity and ultrahard mechanical performance.展开更多
Diamond has the strongest three-dimensional network structure and its cubic configuration is extremely stable under high pressure,thus limiting the experimental synthesis of diamond polymorphs.Hexagonal diamond,a typi...Diamond has the strongest three-dimensional network structure and its cubic configuration is extremely stable under high pressure,thus limiting the experimental synthesis of diamond polymorphs.Hexagonal diamond,a typical polymorph of diamond,has attracted considerable attention in recent decades,yet synthesizing pure and large-sized hexagonal diamond remains technically challenging,preventing an accurate understanding of its properties and formation mechanism.Here,we report the direct synthesis of millimeter-sized,nearly pure hexagonal diamond from graphite under high-pressure and high-temperature conditions using our developed high-pressure technique in a multi-anvil press.The synthesized hexagonal diamond is highly oriented polycrystalline,exhibiting an ultrahard hardness(165±4 GPa)on(100)planes,which is∼50%harder than single-crystal cubic diamond.Structural characterizations and molecular dynamics simulations indicate that hexagonal diamond is formed through a martensitic transformation process whereby hexagonal graphite is transformed into hexagonal diamond by sliding and then direct bonding between graphite sheets.Furthermore,we show that the transformations from graphite to cubic or hexagonal diamonds are strongly temperature-pressure dependent.With this understanding,we further synthesized cubic/hexagonal diamond composites with unusual heterostructures at a lower pressure.This work not only established a fundamental framework for high-pressure phase transformations in graphite but also provided insight into the structural evolution of two-dimensional materials at high pressures and a potent strategy for exploring their new high-pressure phases.展开更多
基金support from the Program for the Development of Science and Technology of Jilin Province(Grant No.SKL202402004)the Jilin Province Major Science and Technology Program(Grant No.20240211002GX)the Open Research Fund of the Key Laboratory of Functional Materials Physics and Chemistry of the Ministry of Education(Jilin Normal University,202405).
文摘Tin sulfide(SnS)is a promising non-toxic thermoelectric(TE)material to replace SnSe(Se is toxic),due to its similar structure and low thermal conductivity(k)comparable to SnSe.However,the poor electrical conductivity(s)of SnS results in lower TE performance.In this work,high pressure was utilized to regulate the electronic structure,thereby mediating the conflict of electron and phonon transport to optimize the TE performance.In situ measurements of thermoelectric properties for SnS under high pressure and high temperature revealed that although the Seebeck coefficient(S)and k slightly decrease with increasing pressure,the s dramatically increases with increasing pressure,finally increasing the dimensionless figure of merit(ZT).The s increases from 2135 S·m^(-1)to 83549 S·m^(-1)as the pressure increases from 1 GPa to 5 GPa at 325 K,representing an increase of an order of magnitude.The high s of SnS leads to an increase in the PF to 1436μW·m^(-1)·K^(-2)at 5 GPa and 652 K.The maximum ZT value of 0.77 at 5 GPa and 652 K was obtained,which is 4 times the maximum ZT under ambient pressure and is comparable to that of doped SnS.The increase in s is due to the fact that pressure modulates the band structure of SnS by narrowing the band gap from 1.013 eV to 0.712 eV.This study presents a valuable guide for searching new high TE performance materials using high pressure.
基金supported by the National Key R&D Program of China(Grant No.2023YFA1406200)the National Natural Science Foundation of China(No.12274177 and 12304261)the China Postdoctoral Science Foundation(No.2024M751076)。
文摘Luminescent metal-organic frameworks(MOFs)have garnered significant attention due to their structural tunability and potential applications in solid-state lighting,bioimaging,sensing,anticounterfeiting,and other fields.Nevertheless,due to the tendency of1,4-benzenedicarboxylic acid(BDC)to rotate within the framework,MOFs composed of it exhibit significant non-radiative energy dissipation and thus impair the emissive properties.In this study,efficient luminescence of MIL-140A nanocrystals(NCs)with BDC rotors as ligands is achieved by pressure treatment strategy.Pressure treatment effectively modulates the pore structure of the framework,enhancing the interactions between the N,N-dimethylformamide vip molecules and the BDC ligands.The enhanced host-vip interaction contributes to the structural rigidity of the MOF,thereby suppressing the rotation-induced excited-state energy loss.As a result,the pressure-treated MIL-140A NCs displayed bright blue-light emission,with the photoluminescence quantum yield increasing from an initial 6.8%to 69.2%.This study developed an effective strategy to improve the luminescence performance of rotor ligand MOFs,offers a new avenue for the rational design and synthesis of MOFs with superior luminescent properties.
基金supported by the Science and Technology Development Project of Jilin Province(Grant No.SKL202402004)the Program for the Development of Science and Technology of Jilin Province(Grant No.YDZJ202201ZYTS308)+1 种基金the Open Research Fund of State Key Laboratory of Inorganic Synthesis and Preparative Chemistry,Jilin University(Grant Nos.202216 and 2022-23)the National Natural Science Foundation of China(Grant No.12350410372)。
文摘In thermoelectricity,the inherent coupling between electrical conductivity and Seebeck coefficient represents a fundamental challenge in thermoelectric materials development.Herein,we present a unique pressure-tuning strategy using compressible layered 2H-MoTe2,achieving an effective decoupling between the electrical conductivity and Seebeck coefficient.The applied pressure simultaneously induces two complementary effects:(1)bandgap reduction that moderately enhances carrier concentration to improve the electrical conductivity,and(2)band convergence that dramatically increases density-of-states effective mass to boost the Seebeck coefficient.This dual mechanism yields an extraordinary 18.5-fold enhancement in the average power factor.First-principles calculations and Boltzmann transport modeling precisely reproduce the experimental observations,validating this pressure-induced decoupling mechanism.The pressure-tuning mechanism provides a feasible and effective strategy for breaking through the optimization limits of the power factor,facilitating the design of high-performance thermoelectric materials.
基金Project supported by the National Key R&D Program of China (Grant No. 2023YFA1406200)the National Natural Science Foundation of China (Grant Nos. 12174144 and 12474009)the Graduate Innovation Fund of Jilin University (Grant No. 2024CX201)。
文摘Low-dimensional hybrid metal halides exhibit broadband emission and high photoluminescence quantum yield(PLQY), making them promising candidates for the next-generation luminescent materials in lighting applications. Here,the emission intensity of(C_(12)H_(24)O_(6))_(2)Na_(2)(H_(2)O)_(3)Cu_(4)I_(6) was strengthened between 9.3 GPa and 17.2 GPa, accompanied by the redshift of emission wavelength. The photoluminescence(PL) of Cu(Ⅰ)-based organometallic halides originates from multiple emission states, which are a metal-to-ligand charge transfer or a halide-to-ligand charge transfer(MLCT/HLCT)excited state and a cluster-centered(CC) excited state. MLCT/HLCT-related emission wavelength redshifts while CCrelated emission wavelength remains unchanged, indicating that the rearrangement of different emission states plays a critical role in the changes of luminescence wavelength. This study not only deepens the understanding of the influence of high pressure on(C_(12)H_(24)O_(6))_(2)Na_(2)(H_(2)O)_(3)Cu_(4)I_(6), but also provides valuable insights into the structure–property relationship of zero-dimensional Cu(Ⅰ)-based organometallic halides.
基金Project supported by China Postdoctoral Science Foundation (Grant No. 2023M742049)Guangdong Basic and Applied Basic Research Foundation (Grant No. 2023A1515110844)the Innovative Training Program for College Students (Grant No. 20249076)。
文摘The structural phase transition of MnO_(2) nanorods was investigated using in situ high pressure synchrotron x-ray diffraction(XRD) and transmission electron microscopy(TEM). At pressures exceeding 10.9 GPa, a second-order structural phase transition from tetragonal to orthogonal, which was accompanied by fine-scale crystal twinning phenomena, was observed in MnO_(2) nanorods. On account of the significant contribution of surface energy, the phase transition pressure exhibited appreciable hysteresis compared with the bulk counterparts, suggesting the enhanced structural stability of nanorod morphology. These findings reveal that the size and morphology exhibit a manifest correlation with the high pressure behavior of MnO_(2) nanomaterials, providing useful insights into the intricate interplay between structure and properties.
基金supported by the National Key R&D Program of China(Grant No.2023YFA1406200)the National Natural Science Foundation of China(Grant Nos.42272041 and 52302043)+2 种基金the National Natural Science Foundation of China(Grant No.U23A20561)the Jilin University High-level Innovation Team Foundation(Grant No.2021TD–05)the Shanghai Synchrotron Radiation Facility(Grant Nos.2024-SSRF-PT-510031 and 505511).
文摘The ability to generate high pressures in a large-volume press(LVP)is crucial for the study of matter under extreme conditions.Here,we have achieved ultrahigh pressures of and 50 GPa,respectively,at room temperature and a high temperature of 1900 K∼60within a millimeter-sized sample volume in a Kawai-type LVP(KLVP)using hard tungsten carbide(WC)and newly designed assem-blies.The introduction of electroconductive polycrystalline boron-doped diamond and dense alumina wrapped with Cu foils into a large conventional cell assembly enables the detection of resistance variations in the Fe_(2)O_(3) pressure standard upon compression.The efficiency of pressure generation in the newly developed cell assembly equipped with conventional ZK10F WC anvils is significantly higher than that of conventional assemblies with some ultrahard or tapered WC anvils.Our study has enabled the routine gener-ation of pressures exceeding 50 GPa within a millimeter-sized sample chamber that have been inaccessible with traditional KLVPs.This advance in high-pressure technology not only breaks a record for pressure generation in traditional KLVPs,but also opens up new avenues for exploration of the properties of the Earth’s deep interior and for the synthesis of novel materials at extreme high pressures.
基金supported by the National Key R&D Program of China(Grant No.2023YFA1406200)the National Natural Science Foundation of China(NSFC)(Grant Nos.12174143 and 12404014)the Basic Science Center Project of the NSFC(Grant No.52388201).
文摘High pressure enables the creation of novel functional materials by modifying chemical bonding and crystal structure,opening avenues for the development of high-energy-density polynitrogen materials.We present the high-pressure synthesis of three polynitrides P1 AgN7,P21/c AgN5,and P-1 AgN4,achieved through direct reactions between silver and nitrogen.Notably,the synthesis pressures required for the formation of N5 and N6 rings from metal–nitrogen reactions in this work represent the lowest values reported to date in high-pressure studies.At 15 GPa,isolated N5 rings are stabilized in P1 AgN7 and P21/c AgN5.At 26.3 GPa,P-1 AgN4 is synthesized,featuring infinite onedimensional nitrogen chains composed of alternating N2 and N6 rings,a unique catenation not observed in other polynitrides.In addition,AgN7,AgN5,and AgN4 possess significantly higher volumetric energy densities Ev than the conventional explosive TNT,making them promising high-energy-density materials.
基金supported by the National Key R&D Program of China(Gran Nos.2022YFA1402304 and 2022YFA1402802)the National Natural Science Foundation of China(Grant Nos.12494591,12122405,12274169,and 92165204)+4 种基金Program for Science and Technology Innovation Team in Zhejiang(Grant No.2021R01004)Guangdong Provincial Key Laboratory of Magnetoelectric Physics and Devices(Grant No.2022B1212010008)Guangdong Fundamental Research Center for Magnetoelectric Physics(2024B0303390001)Guangdong Provincial Quantum Science Strategic Initiative(Grant No.GDZX2401010)the Fundamental Research Funds for the Central Universities。
文摘The discovery of high-temperature superconductivity in bilayer nickelate La_(3)Ni_(2)O_(7)under high-pressure conditions has spurred extensive efforts to stabilize superconductivity at ambient pressure.Recently,the realization of superconductivity in compressively strained La_(3)Ni_(2)O_(7)thin films grown on the SrLaAlO_(4)substrates,with a T_(c)exceeding 40 K,represents a significant step toward this goal.Here,we investigate the influence of film thickness and carrier doping on the electronic structure of La_(3)Ni_(2)O_(7)thin films,ranging from 0.5 to 3 unit cells,using first-principles calculations.For a 2 unit-cell film with an optimal doping concentration of 0.3 hole per formula unit(0.15 hole/Ni),the Ni-d_(z^(2))interlayer bonding state crosses the Fermi level,resulting in the formation ofγpockets at the Fermi surface.These findings align with angle-resolved photoemission spectroscopy experimental data.Our results provide theoretical validation for the recent experimental discovery of ambient-pressure superconductivity in La_(3)Ni_(2)O_(7)thin films and underscore the significant impact of film thickness and carrier doping on electronic property modulation.
基金supported by the Jilin Province Science and Technology Development Program,China(Grant No.20250102013JC).
文摘Phase engineering has proven to be an effective strategy for achieving superior thermoelectric performance,while pressure is an excellent means of expanding the phase space of a material.In this paper,the effect of pressure-induced phase transition on improving the crystal symmetry and enhancing the thermoelectric properties of AgCrSe2 under high pressure and high temperature are reported.A structural phase transition from the low-symmetry R3m phase to the high-symmetry P3m1 phase is discovered below 1 GPa,which increases band degeneracy and contributes to a high electrical conductivity.For the metallic P3m1 phase,the electrons surrounding the Se2−anion gradually transfer to the Ag+and Cr3+cations as the pressure increases,decreasing the density of states around the Fermi level and thus optimizing the carrier concentration,thereby increasing the Seebeck coefficient while maintaining a high electrical conductivity.Consequently,an ultrahigh power factor of 864μW⋅m−1⋅K−2 is achieved at 5 GPa and 297 K.This study provides new insights into improving thermoelectric transport properties by applying physical pressure to enhance crystal symmetry and optimize thermoelectric parameters,and also indicates that phase engineering is a compelling strategy to discover or design novel high-performance thermoelectric materials starting from low-symmetry compounds.
基金support from the Program for the Development of Science and Technology of Jilin Province(Grant No.SKL202402004)the Jilin Province Major Science and Technology Program(Grant No.20240211002GX)the Open Research Fund of the Key Laboratory of Functional Materials Physics and Chem-istry of the Ministry of Education(Jilin Normal University,Grant No.202405).
文摘Continuously improving the mechanical properties of ultra-high-temperature ceramics(UHTCs)is a key requirement for their future applications.However,the mechanical properties of conventional UHTCs,HfB_(2) and ZrB_(2),remain unsatisfactory among transition metal light-element(TMLE)compounds.TiB_(2) has superior mechanical properties compared to both HfB_(2) and ZrB_(2),but suffers from inherent brittleness and limited oxidation resistance.In this work,low-content solidsolution strengthening was used to fabricate dense samples of Tix(Hf/Zr)_(1-x)B_(2)(THZ)under high pressure and high temperature(HPHT).Compared to pure TiB_(2),Ti_(0.94)(Hf/Zr)0.06B_(2) exhibits a significant 38.8%increase in oxidation resistance temperature(950℃),while Ti_(0.91)(Hf/Zr)_(0.09)B_(2) shows a notable 28%enhancement in fracture toughness(5.8 MPa·m^(1/2)).The synergistic effect of a dual-atom solid-solution results in local internal stress and anomalous lattice contraction.This lattice contraction helps resist oxygen invasion,thereby elevating the oxidation resistance threshold.Additionally,the internal stress induces crack deflection within individual grains,enhancing toughness through energy dissipation.This work provides a new strategy for fabricating robust UHTCs within TMLE systems,demonstrating significant potential for future high-temperature applications.
基金Project supported by the National Key R&D Program of China(Grant Nos.2022YFA1402503,2023YFA1406200,2023YFB3003001)the National Natural Science Foundation of China(Grant Nos.12074138 and 12047530)+2 种基金the Interdisciplinary Integration and Innovation Project of JLUFundamental Research Funds for the Central Universitiesthe Program for JLU Science and Technology Innovative Research Team(JLUSTIRT)。
文摘High-mobility semiconductor nanotubes have demonstrated great potential for applications in high-speed transistors,single-charge detection,and memory devices.Here we systematically investigated the electronic properties of single-walled boron antimonide(BSb)nanotubes using first-principles calculations.We observed that rolling the hexagonal boron antimonide monolayer into armchair(ANT)and zigzag(ZNT)nanotubes induces compression and wrinkling effects,significantly modifying the band structures and carrier mobilities through band folding andπ^(*)-σ^(*)hybridization.As the chiral index increases,the band gap and carrier mobility of ANTs decrease monotonically,where electron mobility consistently exceeds hole mobility.In contrast,ZNTs exhibit a more complex trend:the band gap first increases and then decreases,and the carrier mobility displays oscillatory behavior.In particular,both ANTs and ZNTs could exhibit significantly higher carrier mobilities compared to hexagonal monolayer and zinc-blende BSb,reaching 10^(-3)-10^(-7) cm^(-2)·V^(-1)·s^(-1).Our findings highlight strong curvature-induced modifications in the electronic properties of single-walled BSb nanotubes,demonstrating the latter as a promising candidate for high-performance electronic devices.
基金the National Natural Science Foundation of China(12274170 and 52225203)。
文摘Lonsdaleite,also known as hexagonal diamond,is an allotrope of carbon with a hexagonal crystal structure,which was discovered in the nanostructure of the Canyon Diablo meteorite.Theoretical calculations have shown that this structure gives it exceptional physical properties that exceed those of cubic diamond,making it highly promising for groundbreaking applications in superhard cutting tools,wide-bandgap semiconductor devices,and materials for extreme environments.As a result,the controllable synthesis of hexagonal diamond has emerged as a cutting-edge research focus in materials science.This review briefly outlines the progress in this area,with a focus on the mechanisms governing its key synthesis conditions,its intrinsic physical properties,and its potential applications in various fields.
基金supported by the National Key R&D Program of China (Grant No.2022YFA1405500)the National Natural Science Foundation of China (Grant No.52372257)。
文摘Ternary hydrides, with their superior chemical and structural flexibility over binary systems, open up new avenues for advancing high-performance superconductor research. The Y-Ca-H system is a promising candidate for high-temperature superconductors, as both Im3m YH_(6) and Im3m CaH_(6) exhibit similar structures and excellent superconducting properties, while Y and Ca atoms possess close atomic radii and electronegativities.Here, we report the successful synthesis of Im3m(Y, Ca)H_(6) achieving a maximum superconducting transition temperature(T_(c)) approximately 224 K at 155 GPa through five independent high-temperature and high-pressure experiments. Remarkably, the T_(c) of Im3m(Y, Ca)H_(6) remains highly stable(ΔT_(c) ≤ 1 K) during decompression between 148 and 165 GPa, significantly outperforming binary Im3m CaH_(6) and Im3m YH_(6). The enhanced superconducting properties may stem from the cooperative chemical template effect of Y and Ca atoms near the s-d border, which significantly reinforces H lattice stability and thus maintains superior superconductivity.This study highlights the potential of multicomponent cooperative effects in designing hydride superconductors,offering new insights for achieving high-T_(c) hydrides at lower pressures in the future.
基金supported by the National Key R&D Program of China(Grant No.2023YFA1406200)the National Natural Science Foundation of China(Grant Nos.12374004 and 12174141)the High Performance Computing Center of Jilin University,China。
文摘The discovery of pressure-induced superconducting electrides has sparked a intense wave of interest in novel superconductors.However,opinions vary regarding the relationship between non-nuclear attractors(NNAs)and superconductivity,with two opposing views currently represented by the materials Li_(6)P and Li_(6)C.Here,we choose the ternary Li–C–P as a model system and reveal the underlying mechanism by which NNAs contribute to superconductivity.The loosely bound NNAs in the superlithide Li_(14)CP covalently bond with Li and form unique satellite interstitial electrons(SIEs)around Li near the Fermi level,dominating the superconductivity.First-principles calculations show that the SIEs progressively increase in number and couple strongly with phonons at high pressure.Moreover,the Fermi surface nesting associated with SIEs induces phonon softening,further enhancing the electron–phonon coupling and giving the superlithide Li_(14)CP a T_(c)of 10.6 K at 300 GPa.The leading role of SIEs in superconductivity is a general one and is also relevant to the recently predicted Li_(6)P and Li_(6)C.Our work presented here reshapes the understanding of NNA-dominated superconductivity and holds promise for guiding future discoveries and designs of novel high-temperature superconductors.
基金support from the Science and Technology Development Project of Jilin Province(Grant No.SKL202402004)the Program for the Development of Science and Technology of Jilin Province(Grant No.YDZJ202201ZYTS308)the Open Research Fund of State Key Laboratory of Inorganic Synthesis and Preparative Chemistry(Jilin University,Grant Nos.2022-16 and 2022-23).
文摘Electrically conductive carbide ceramics with high hardness and fracture toughness are promising for advanced applications.However,enhancing both electrical conductivity and fracture toughness simultaneous is challenging.This study reports the synthesis of(Ti_(0.2)W_(0.2)Ta_(0.2)Hf_(0.2)Mo_(0.2))C-diamond composites with varying densities using high-pressure and high-temperature(HPHT)method.The carbides are uniformly dispersed in a titanium carbide matrix,forming conductive channels that reduce resistivity to 4.6×10^(-7)W·m.These composite materials exhibit metallic conductivity with a superconducting transition at 8.5 K.Superconducting behavior may result from d-p orbital hybridization and electron-phonon coupling in transition metal carbides,such as TaC,Mo_(2)C,and MoC.Optimizing intergranular bonding improves the fracture toughness without compromising hardness.The highest indentation toughness value is 10.1±0.4 MPa·m^(1/2),a 130%increase compare to pure TiC.Enhanced toughness arises from transgranular and intergranular fracture modes,multiple crack bridging,and large-angle crack deflection,which dissipate fracture energy and inhibit crack propagation.This study introduces a novel microstructure engineering strategy for carbide ceramics to achieve superior mechanical and electrical properties.
基金funding support from the National Science Fund for Distinguished Young Scholars(Grant No.T2225027)the National Natural Science Foundation of China(Grant Nos.12074013 and 12204419)the China Postdoctoral Science Foundation(Grant No.2021M702956)。
文摘Electrides,characterized by spatially confined anionic electrons,have emerged as a promising class of materials for catalysis,magnetism,and superconductivity.However,transition-metal-based electrides with diverse electron dimensionalities remain largely unexplored.Here,we perform a comprehensive first-principles investigation of Y-Co electrides,focusing on Y_(3)Co,Y_(3)Co_(2),and YCo.Our calculations reveal a striking dimensional evolution of anionic electrons:from two-dimensional(2D)confinement in YCo to one-dimensional(1D)in Y_(3)Co_(2)and zero-dimensional(0D)in Y_(3)Co.Remarkably,the YCo monolayer exhibits intrinsic ferromagnetism,with a magnetic moment of 0.65μB per formula unit arising from spin-polarized anionic electrons mediating long-range coupling between Y and Co ions.The monolayer also shows a low exfoliation energy(1.66 J/m^(2)),indicating experimental feasibility.All three electrides exhibit low work functions(2.76 eV-3.11 eV)along with Co-centered anionic states.This work expands the family of transition-metal-based electrides and highlights dimensionality engineering as a powerful strategy for tuning electronic and magnetic properties.
基金supported by the Natural Science Foundation of China(Grant Nos.T2325013,52288102,52090024,12034009,12474004,and 12304036)the National Key R&D Program of China Grant No.2023YFA1610000+1 种基金the Fundamental Research Funds for the Central Universitiesthe Program for Jilin University and Sun Yat-sen University.
文摘We report first-principles predictions of a cage-like polymeric nitrogen phase(cage-N)composed of interlocked N10 clusters stabilized by mixed sp^(2)/sp^(3) hybridization.Under high pressure,cage-N exhibits exceptional mechanical performance,including an ideal compressive strength of 343 GPa at a pressure of 300 GPa,~33% higher than that of diamond.This ultrahigh strength arises from the synergistic interplay between its three-dimensional covalent framework and hybridized bonding topology,which enables isotropic stress accommodation and dynamic electronic rearrangement.These results establish cage-N as a promising non-carbon ultrahard material and provide a bonding-driven route toward designing superhard frameworks under extreme conditions.
基金supported by the National Key R&D Program of China(grant nos.2022YFA1402300,2023YFA1406200,and 2019YFA0708502)the National Science Foundation of China(grant nos.22131006,12174144,12474009,22022101,and 22090041).
文摘The chemical synthesis of functional materials is inseparable from national defense,medical treatment,national economy,and people’s livelihood.Traditional organic and inorganic materials are approaching their performance limit.Therefore,the design and exploitation of novel functional materials are imminent and of significance for sustainable development.This review outlines the current progress and future prospects of chemical synthesis driven by high pressure,including organic and inorganic synthesis,as well as high-pressure phase retention.Based on the latest works,the basic mechanism of high-pressure chemical synthesis and three potential strategies for high-pressure phase harvesting are revealed.Finally,the challenge and outlook of high-pressureguided chemical synthesis are summarized.We sincerely hope that this review will provide guidance for designing high-performance materials by expanding the paths of chemical synthesis,thus greatly exploiting the existing materials world with newly emerging and enhanced functionalities.
基金supported by the National Key Research and Devel-opment Program of China(Grant Nos.2023YFA1406002 and 2023YFA1608901)the National Natural Science Foundation of China(Grant Nos.52288102,52090024,12374009,and T2495231)the Fundamental Research Funds for the Central Universities(Grant No.G1323525012).
文摘Conventional hard and superhard materials,such as diamond and cubic boron nitride,are attractive for both scientific and industrial applications,but their intrinsically poor electrical conductivity limits broader use.This motivates the exploration of novel materials that combine superior hardness with excellent superconductivity.Herein,we performed a comprehensive structure search of the B–C system under pressures ranging from 0 to 100 GPa using machine-learning-potential(attention-coupled neural network,ACNN)based crystal structure prediction(CALYPSO).A stable BC 19 phase was identified at 50 GPa,featuring a diamond-like covalent framework with metallic character.Interestingly,BC 19 shows anisotropic superconductivity with an estimated superconducting critical temperature(T c)of 24 K at ambient pressure.Further analysis indicates that the high superconductivity of BC 19 originates from the strong coupling between theσelectrons and stretching vibrations of the covalent B–C framework.Additionally,BC 19 demonstrates superhard characteristics with a Vickers hardness of 76 GPa,exceeding that of cubic boron nitride.These results suggest that pressure-stabilized BC 19 represents a promising theoretical candidate for concurrent superconductivity and ultrahard mechanical performance.
基金supported by the National Key R&D Program of China(2018YFA0305900)the National Natural Science Foundation of China(U23A20561,12274383,21703004,and 52172240)+1 种基金Fundamental Research Funds for the Central Universities,Sun Yatsen University(23qnpy04)Open Project of State Key Laboratory of Superhard Materials,Jilin University(202403).
文摘Diamond has the strongest three-dimensional network structure and its cubic configuration is extremely stable under high pressure,thus limiting the experimental synthesis of diamond polymorphs.Hexagonal diamond,a typical polymorph of diamond,has attracted considerable attention in recent decades,yet synthesizing pure and large-sized hexagonal diamond remains technically challenging,preventing an accurate understanding of its properties and formation mechanism.Here,we report the direct synthesis of millimeter-sized,nearly pure hexagonal diamond from graphite under high-pressure and high-temperature conditions using our developed high-pressure technique in a multi-anvil press.The synthesized hexagonal diamond is highly oriented polycrystalline,exhibiting an ultrahard hardness(165±4 GPa)on(100)planes,which is∼50%harder than single-crystal cubic diamond.Structural characterizations and molecular dynamics simulations indicate that hexagonal diamond is formed through a martensitic transformation process whereby hexagonal graphite is transformed into hexagonal diamond by sliding and then direct bonding between graphite sheets.Furthermore,we show that the transformations from graphite to cubic or hexagonal diamonds are strongly temperature-pressure dependent.With this understanding,we further synthesized cubic/hexagonal diamond composites with unusual heterostructures at a lower pressure.This work not only established a fundamental framework for high-pressure phase transformations in graphite but also provided insight into the structural evolution of two-dimensional materials at high pressures and a potent strategy for exploring their new high-pressure phases.
