When preparing SiC/Mg composites,alloy elements play key roles in the nucleation and interfacial wetting.In this paper,effects of Al,Zn and Zr additions on the Mg/SiC interfacial bonding properties were investigated c...When preparing SiC/Mg composites,alloy elements play key roles in the nucleation and interfacial wetting.In this paper,effects of Al,Zn and Zr additions on the Mg/SiC interfacial bonding properties were investigated comprehensively via method of first-principle calculations.Mg(0001)/SiC(0001)interfaces with different terminations and stacking sequences were built and CⅡ-T CⅡtop interface has the largest work of adhesion(W_(ad)).Zn dopants can not improve the W_(ad)for both C-T and Si-T interfaces.Al atom can only strengthen the C-T interface.Zr addition can greatly improve the W_(ad)for both C-T and Si-T interfaces.W_(ad)of C-T interfaces can reach up to 11.55 J/m^(2) and 12.55 J/m^(2) after doping 1 monolayer(ML)of Al and Zr atoms.Larger W_(ad)can lead to lower contact angles of Mg on SiC surfaces,which can improve wetting and nucleation in SiC/Mg composites.Analysis of electronic structure shows that Al-C and Zr-C bonds have more covalent composition than the Mg-C bond,which is responsible for the improvement of interfacial bonding strength.Experimental results in references were also analyzed,which are in well agreement with our calculation results.展开更多
As a large family of 2D materials, transition metal dichalcogenides(TMDs) have stimulated numerous works owing to their attractive properties. The replacement of constituent elements could promote the discovery and fa...As a large family of 2D materials, transition metal dichalcogenides(TMDs) have stimulated numerous works owing to their attractive properties. The replacement of constituent elements could promote the discovery and fabrication of new nanofilm in this family. Using precious metals, such as platinum and palladium, to serve as transition metals combined with chalcogen is a new approach to explore novel TMDs. Also, the proportion between transition metal and chalcogen atoms is found not only to exist in conventional form of 1 : 2. Herein, we reported a comprehensive study of a new 2D precious metal selenide, namely AuSe monolayer. Based on density functional theory, our result indicated that AuSe monolayer is a semiconductor with indirect band-gap of 2.0 eV, which possesses superior dynamic stability and thermodynamic stability with cohesive energy up to–7.87 eV/atom. Moreover, it has been confirmed that ionic bonding predominates in Au–Se bonds and absorption peaks in all directions distribute in the deep ultraviolet region. In addition, both vibration modes dominating marked Raman peaks are parallel to the 2D plane.展开更多
To investigate the origin of the strong dependence of martensitic transformation temperature on composition, the elastic properties of high temperature B2 phases of both NiTi and NiAl were calculated by a first-princi...To investigate the origin of the strong dependence of martensitic transformation temperature on composition, the elastic properties of high temperature B2 phases of both NiTi and NiAl were calculated by a first-principle method, the exact-muffin orbital method within coherent potential approximation. In the composition range of 50–56 at. pct Ni of NiTi and 60–70 at. pct Ni of NiAl in which martensitic transformation occurs, non-basal- plane shear modulus c44 increases with increasing Ni content, while basal-plane shear modulus c' decreases. In the above composition ranges however the transformation temperature of NiAl increases with increasing Ni content while that of NiTi decreases from experimental observation. The softening of c' is experimentally observed only in NiAl, and the decrease of c with increasing Ni content is responsible for the increase of transformation temperature. The result of the present work demonstrates that, besides c' , c44 also influences the martensitic transformation of NiTi and plays quite important a role.展开更多
The electronic and structural properties for Ti3SiC2 were studied using the first-principle calculation method. By using the calculated band structure and density of states, the high electrical conductivity of Ti3SiC2...The electronic and structural properties for Ti3SiC2 were studied using the first-principle calculation method. By using the calculated band structure and density of states, the high electrical conductivity of Ti3SiC2 are explained. The bonding character of Ti3SiC2 is analyzed in the map of charge density distribution.展开更多
Controversies about the phase diagram for the isostructural γ ? α phase transition of cerium have long been standing out for several decades. To seek insight into the problems, high-precision equations of state(EOS)...Controversies about the phase diagram for the isostructural γ ? α phase transition of cerium have long been standing out for several decades. To seek insight into the problems, high-precision equations of state(EOS) for γ-and α-cerium are constructed based on first-principle calculation. Versus previous works, the strong anharmonic effects of ion vibration and the variation of magnetism of γ-cerium are stressed. The new EOS generally agrees well with experimental data regarding thermodynamics, phase diagrams, and phase transitions. However, new EOS predicts that another part of phase boundary in pressure-temperature space may exist except for the commonly known boundary. In addition, the well-known critical point seems to be a critical point for γ-cerium to translate from a stable state to an unstable state.展开更多
The interesting hybrid properties of ceramics and metals induced by unique nano-laminated structures make the M_(n+1)AX n(MAX)phase attractive as a potential protective coating for vital structural compo-nents in hars...The interesting hybrid properties of ceramics and metals induced by unique nano-laminated structures make the M_(n+1)AX n(MAX)phase attractive as a potential protective coating for vital structural compo-nents in harsh systems.However,an extremely narrow phase-forming region makes it difficult to prepare MAX phase coatings with high purity,which is required to obtain coatings with high-temperature anti-oxidation capabilities.This work describes the dependence of the phase evolution in deposited M-Al-C(M=Ti,V,Cr)coatings as a function on temperature using in-situ X-ray diffraction analysis.Compared to V_(2)AlC and Cr_(2)AlC MAX phase coatings,the Ti_(2)AlC coating displayed a higher phase-forming tempera-ture accompanied by a lack of any intermediate phases before the appearance of the Ti_(2)AlC MAX phase.The results of the first-principle calculations correlated with the experience in which Ti_(2)AlC exhibited the largest formation energy and density of states.The effect of the phase compositions of these three MAX phase coatings on mechanical properties were also investigated using ex-situ Vickers and nano-indenter tests,demonstrating the improved mechanical properties with good stability at high temperatures.These findings provide a deeper understanding of the phase-forming mechanism of MAX phase coatings to guide the preparation of high-purity MAX phase coatings and the optimization of MAX phase coatings with expected intermediate phases such as Cr_(2)C,V_(2)C etc.,as well as their application as protective coat-ings in temperature-related harsh environments.展开更多
The martensitic transformation,mechanical,and magnetic properties of the Ni_(2)Mn_(1.5-x)Cu_(x)Ti_(0.5) (x=0.125,0.25,0.375,0.5) and Ni_(2-y)Co_(y)Mn_(1.5-x)Cu_(x)Ti_(0.5)[(x=0.125,y=0.125,0.25,0.375,0.5) and (x=0.125...The martensitic transformation,mechanical,and magnetic properties of the Ni_(2)Mn_(1.5-x)Cu_(x)Ti_(0.5) (x=0.125,0.25,0.375,0.5) and Ni_(2-y)Co_(y)Mn_(1.5-x)Cu_(x)Ti_(0.5)[(x=0.125,y=0.125,0.25,0.375,0.5) and (x=0.125,0.25,0.375,y=0.625)]alloys were systematically studied by the first-principles calculations.For the formation energy,the martensite is smaller than the austenite,the Ni–(Co)–Mn–Cu–Ti alloys studied in this work can undergo martensitic transformation.The austenite and non-modulated (NM) martensite always present antiferromagnetic state in the Ni_(2)Mn_(1.5-x)Cu_(x)Ti_(0.5) and Ni_(2-y)Co_(y)Mn_(1.5-x)Cu_(x)Ti_(0.5) (y<0.625) alloys.When y=0.625 in the Ni_(2-y)Co_(y)Mn_(1.5-x)Cu_(x)Ti_(0.5) series,the austenite presents ferromagnetic state while the NM martensite shows antiferromagnetic state.Cu doping can decrease the thermal hysteresis and anisotropy of the Ni–(Co)–Mn–Ti alloy.Increasing Mn and decreasing Ti content can improve the shear resistance and normal stress resistance,but reduce the toughness in the Ni–Mn–Cu–Ti alloy.And the ductility of the Co–Cu co-doping alloy is inferior to that of the Ni–Mn–Cu–Ti and Ni–Co–Mn–Ti alloys.The electronic density of states was studied to reveal the essence of the mechanical and magnetic properties.展开更多
The initial micro-galvanic corrosion behavior of Mg-30wt%Ca alloy only containing Mg_(2)Ca andα-Mg was studied by immersion testing in a 0.9%Na Cl solution at 37°C.The quasi-in situ SEM and TEM results show that...The initial micro-galvanic corrosion behavior of Mg-30wt%Ca alloy only containing Mg_(2)Ca andα-Mg was studied by immersion testing in a 0.9%Na Cl solution at 37°C.The quasi-in situ SEM and TEM results show that Mg_(2)Ca corroded easier thanα-Mg,indicating that Mg_(2)Ca acted as an anode.The work function(Φ)for Mg_(2)Ca calculated by first-principles is significantly lower compared to that forα-Mg.The Volta potential measured by a scanning Kelvin probe force microscope reveals that the Mg_(2)Ca had a relatively low Volta potential(ψ)value.The lowerΦandψvalues for Mg_(2)Ca indicate a lower electrochemical nobility,which is consistent with the experimental phenomenon.展开更多
Fe/Co-based diatomic catalysts decorated on an N-doped graphene substrate are investigated by first-principles calculations to improve the electrochemical properties of Li–S batteries.Our results demonstrate that Fe ...Fe/Co-based diatomic catalysts decorated on an N-doped graphene substrate are investigated by first-principles calculations to improve the electrochemical properties of Li–S batteries.Our results demonstrate that Fe CoN8@Gra not only possesses moderate adsorption energies towards Li2Snspecies,but also exhibits superior catalytic activity for both reduction and oxidation reactions of the sulfur cathode.Moreover,the metallic property of the diatomic catalysts can be well maintained after Li2Snadsorption,which could help the sulfur cathode to maintain high conductivity during the whole charge–discharge process.Given these exceptional properties,it is expected that Fe CoN8@Gra could be a promising diatomic catalyst for Li–S batteries and afford insights for further development of advanced Li–S batteries.展开更多
Garnet-type Li_(7)La_(3)Zr_(2)O_(12)(LLZO) is a promising solid-state electrolyte for Li-ion batteries,but Li-dendrite's formation greatly limits the applications.In this paper,we systematically investigate the st...Garnet-type Li_(7)La_(3)Zr_(2)O_(12)(LLZO) is a promising solid-state electrolyte for Li-ion batteries,but Li-dendrite's formation greatly limits the applications.In this paper,we systematically investigate the stability,electronic properties,and Li-ion mobility of the LLZO surface by the ifrst-principles calculations.We consider the(110) and(001) slab structures with different terminations in the t-and c-LLZO.Our results indicate that both(110) and(001) surfaces prefer to form Li-rich termination due to their low surface energies for either t-or c-LLZO.Moreover,with the decrease of Li contents the stability of Li-rich surfaces is improved initially and degrades later.Unfortunately,the localized surface states at the Fermi level can induce the formation of metallic Li on the Li-rich surfaces.In comparison,Li/La-termination has a relatively low metallic Li formation tendency due to its rather low diffusion barrier.In fact,Li-ion can spontaneously migrate along path II(Li3→Li2) on the Li/La-T(001) surface.In contrast,it is more difficult for Li-ion diffusion on the Li-T(001) surface,which has a minimum diffusion barrier of 0.50 eV.Interestingly,the minimum diffusion barrier decreases to 0.34 eV when removing four Li-ions from the Li-T(001) surface.Thus,our study suggests that by varying Li contents,the stability and Li-ion diffusion barrier of LLZO surfaces can be altered favorably.These advantages can inhibit the formation of metallic Li on the LLZO surfaces.展开更多
SiO–based materials are promising alloys and conversion-type anode materials for lithium-ion batteries and are recently found to be excellent dendrite-proof layers for lithium-metal batteries.However,only a small fra...SiO–based materials are promising alloys and conversion-type anode materials for lithium-ion batteries and are recently found to be excellent dendrite-proof layers for lithium-metal batteries.However,only a small fraction of the Li–Si–O compositional space has been reported,significantly impeding the understanding of the phase transition mechanisms and the rational design of these materials both as anodes and as protection layers for lithium-metal anodes.Herein,we identify three new thermodynamically stable phases within the Li–Si–O ternary system(Li_(2)SiO_(5),Li_(4)SiO_(6),and Li_(4)SiO_(8))in addition to the existing records via first-principle calculations.The electronic structure simulation shows that Li_(2)SiO_(5)and Li_(4)SiO_(8)phases are metallic in nature,ensuring high electronic conductivity required as electrodes.Moduli calculations demonstrate that the mechanical strength of Li–Si–O phases is much higher than that of lithium metal.The diffusion barriers of interstitial Li range from 0.1 to 0.6 eV and the interstitial Li hopping serves as the dominating diffusion mechanism in the Li–Si–O ternary systems compared with vacancy diffusion.These findings provide a new strategy for future discovery of improved alloying anodes for lithium-ion batteries and offer important insight towards the understanding of the phase transformation mechanism of alloy-type protection layers on lithium-metal anodes.展开更多
The paper reports on the atomic investigation aboutβphase in Mg_(96)Gd_(2)Y_(1)Ni_(1) alloy by using the first-principles study and the high-angle annular dark-field scanning transmission electron microscope(HAADF-ST...The paper reports on the atomic investigation aboutβphase in Mg_(96)Gd_(2)Y_(1)Ni_(1) alloy by using the first-principles study and the high-angle annular dark-field scanning transmission electron microscope(HAADF-STEM)corrected by atomic Cs.By using HAADF-STEM,the rectangularβphases were observed in the underage and peak aging stages in Mg_(96)Gd_(2)Y_(1)Ni_(1) alloy.Theβphase could be precipitated from the previously precipitatedβphase,and theβphase grew in steps when it was precipitated.A special transition structure of three atomic layer thicknesses was first observed at the edge of theβphase and the structure of this interface is probably as theβ/Mg_(1) interface for the analysis of thermodynamic characterization and electronic characterization.Theβ'phase and theβ_(H) structure were precipitated only at the edge of the length directions of theβphase.Theβ'phase continues to grow into aβphase directly without the formation ofβ_(1) phase,resulting in an increase in the length of theβphase,which is discovered for the first time.展开更多
As a new generation electrode materials for energy storage,perovskites have attracted wide attention because of their unique crystal structure,reversible active sites,rich oxygen vacancies,and good stability.In this r...As a new generation electrode materials for energy storage,perovskites have attracted wide attention because of their unique crystal structure,reversible active sites,rich oxygen vacancies,and good stability.In this review,the design and engineering progress of perovskite materials for supercapacitors(SCs)in recent years is summarized.Specifically,the review will focus on four types of perovskites,perovskite oxides,halide perovskites,fluoride perovskites,and multi-perovskites,within the context of their intrinsic structure and corresponding electrochemical performance.A series of experimental variables,such as synthesis,crystal structure,and electrochemical reaction mechanism,will be carefully analyzed by combining various advanced characterization techniques and theoretical calculations.The applications of these materials as electrodes are then featured for various SCs.Finally,we look forward to the prospects and challenges of perovskite-type SCs electrodes,as well as the future research direction.展开更多
A versatile analytical method(VAM) for calculating the harmonic components of the magnetomotive force(MMF) generated by diverse armature windings in AC machines has been proposed, and the versatility of this method ha...A versatile analytical method(VAM) for calculating the harmonic components of the magnetomotive force(MMF) generated by diverse armature windings in AC machines has been proposed, and the versatility of this method has been established in early literature. However, its practical applications and significance in advancing the analysis of AC machines need further elaboration. This paper aims to complement VAM by augmenting its theory, offering additional insights into its conclusions, as well as demonstrating its utility in assessing armature windings and its application of calculating torque for permanent magnet synchronous machines(PMSM). This work contributes to advancing the analysis of AC machines and underscores the potential for improved design and performance optimization.展开更多
Electrocatalytic water splitting is crucial for H2generation via hydrogen evolution reaction(HER)but subject to the sluggish dynamics of oxygen evolution reaction(OER).In this work,single Fe atomdoped MoS_(2)nanosheet...Electrocatalytic water splitting is crucial for H2generation via hydrogen evolution reaction(HER)but subject to the sluggish dynamics of oxygen evolution reaction(OER).In this work,single Fe atomdoped MoS_(2)nanosheets(SFe-DMNs)were prepared based on the high-throughput density functional theory(DFT)calculation screening.Due to the synergistic effect between Fe atom and MoS_(2)and optimized intermediate binding energy,the SFe-DMNs could deliver outstanding activity for both HER and OER.When assembled into a two-electrode electrolytic cell,the SFe-DMNs could achieve the current density of 50 mA cm^(-2)at a low cell voltage of 1.55 V under neutral condition.These results not only confirmed the effectiveness of high-throughput screening,but also revealed the excellent activity and thus the potential applications in fuel cells of SFe-DMNs.展开更多
Electronic structure and elastic properties of MgCu_(2),Mg_(2)Ca and MgZn_(2)phases were investigated by means of first-principles calculations from CASTEP program based on density functional theory(DFT).The calculate...Electronic structure and elastic properties of MgCu_(2),Mg_(2)Ca and MgZn_(2)phases were investigated by means of first-principles calculations from CASTEP program based on density functional theory(DFT).The calculated lattice parameters were in good agreement with the experimental and literature values.The calculated heats of formation and cohesive energies shown that MgCu_(2)has the strongest alloying ability and structural stability.The elastic constants of MgCu_(2),Mg_(2)Ca and MgZn_(2)phases were calculated,the bulk moduli,shear moduli,Young's moduli and Poisson's ratio were derived.The calculated results shown that MgCu_(2),Mg_(2)Ca and MgZn_(2)are all ductile phases.Among the three phases,MgCu_(2)has the strongest stiffness and the plasticity of MgZn_(2)phase is the best.The density of states(DOS),Mulliken electron occupation number and charge density difference of MgCu_(2),Mg_(2)Ca and MgZn_(2)phases were discussed to analyze the mechanism of structural stability and mechanical properties.展开更多
The structural, electronic, optical and thermodynamic properties of Mo_2Ga_2C are investigated using density functional theory(DFT) within the generalized gradient approximation(GGA). The optimized crystal structure i...The structural, electronic, optical and thermodynamic properties of Mo_2Ga_2C are investigated using density functional theory(DFT) within the generalized gradient approximation(GGA). The optimized crystal structure is obtained and the lattice parameters are compared with available experimental data. The electronic density of states(DOS) is calculated and analyzed. The metallic behavior for the compound is confirmed and the value of DOS at Fermi level is 4.2 states per unit cell per e V. Technologically important optical parameters(e.g., dielectric function, refractive index, absorption coefficient, photo conductivity, reflectivity, and loss function) are calculated for the first time. The study of dielectric constant(ε1) indicates the Drude-like behavior. The absorption and conductivity spectra suggest that the compound is metallic.The reflectance spectrum shows that this compound has the potential to be used as a solar reflector. The thermodynamic properties such as the temperature and pressure dependent bulk modulus, Debye temperature, specific heats, and thermal expansion coefficient of Mo_2Ga_2C MAX phase are derived from the quasi-harmonic Debye model with phononic effect also for the first time. Analysis of T c expression using available parameter values(DOS, Debye temperature, atomic mass,etc.) suggests that the compound is less likely to be superconductor.展开更多
To clarify the effect of pressure on a(TaNb)0.67(HfZrTi)0.33 alloy composed of a solid solution with a single body-centered-cubic crystal structure,we used first-principles calculations to theoretically investigate th...To clarify the effect of pressure on a(TaNb)0.67(HfZrTi)0.33 alloy composed of a solid solution with a single body-centered-cubic crystal structure,we used first-principles calculations to theoretically investigate the structural,elastic,and electronic properties of this alloy at different pressures.The results show that the calculated equilibrium lattice parameters are consistent with the experimental results,and that the normalized structural parameters of lattice constants and volume decrease whereas the total enthalpy differenceΔE and elastic constants increase with increasing pressure.The(TaNb)0.67(HfZrTi)0.33 alloy exhibits mechanical stability at high pressures lower than 400 GPa.At high pressure,the bulk modulus B shows larger values than the shear modulus G,and the alloy exhibits an obvious anisotropic feature at pressures ranging from 30 to 70 GPa.Our analysis of the electronic structures reveals that the atomic orbitals are occupied by the electrons change due to the compression of the crystal lattices under the effect of high pressure,which results in a decrease in the total density of states and a wider electron energy level.This factor is favorable for zero resistance.展开更多
The elastic, magnetoelastic, and phonon properties of Ni_2FeGa were investigated through first-principles calculations.The obtained elastic and phonon dispersion curves for the austenite and martensite phases agree we...The elastic, magnetoelastic, and phonon properties of Ni_2FeGa were investigated through first-principles calculations.The obtained elastic and phonon dispersion curves for the austenite and martensite phases agree well with available theoretical and experimental results. The isotropic elastic moduli are also predicted along with the polycrystalline aggregate properties including the bulk modulus, shear modulus, Young's modulus, and Poisson's ratio. The Pugh ratio indicates that Ni_2FeGa shows ductility, especially the austenite phase, which is consistent with the experimental results. The Debye temperatures of the Ni_2FeGa in the austenite and martensite phases are 344 K and 392 K, respectively. It is predicted that the magnetoelastic coefficient is -5.3 × 10~6 J/m^3 and magnetostriction coefficient is between 135 and 55 ppm in the Ni_2FeGa austenite phase.展开更多
Magnetism induced by the nonmagnetic dopants in the zinc-blende SiC (3C-SiC) is investigated by first-principle calculations. The atoms of the first 20 elements in the periodic table except inert gas are used to repla...Magnetism induced by the nonmagnetic dopants in the zinc-blende SiC (3C-SiC) is investigated by first-principle calculations. The atoms of the first 20 elements in the periodic table except inert gas are used to replace either Si or C atoms as dopants. We find that some nonmagnetic substitutional dopants (mainly the Group IA, Group IIA, Group IIIB, and Group VIIB elements) prefer the spin-polarized ground states with local magnetic moments. In general, the condition for obtaining the local magnetic moments and the magnetic ground state requires that the dopants are p-type and have large electronegativity difference from the neighboring host atoms. The magnetic moments can be tuned over a range between 1 μ B and 3 μ B by doping with the nonmagnetic elements. The nearest-neighbor exchange couplings J 0 between the local magnetic moments are quite large and the codoping method is proposed to increase the dopant concentration. These imply that the nonmagnetic doping in SiC may exhibit collective magnetism. Moreover, the Group IIA Mg and Ca atoms substituting the preferred Si atoms favor the ferromagnetic ground states with the half-metallic electronic properties, which suggests that Mg or Ca substitutional doping on the Si sites in SiC could be a potential route to fabricating the diluted magnetic semiconductors.展开更多
基金funded by China Postdoctoral Science Foundation(No.2020M670670)Foundation Strengthening Program(No:2019-JCJQ-00)+2 种基金Natural Science Foundation of Hebei Province(E2019202407)Science and Technology Research Project of Hebei Province Colleges and Universities(QN2019028)“Yuan Guang Scholar”Plan of Hebei University of Technology。
文摘When preparing SiC/Mg composites,alloy elements play key roles in the nucleation and interfacial wetting.In this paper,effects of Al,Zn and Zr additions on the Mg/SiC interfacial bonding properties were investigated comprehensively via method of first-principle calculations.Mg(0001)/SiC(0001)interfaces with different terminations and stacking sequences were built and CⅡ-T CⅡtop interface has the largest work of adhesion(W_(ad)).Zn dopants can not improve the W_(ad)for both C-T and Si-T interfaces.Al atom can only strengthen the C-T interface.Zr addition can greatly improve the W_(ad)for both C-T and Si-T interfaces.W_(ad)of C-T interfaces can reach up to 11.55 J/m^(2) and 12.55 J/m^(2) after doping 1 monolayer(ML)of Al and Zr atoms.Larger W_(ad)can lead to lower contact angles of Mg on SiC surfaces,which can improve wetting and nucleation in SiC/Mg composites.Analysis of electronic structure shows that Al-C and Zr-C bonds have more covalent composition than the Mg-C bond,which is responsible for the improvement of interfacial bonding strength.Experimental results in references were also analyzed,which are in well agreement with our calculation results.
基金financially supported by the Natural Science Foundation of Jiangsu Province(No.BK20180071)the Fundamental Research Funds for the Central Universities(No.30919011109)PAPD of Jiangsu Higher Education Institutions
文摘As a large family of 2D materials, transition metal dichalcogenides(TMDs) have stimulated numerous works owing to their attractive properties. The replacement of constituent elements could promote the discovery and fabrication of new nanofilm in this family. Using precious metals, such as platinum and palladium, to serve as transition metals combined with chalcogen is a new approach to explore novel TMDs. Also, the proportion between transition metal and chalcogen atoms is found not only to exist in conventional form of 1 : 2. Herein, we reported a comprehensive study of a new 2D precious metal selenide, namely AuSe monolayer. Based on density functional theory, our result indicated that AuSe monolayer is a semiconductor with indirect band-gap of 2.0 eV, which possesses superior dynamic stability and thermodynamic stability with cohesive energy up to–7.87 eV/atom. Moreover, it has been confirmed that ionic bonding predominates in Au–Se bonds and absorption peaks in all directions distribute in the deep ultraviolet region. In addition, both vibration modes dominating marked Raman peaks are parallel to the 2D plane.
基金Part of the calculations in this work was performed ona Shenteng 6800 supercomputer at CNIC, China.
文摘To investigate the origin of the strong dependence of martensitic transformation temperature on composition, the elastic properties of high temperature B2 phases of both NiTi and NiAl were calculated by a first-principle method, the exact-muffin orbital method within coherent potential approximation. In the composition range of 50–56 at. pct Ni of NiTi and 60–70 at. pct Ni of NiAl in which martensitic transformation occurs, non-basal- plane shear modulus c44 increases with increasing Ni content, while basal-plane shear modulus c' decreases. In the above composition ranges however the transformation temperature of NiAl increases with increasing Ni content while that of NiTi decreases from experimental observation. The softening of c' is experimentally observed only in NiAl, and the decrease of c with increasing Ni content is responsible for the increase of transformation temperature. The result of the present work demonstrates that, besides c' , c44 also influences the martensitic transformation of NiTi and plays quite important a role.
文摘The electronic and structural properties for Ti3SiC2 were studied using the first-principle calculation method. By using the calculated band structure and density of states, the high electrical conductivity of Ti3SiC2 are explained. The bonding character of Ti3SiC2 is analyzed in the map of charge density distribution.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11272293 and U1230201)the Defense Industrial Technology Development Program(Grant No.B1520132001)the Foundation of National Key Laboratory of Shock Wave and Detonation Physics of China(Grant No.9140C670301140C67283)
文摘Controversies about the phase diagram for the isostructural γ ? α phase transition of cerium have long been standing out for several decades. To seek insight into the problems, high-precision equations of state(EOS) for γ-and α-cerium are constructed based on first-principle calculation. Versus previous works, the strong anharmonic effects of ion vibration and the variation of magnetism of γ-cerium are stressed. The new EOS generally agrees well with experimental data regarding thermodynamics, phase diagrams, and phase transitions. However, new EOS predicts that another part of phase boundary in pressure-temperature space may exist except for the commonly known boundary. In addition, the well-known critical point seems to be a critical point for γ-cerium to translate from a stable state to an unstable state.
基金financially supported by the National Natural Science Foundation of China (Nos.52025014,52171090,52101109,U22A20111).
文摘The interesting hybrid properties of ceramics and metals induced by unique nano-laminated structures make the M_(n+1)AX n(MAX)phase attractive as a potential protective coating for vital structural compo-nents in harsh systems.However,an extremely narrow phase-forming region makes it difficult to prepare MAX phase coatings with high purity,which is required to obtain coatings with high-temperature anti-oxidation capabilities.This work describes the dependence of the phase evolution in deposited M-Al-C(M=Ti,V,Cr)coatings as a function on temperature using in-situ X-ray diffraction analysis.Compared to V_(2)AlC and Cr_(2)AlC MAX phase coatings,the Ti_(2)AlC coating displayed a higher phase-forming tempera-ture accompanied by a lack of any intermediate phases before the appearance of the Ti_(2)AlC MAX phase.The results of the first-principle calculations correlated with the experience in which Ti_(2)AlC exhibited the largest formation energy and density of states.The effect of the phase compositions of these three MAX phase coatings on mechanical properties were also investigated using ex-situ Vickers and nano-indenter tests,demonstrating the improved mechanical properties with good stability at high temperatures.These findings provide a deeper understanding of the phase-forming mechanism of MAX phase coatings to guide the preparation of high-purity MAX phase coatings and the optimization of MAX phase coatings with expected intermediate phases such as Cr_(2)C,V_(2)C etc.,as well as their application as protective coat-ings in temperature-related harsh environments.
基金financially supported by the National Natural Science Foundation of China(No.51771044)the Natural Science Foundation of Hebei Province(No.E2019501061)+3 种基金the Performance subsidy fund for Key Laboratory of Dielectric and Electrolyte Functional Material Hebei Province(No.22567627H)the Fundamental Research Funds for the Central Universities(No.N2223025)the State Key Lab of Advanced Metals and Materials(No.2022-Z02)Programme of Introducing Talents of Discipline Innovation to Universities 2.0(the 111 Project of China 2.0,No.BP0719037)。
文摘The martensitic transformation,mechanical,and magnetic properties of the Ni_(2)Mn_(1.5-x)Cu_(x)Ti_(0.5) (x=0.125,0.25,0.375,0.5) and Ni_(2-y)Co_(y)Mn_(1.5-x)Cu_(x)Ti_(0.5)[(x=0.125,y=0.125,0.25,0.375,0.5) and (x=0.125,0.25,0.375,y=0.625)]alloys were systematically studied by the first-principles calculations.For the formation energy,the martensite is smaller than the austenite,the Ni–(Co)–Mn–Cu–Ti alloys studied in this work can undergo martensitic transformation.The austenite and non-modulated (NM) martensite always present antiferromagnetic state in the Ni_(2)Mn_(1.5-x)Cu_(x)Ti_(0.5) and Ni_(2-y)Co_(y)Mn_(1.5-x)Cu_(x)Ti_(0.5) (y<0.625) alloys.When y=0.625 in the Ni_(2-y)Co_(y)Mn_(1.5-x)Cu_(x)Ti_(0.5) series,the austenite presents ferromagnetic state while the NM martensite shows antiferromagnetic state.Cu doping can decrease the thermal hysteresis and anisotropy of the Ni–(Co)–Mn–Ti alloy.Increasing Mn and decreasing Ti content can improve the shear resistance and normal stress resistance,but reduce the toughness in the Ni–Mn–Cu–Ti alloy.And the ductility of the Co–Cu co-doping alloy is inferior to that of the Ni–Mn–Cu–Ti and Ni–Co–Mn–Ti alloys.The electronic density of states was studied to reveal the essence of the mechanical and magnetic properties.
基金funded by the National Key Research and Development Program of China(No.2017YFB0702504)
文摘The initial micro-galvanic corrosion behavior of Mg-30wt%Ca alloy only containing Mg_(2)Ca andα-Mg was studied by immersion testing in a 0.9%Na Cl solution at 37°C.The quasi-in situ SEM and TEM results show that Mg_(2)Ca corroded easier thanα-Mg,indicating that Mg_(2)Ca acted as an anode.The work function(Φ)for Mg_(2)Ca calculated by first-principles is significantly lower compared to that forα-Mg.The Volta potential measured by a scanning Kelvin probe force microscope reveals that the Mg_(2)Ca had a relatively low Volta potential(ψ)value.The lowerΦandψvalues for Mg_(2)Ca indicate a lower electrochemical nobility,which is consistent with the experimental phenomenon.
基金the National Natural Science Foundation of China(Grant Nos.51972140 and 51903164)the Fund from Science and Technology Department of Jilin Province,China(Grant No.20200201069JC).
文摘Fe/Co-based diatomic catalysts decorated on an N-doped graphene substrate are investigated by first-principles calculations to improve the electrochemical properties of Li–S batteries.Our results demonstrate that Fe CoN8@Gra not only possesses moderate adsorption energies towards Li2Snspecies,but also exhibits superior catalytic activity for both reduction and oxidation reactions of the sulfur cathode.Moreover,the metallic property of the diatomic catalysts can be well maintained after Li2Snadsorption,which could help the sulfur cathode to maintain high conductivity during the whole charge–discharge process.Given these exceptional properties,it is expected that Fe CoN8@Gra could be a promising diatomic catalyst for Li–S batteries and afford insights for further development of advanced Li–S batteries.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 12064015 and 12064014)。
文摘Garnet-type Li_(7)La_(3)Zr_(2)O_(12)(LLZO) is a promising solid-state electrolyte for Li-ion batteries,but Li-dendrite's formation greatly limits the applications.In this paper,we systematically investigate the stability,electronic properties,and Li-ion mobility of the LLZO surface by the ifrst-principles calculations.We consider the(110) and(001) slab structures with different terminations in the t-and c-LLZO.Our results indicate that both(110) and(001) surfaces prefer to form Li-rich termination due to their low surface energies for either t-or c-LLZO.Moreover,with the decrease of Li contents the stability of Li-rich surfaces is improved initially and degrades later.Unfortunately,the localized surface states at the Fermi level can induce the formation of metallic Li on the Li-rich surfaces.In comparison,Li/La-termination has a relatively low metallic Li formation tendency due to its rather low diffusion barrier.In fact,Li-ion can spontaneously migrate along path II(Li3→Li2) on the Li/La-T(001) surface.In contrast,it is more difficult for Li-ion diffusion on the Li-T(001) surface,which has a minimum diffusion barrier of 0.50 eV.Interestingly,the minimum diffusion barrier decreases to 0.34 eV when removing four Li-ions from the Li-T(001) surface.Thus,our study suggests that by varying Li contents,the stability and Li-ion diffusion barrier of LLZO surfaces can be altered favorably.These advantages can inhibit the formation of metallic Li on the LLZO surfaces.
基金supported by the Beijing Natural Science Foundation(2192029)the National Key Research and Development Program of China(2017YFB0702100)+6 种基金the National Natural Science Foundation of China(11404017,12004145)the Technology Foundation for Selected Overseas Chinese Scholarsthe Ministry of Human Resources and Social Security of Chinasupported by the Academic Excellence Foundation of BUAA for PhD Studentssupported by the Faraday Institution(grant number FIRG017)supported by the Singapore National Research Foundation(NRF-NRFF2017-04)supported by Jiangxi Provincial Natural Science Foundation(20212BAB214032)。
文摘SiO–based materials are promising alloys and conversion-type anode materials for lithium-ion batteries and are recently found to be excellent dendrite-proof layers for lithium-metal batteries.However,only a small fraction of the Li–Si–O compositional space has been reported,significantly impeding the understanding of the phase transition mechanisms and the rational design of these materials both as anodes and as protection layers for lithium-metal anodes.Herein,we identify three new thermodynamically stable phases within the Li–Si–O ternary system(Li_(2)SiO_(5),Li_(4)SiO_(6),and Li_(4)SiO_(8))in addition to the existing records via first-principle calculations.The electronic structure simulation shows that Li_(2)SiO_(5)and Li_(4)SiO_(8)phases are metallic in nature,ensuring high electronic conductivity required as electrodes.Moduli calculations demonstrate that the mechanical strength of Li–Si–O phases is much higher than that of lithium metal.The diffusion barriers of interstitial Li range from 0.1 to 0.6 eV and the interstitial Li hopping serves as the dominating diffusion mechanism in the Li–Si–O ternary systems compared with vacancy diffusion.These findings provide a new strategy for future discovery of improved alloying anodes for lithium-ion batteries and offer important insight towards the understanding of the phase transformation mechanism of alloy-type protection layers on lithium-metal anodes.
基金financially supported by the National Natural Science Foundation of China(Grant No.51825101)the National Key Research and Development Program of China(Grant No.2016YFB0701201)。
文摘The paper reports on the atomic investigation aboutβphase in Mg_(96)Gd_(2)Y_(1)Ni_(1) alloy by using the first-principles study and the high-angle annular dark-field scanning transmission electron microscope(HAADF-STEM)corrected by atomic Cs.By using HAADF-STEM,the rectangularβphases were observed in the underage and peak aging stages in Mg_(96)Gd_(2)Y_(1)Ni_(1) alloy.Theβphase could be precipitated from the previously precipitatedβphase,and theβphase grew in steps when it was precipitated.A special transition structure of three atomic layer thicknesses was first observed at the edge of theβphase and the structure of this interface is probably as theβ/Mg_(1) interface for the analysis of thermodynamic characterization and electronic characterization.Theβ'phase and theβ_(H) structure were precipitated only at the edge of the length directions of theβphase.Theβ'phase continues to grow into aβphase directly without the formation ofβ_(1) phase,resulting in an increase in the length of theβphase,which is discovered for the first time.
基金financial support from the National Natural Science Foundation of China(21676036)the Natural Science Foundation of Chongqing(CSTB2023NSCQ-MSX0580)the Graduate Research and Innovation Foundation of Chongqing(CYS-20040)。
文摘As a new generation electrode materials for energy storage,perovskites have attracted wide attention because of their unique crystal structure,reversible active sites,rich oxygen vacancies,and good stability.In this review,the design and engineering progress of perovskite materials for supercapacitors(SCs)in recent years is summarized.Specifically,the review will focus on four types of perovskites,perovskite oxides,halide perovskites,fluoride perovskites,and multi-perovskites,within the context of their intrinsic structure and corresponding electrochemical performance.A series of experimental variables,such as synthesis,crystal structure,and electrochemical reaction mechanism,will be carefully analyzed by combining various advanced characterization techniques and theoretical calculations.The applications of these materials as electrodes are then featured for various SCs.Finally,we look forward to the prospects and challenges of perovskite-type SCs electrodes,as well as the future research direction.
基金supported by the Natural Science Foundation of China under Grant U22A20214 and Grant 51837010。
文摘A versatile analytical method(VAM) for calculating the harmonic components of the magnetomotive force(MMF) generated by diverse armature windings in AC machines has been proposed, and the versatility of this method has been established in early literature. However, its practical applications and significance in advancing the analysis of AC machines need further elaboration. This paper aims to complement VAM by augmenting its theory, offering additional insights into its conclusions, as well as demonstrating its utility in assessing armature windings and its application of calculating torque for permanent magnet synchronous machines(PMSM). This work contributes to advancing the analysis of AC machines and underscores the potential for improved design and performance optimization.
基金supported by the Research Funds of Institute of Zhejiang University-Quzhou(IZQ2023RCZX032)the Natural Science Foundation of Guangdong Province(2022A1515010185)+1 种基金the Fundamental Research Funds for the Central Universities(FRF-TP-20-005A3)partially supported by the Special Funds for Postdoctoral Research at Tsinghua University(100415017)。
文摘Electrocatalytic water splitting is crucial for H2generation via hydrogen evolution reaction(HER)but subject to the sluggish dynamics of oxygen evolution reaction(OER).In this work,single Fe atomdoped MoS_(2)nanosheets(SFe-DMNs)were prepared based on the high-throughput density functional theory(DFT)calculation screening.Due to the synergistic effect between Fe atom and MoS_(2)and optimized intermediate binding energy,the SFe-DMNs could deliver outstanding activity for both HER and OER.When assembled into a two-electrode electrolytic cell,the SFe-DMNs could achieve the current density of 50 mA cm^(-2)at a low cell voltage of 1.55 V under neutral condition.These results not only confirmed the effectiveness of high-throughput screening,but also revealed the excellent activity and thus the potential applications in fuel cells of SFe-DMNs.
基金This work is supported by National Key Technology Research and Development Program of Ministry of Science and Technology of China(2011BAE22B00)Program for Liaoning Innovative Research Team in University.
文摘Electronic structure and elastic properties of MgCu_(2),Mg_(2)Ca and MgZn_(2)phases were investigated by means of first-principles calculations from CASTEP program based on density functional theory(DFT).The calculated lattice parameters were in good agreement with the experimental and literature values.The calculated heats of formation and cohesive energies shown that MgCu_(2)has the strongest alloying ability and structural stability.The elastic constants of MgCu_(2),Mg_(2)Ca and MgZn_(2)phases were calculated,the bulk moduli,shear moduli,Young's moduli and Poisson's ratio were derived.The calculated results shown that MgCu_(2),Mg_(2)Ca and MgZn_(2)are all ductile phases.Among the three phases,MgCu_(2)has the strongest stiffness and the plasticity of MgZn_(2)phase is the best.The density of states(DOS),Mulliken electron occupation number and charge density difference of MgCu_(2),Mg_(2)Ca and MgZn_(2)phases were discussed to analyze the mechanism of structural stability and mechanical properties.
文摘The structural, electronic, optical and thermodynamic properties of Mo_2Ga_2C are investigated using density functional theory(DFT) within the generalized gradient approximation(GGA). The optimized crystal structure is obtained and the lattice parameters are compared with available experimental data. The electronic density of states(DOS) is calculated and analyzed. The metallic behavior for the compound is confirmed and the value of DOS at Fermi level is 4.2 states per unit cell per e V. Technologically important optical parameters(e.g., dielectric function, refractive index, absorption coefficient, photo conductivity, reflectivity, and loss function) are calculated for the first time. The study of dielectric constant(ε1) indicates the Drude-like behavior. The absorption and conductivity spectra suggest that the compound is metallic.The reflectance spectrum shows that this compound has the potential to be used as a solar reflector. The thermodynamic properties such as the temperature and pressure dependent bulk modulus, Debye temperature, specific heats, and thermal expansion coefficient of Mo_2Ga_2C MAX phase are derived from the quasi-harmonic Debye model with phononic effect also for the first time. Analysis of T c expression using available parameter values(DOS, Debye temperature, atomic mass,etc.) suggests that the compound is less likely to be superconductor.
基金the National Natural Science Foundation of China(No.51701128)the Scientific Research Project of Education Department of Liaoning Province,China(No.JYT19037).
文摘To clarify the effect of pressure on a(TaNb)0.67(HfZrTi)0.33 alloy composed of a solid solution with a single body-centered-cubic crystal structure,we used first-principles calculations to theoretically investigate the structural,elastic,and electronic properties of this alloy at different pressures.The results show that the calculated equilibrium lattice parameters are consistent with the experimental results,and that the normalized structural parameters of lattice constants and volume decrease whereas the total enthalpy differenceΔE and elastic constants increase with increasing pressure.The(TaNb)0.67(HfZrTi)0.33 alloy exhibits mechanical stability at high pressures lower than 400 GPa.At high pressure,the bulk modulus B shows larger values than the shear modulus G,and the alloy exhibits an obvious anisotropic feature at pressures ranging from 30 to 70 GPa.Our analysis of the electronic structures reveals that the atomic orbitals are occupied by the electrons change due to the compression of the crystal lattices under the effect of high pressure,which results in a decrease in the total density of states and a wider electron energy level.This factor is favorable for zero resistance.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11174030 and 11504020)the Fundamental Research Funds for the Central Universities of China(Grant No.FRF-TP-16-064A1,06500031)
文摘The elastic, magnetoelastic, and phonon properties of Ni_2FeGa were investigated through first-principles calculations.The obtained elastic and phonon dispersion curves for the austenite and martensite phases agree well with available theoretical and experimental results. The isotropic elastic moduli are also predicted along with the polycrystalline aggregate properties including the bulk modulus, shear modulus, Young's modulus, and Poisson's ratio. The Pugh ratio indicates that Ni_2FeGa shows ductility, especially the austenite phase, which is consistent with the experimental results. The Debye temperatures of the Ni_2FeGa in the austenite and martensite phases are 344 K and 392 K, respectively. It is predicted that the magnetoelastic coefficient is -5.3 × 10~6 J/m^3 and magnetostriction coefficient is between 135 and 55 ppm in the Ni_2FeGa austenite phase.
基金Supported by the National Natural Science Foundation of China (Grant Nos.10674076 and 10721404)the Major Project of National Basic Research Program of China (Grant No. 2006CB605105)
文摘Magnetism induced by the nonmagnetic dopants in the zinc-blende SiC (3C-SiC) is investigated by first-principle calculations. The atoms of the first 20 elements in the periodic table except inert gas are used to replace either Si or C atoms as dopants. We find that some nonmagnetic substitutional dopants (mainly the Group IA, Group IIA, Group IIIB, and Group VIIB elements) prefer the spin-polarized ground states with local magnetic moments. In general, the condition for obtaining the local magnetic moments and the magnetic ground state requires that the dopants are p-type and have large electronegativity difference from the neighboring host atoms. The magnetic moments can be tuned over a range between 1 μ B and 3 μ B by doping with the nonmagnetic elements. The nearest-neighbor exchange couplings J 0 between the local magnetic moments are quite large and the codoping method is proposed to increase the dopant concentration. These imply that the nonmagnetic doping in SiC may exhibit collective magnetism. Moreover, the Group IIA Mg and Ca atoms substituting the preferred Si atoms favor the ferromagnetic ground states with the half-metallic electronic properties, which suggests that Mg or Ca substitutional doping on the Si sites in SiC could be a potential route to fabricating the diluted magnetic semiconductors.
