High-pressure structural phase transitions in PbTe are investigated by means of the first principles total energy calculations within the generalized gradient approximation (GOAl and local density approximation CLDA...High-pressure structural phase transitions in PbTe are investigated by means of the first principles total energy calculations within the generalized gradient approximation (GOAl and local density approximation CLDA) by using the density functional theory. First principle calculation shows that PbTe is stable with the NaCl-type (B1) structure under amSient conditions and transforms to the CsCl-type (B2) structure under high pressure via an intermediate phase. Two candidate structures of the intermediate phase, namely Prima and Cmcm, are chosen for total energy calculations and discussed. It indicates that the intermediate phase adopts the Pnma structure rather than the Cmcm structure, and lattice parameters of the Pnma phase calculated by using OGA and LDA are in consistent with experimental results.展开更多
Geometric and electronic structures of three polymorphs of BiPO4(m MBIP, n MBIP and HBIP) have been investigated by the first-principles calculations. The results show that PO4 tetrahedron in n MBIP is distorted mos...Geometric and electronic structures of three polymorphs of BiPO4(m MBIP, n MBIP and HBIP) have been investigated by the first-principles calculations. The results show that PO4 tetrahedron in n MBIP is distorted most, and m MBIP possesses minimum effective mass of carriers in three polymorphs of BiPO4. Further, the leading role of inductive effect of dipole moment or effective mass of carries in the separation of electron-hole pairs is analyzed. Based on the fact that n MBIP has higher photocatalytic activity than m MBIP, it can be inferred that the inductive effect of dipole moment deriving from distorted PO4 tetrahedron is the dominant factor affecting the separation efficiency of carries. The calculated results represent that n MBIP has more appropriate redox potential and narrower band gap than others. These findings may provide meaningful guidance for further understanding on the relationship between unique crystal structure and photocatalytic activity of BiPO4.展开更多
Several rocksalt Sr4X3N (X = O, S, Se, and Te) are predicted to be potential half-metallic ferromagnets free of transition-metal and rare-earth elements by performing the first-principles calculations. Then their ma...Several rocksalt Sr4X3N (X = O, S, Se, and Te) are predicted to be potential half-metallic ferromagnets free of transition-metal and rare-earth elements by performing the first-principles calculations. Then their magnetic properties, such as the half metallicity and the crystal-cell magnetic moments are investigated. The Sr4X3N possibly have higher Curie temperatures and have more stable half metallicity than the Sr4X3C. Their crystal-cell magnetic moments are all 1.00 μB. The crystal-cell magnetic moments and the half metallicity arise mainly from the N ions. The main mechanism is the strong covalent interaction leading to the sp2 hybridized orbitals in the Sr4X3N. Then two Sr-5s and three N-2p electrons enter into three sp2 hybridized orbitals. Among these five electrons, four electrons are paired and one is unpaired, so there are three spin-up electrons and two spin-down electrons in these sp2 hybridized orbitals.展开更多
Impurity formation energy, electronic structure, and photocatalytic properties of C-, N-, or S-doped BiOCl are investigated by density-functional theory plus U calculations(DFT + U). Results show that the doping effec...Impurity formation energy, electronic structure, and photocatalytic properties of C-, N-, or S-doped BiOCl are investigated by density-functional theory plus U calculations(DFT + U). Results show that the doping effect of S is better than that of C or N on the tunable photocatalytic activities of BiOCl. At low concentration, S-doped BiOCl systems are the most stable under Bi-rich growth conditions because of their lower impurity-formation energy. Compared with the electronic structures of S-doped BiOCl, C-or N-doped BiOCl have relatively deeper impurity energy levels appearing in their band gap(except Bi_(36)O_(35)NCl_(36)), which may act as photogenerated carrier-recombination centers and reduce photocatalytic activity. At high concentration, S is substituted on the O lattice site system, whereas some S 3p states mix with the valence band; this mixture leads to an obvious band-gap decrease and continuum-state formation above the valence-band edge of BiOCl. Such activity is advantageous to photochemical catalysis response. Compared with pure Bi OCl and a low-concentration S-doped system, a high-concentration S-doped system shows an obvious redshift on the absorption edge and has better photocatalytic O_2 evolution performance.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
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
Cs and I can migrate through fuel-cladding interfaces and accelerate the cladding corrosion process induced by the fuel-cladding chemical interaction.Cr coating has emerged as an important candidate for mitigating thi...Cs and I can migrate through fuel-cladding interfaces and accelerate the cladding corrosion process induced by the fuel-cladding chemical interaction.Cr coating has emerged as an important candidate for mitigating this chemical interaction.In this study,first-principles calculations were employed to investigate the diffusion behavior of Cs and I in the Cr bulk and grain boundaries to reveal the microscopic interaction mitigation mechanisms at the fuel-cladding interface.The interaction between these two fission products and the Cr coating were studied systematically,and the Cs and I temperature-dependent diffusion coefficients in Cr were obtained using Bocquet’s oversized solute-atom model and Le Claire’s nine-frequency model,respectively.The results showed that the Cs and I migration barriers were significantly lower than that of Cr,and the Cs and I diffusion coefficients were more than three orders of magnitude larger than the Cr self-diffusion coefficient within the temperature range of Generation-IV fast reactors(below 1000 K),demonstrating the strong penetration ability of Cs and I.Furthermore,Cs and I are more likely to diffuse along the grain boundary because of the generally low migration barriers,indicating that the grain boundary serves as a fast diffusion channel for Cs and I.展开更多
This study delves into the charge transfer mechanism of boron (B)-doped 3C-SiC through first-principles investigations. We explore the effects of B doping on the electronic properties of 3C-SiC, focusing on a 12.5% im...This study delves into the charge transfer mechanism of boron (B)-doped 3C-SiC through first-principles investigations. We explore the effects of B doping on the electronic properties of 3C-SiC, focusing on a 12.5% impurity concentration. Our comprehensive analysis encompasses structural properties, electronic band structures, and charge density distributions. The optimized lattice constant and band gap energy of 3C-SiC were found to be 4.373 Å and 1.36 eV respectively, which is in agreement with previous research (Bui, 2012;Muchiri et al., 2018). Our results show that B doping narrows the band gap, enhances electrical conductivity, and influences charge transfer interactions. The charge density analysis reveals substantial interactions between B dopants and surrounding carbon atoms. This work not only enhances our understanding of the material’s electronic properties, but also highlights the importance of charge density analysis for characterizing charge transfer mechanisms and their implications in the 3C-SiC semiconductors.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
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
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 Mo2Ga2C are investigated using density func- tional theory (DFT) within the generalized gradient approximation (GGA). The optimized crystal struc...The structural, electronic, optical and thermodynamic properties of Mo2Ga2C are investigated using density func- tional 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 eV. 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 Mo2Ga2C MAX phase are derived from the quasi-harmonic Debye model with phononic effect also for the first time. Analysis of Tc 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
The physical characters and electrochemical properties of various phases in a Sn-Zn electrode, such as formation energy, plateau potential, specific capacity, as well as volume expansion, were calculated by the first-...The physical characters and electrochemical properties of various phases in a Sn-Zn electrode, such as formation energy, plateau potential, specific capacity, as well as volume expansion, were calculated by the first-principles plane-wave pseudo-potential method based on the den- sity functional theory. Sn-Zn films were also deposited on copper foils by an electroless plating technique. The actual composition and chemical characters were explored by scanning electron microscopy (SEM), X-ray diffraction (XRD), plasma atomic emission spectrometry (ICP), and constant current charge/discharge measurements (CC). The results show that separation phases with tin and zinc including a small quantity of Cu6Sn5 phase were obtained, the initial lithium insertion capacity of the Sn-Zn film was 661 mAh/g, and obvious potential pla- teaus of about 0.4 V and 0.7 V were displayed, which is in accordance with the results of theoretical calculations. The capacity of the Sn-Zn film decreased seriously with the increase of cycle number.展开更多
Using first-principles calculations, we systematically study the dissociations of 02 molecules on different ultrathin Pb(lll) films. According to our previous work revealing the molecular adsorption precursor states...Using first-principles calculations, we systematically study the dissociations of 02 molecules on different ultrathin Pb(lll) films. According to our previous work revealing the molecular adsorption precursor states for O2, we further explore why there are two nearly degenerate adsorption states on Pb(lll) ultrathin films, but no precursor adsorption states existing at all on Mg(0001) and Al(lll) surfaces. The reason is concluded to be the different surface electronic structures. For the O2 dissociation, we consider both the reaction channels from gas-like and molecularly adsorbed O2 molecules. We find that the energy barrier for O2 dissociation from the molecular adsorption precursor states is always smaller than that from O2 gas. The most energetically favorable dissociation process is found to be the same on different Pb(lll) fihns, and the energy barriers are found to be influenced by the quantum size effects of Pb(lll) films.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
First-principles calculations were performed to investigate the mechanical properties of ZnO nanowires and to study the doping and size effects. A series of strains were applied to ZnO nanowires in the axial direction...First-principles calculations were performed to investigate the mechanical properties of ZnO nanowires and to study the doping and size effects. A series of strains were applied to ZnO nanowires in the axial direction and the elastic moduli of ZnO nanowires were obtained from the energy versus strain curves. Pure and Mn-doped ZnO nanowires with three different diameters (1.14, 1.43, and 1.74 nm) were studied. It is found that the elastic moduli of the ZnO nanowires are 146.5, 146.6, and 143.9 GPa, respectively, which are slightly larger than that of the bulk (140.1 GPa), and they increase as the diameter decreases. The elastic moduli of the Mn-doped ZnO nanowires are 137.6, 141.8, and 141.0 GPa, which are slightly lower than those of the undoped ones by 6.1%, 3.3%, and 2.0%, respectively. The mechanisms of doping and size effect were discussed in terms of chemical bonding and geometry considerations.展开更多
Using first-principles calculations within density functional theory, we study the atomic structures and electronic properties of the perfect and defective (2VCu+ Incu) CulnGaSe2/CdS interfaces theoretically, espec...Using first-principles calculations within density functional theory, we study the atomic structures and electronic properties of the perfect and defective (2VCu+ Incu) CulnGaSe2/CdS interfaces theoretically, especially the interface states. We find that the local lattice structure of (2VCu+ InCu) interface is somewhat disorganized. By analyzing the local density of states projected on several atomic layers of the two interfaces models, we find that for the (2VCu+InCu) interface the interface states near the Fermi level in CulnGaSe2 and CdS band gap regions are mainly composed of interracial Se-4p, Cu-3d and S-3p orbitals, while for the perfect interface there are no clear interface states in the CulnGaSe2 region but only some interface states which are mainly composed of S-3p orbitals in the valance band of CdS region.展开更多
Heterostructures(HSs)have attracted significant attention because of their interlayer van der Waals interactions.The electronic structures and optical properties of stacked GaN-MoS2 HSs under strain have been explored...Heterostructures(HSs)have attracted significant attention because of their interlayer van der Waals interactions.The electronic structures and optical properties of stacked GaN-MoS2 HSs under strain have been explored in this work using density functional theory.The results indicate that the direct band gap(1.95 e V)of the Ga N-MoS2 HS is lower than the individual band gaps of both the GaN layer(3.48 e V)and the MoS2 layer(2.03 eV)based on HSE06 hybrid functional calculations.Specifically,the GaN-MoS2 HS is a typical type-II band HS semiconductor that provides an effective approach to enhance the charge separation efficiency for improved photocatalytic degradation activity and water splitting efficiency.Under tensile or compressive strain,the direct band gap of the GaN-MoS2 HS undergoes redshifts.Additionally,the GaN-MoS2 HS maintains its direct band gap semiconductor behavior even when the tensile or compressive strain reaches 5%or-5%.Therefore,the results reported above can be used to expand the application of Ga N-MoS2 HSs to photovoltaic cells and photocatalysts.展开更多
The geometry, electronic structure and magnetic property of the hexagonal A1N (h-AIN) sheet doped by 5d atoms (Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au and Hg) are investigated by first-principles calculations based on t...The geometry, electronic structure and magnetic property of the hexagonal A1N (h-AIN) sheet doped by 5d atoms (Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au and Hg) are investigated by first-principles calculations based on the density functional theory. The influence of symmetry and symmetry-breaking is also studied. There are two types of local symmetries of the doped systems: C3v and D3h. The symmetry will deviate from exact C3,, and D3h for some particular dopants after optimization. The total magnetic moments of the doped systems are 0/-tB for Lu, Ta and It; 1 ~B for Hf, W, Pt and Hg; 2gB for Re and Au; and 3/~B for Os and Al-vacancy. The total densities of state are presented, where impurity energy levels exist. The impurity energy levels and total magnetic moments can be explained by the splitting of 5d orbitals or molecular orbitals under different symmetries.展开更多
基金Supported by the National Natural Science Foundation of China under Grant No 11474280the Chinese Academy of Sciences under Grant Nos KJCX2-SW-N20 and KJCX2-SW-N03
文摘High-pressure structural phase transitions in PbTe are investigated by means of the first principles total energy calculations within the generalized gradient approximation (GOAl and local density approximation CLDA) by using the density functional theory. First principle calculation shows that PbTe is stable with the NaCl-type (B1) structure under amSient conditions and transforms to the CsCl-type (B2) structure under high pressure via an intermediate phase. Two candidate structures of the intermediate phase, namely Prima and Cmcm, are chosen for total energy calculations and discussed. It indicates that the intermediate phase adopts the Pnma structure rather than the Cmcm structure, and lattice parameters of the Pnma phase calculated by using OGA and LDA are in consistent with experimental results.
基金supported by the National Natural Science Foundation of China(51472081,51102150)the Development Funds of Hubei Collaborative Innovation Center(HBSKFMS2014003,HBSKFMS2014011)+1 种基金the Foundation for High-Level Talents(GCRC13014)the Students Research Fund of Hubei Collaborative Innovation Center(HBSDY201511)
文摘Geometric and electronic structures of three polymorphs of BiPO4(m MBIP, n MBIP and HBIP) have been investigated by the first-principles calculations. The results show that PO4 tetrahedron in n MBIP is distorted most, and m MBIP possesses minimum effective mass of carriers in three polymorphs of BiPO4. Further, the leading role of inductive effect of dipole moment or effective mass of carries in the separation of electron-hole pairs is analyzed. Based on the fact that n MBIP has higher photocatalytic activity than m MBIP, it can be inferred that the inductive effect of dipole moment deriving from distorted PO4 tetrahedron is the dominant factor affecting the separation efficiency of carries. The calculated results represent that n MBIP has more appropriate redox potential and narrower band gap than others. These findings may provide meaningful guidance for further understanding on the relationship between unique crystal structure and photocatalytic activity of BiPO4.
基金Project supported by Chongqing Natural Science Foundation,China (Grant Nos.CSCT2010BB4405 and CSTC2008BB4083)the Doctoral Foundation of Chongqing University of Posts and Telecommunications,China(Grant No.A2008-63)
文摘Several rocksalt Sr4X3N (X = O, S, Se, and Te) are predicted to be potential half-metallic ferromagnets free of transition-metal and rare-earth elements by performing the first-principles calculations. Then their magnetic properties, such as the half metallicity and the crystal-cell magnetic moments are investigated. The Sr4X3N possibly have higher Curie temperatures and have more stable half metallicity than the Sr4X3C. Their crystal-cell magnetic moments are all 1.00 μB. The crystal-cell magnetic moments and the half metallicity arise mainly from the N ions. The main mechanism is the strong covalent interaction leading to the sp2 hybridized orbitals in the Sr4X3N. Then two Sr-5s and three N-2p electrons enter into three sp2 hybridized orbitals. Among these five electrons, four electrons are paired and one is unpaired, so there are three spin-up electrons and two spin-down electrons in these sp2 hybridized orbitals.
基金This project was supported by the China Postdoctoral Science Foundation,Henan Postdoctoral Science Foundation,NCWU 2017 Annual Teaching Teacher Training Object ProjectKey Research Projects of Higher Education in Henan Province(18B150010)+1 种基金the Key Scientific Research Project of Henan Higher Education(No.17A520011)the Science and Technology Research Project of Henan Province(182102110029)
文摘Impurity formation energy, electronic structure, and photocatalytic properties of C-, N-, or S-doped BiOCl are investigated by density-functional theory plus U calculations(DFT + U). Results show that the doping effect of S is better than that of C or N on the tunable photocatalytic activities of BiOCl. At low concentration, S-doped BiOCl systems are the most stable under Bi-rich growth conditions because of their lower impurity-formation energy. Compared with the electronic structures of S-doped BiOCl, C-or N-doped BiOCl have relatively deeper impurity energy levels appearing in their band gap(except Bi_(36)O_(35)NCl_(36)), which may act as photogenerated carrier-recombination centers and reduce photocatalytic activity. At high concentration, S is substituted on the O lattice site system, whereas some S 3p states mix with the valence band; this mixture leads to an obvious band-gap decrease and continuum-state formation above the valence-band edge of BiOCl. Such activity is advantageous to photochemical catalysis response. Compared with pure Bi OCl and a low-concentration S-doped system, a high-concentration S-doped system shows an obvious redshift on the absorption edge and has better photocatalytic O_2 evolution performance.
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the National Natural Science Foundation of China(No.12375282)the Key Laboratory of Computational Physical Sciences Project(Fudan University),Ministry of Education.
文摘Cs and I can migrate through fuel-cladding interfaces and accelerate the cladding corrosion process induced by the fuel-cladding chemical interaction.Cr coating has emerged as an important candidate for mitigating this chemical interaction.In this study,first-principles calculations were employed to investigate the diffusion behavior of Cs and I in the Cr bulk and grain boundaries to reveal the microscopic interaction mitigation mechanisms at the fuel-cladding interface.The interaction between these two fission products and the Cr coating were studied systematically,and the Cs and I temperature-dependent diffusion coefficients in Cr were obtained using Bocquet’s oversized solute-atom model and Le Claire’s nine-frequency model,respectively.The results showed that the Cs and I migration barriers were significantly lower than that of Cr,and the Cs and I diffusion coefficients were more than three orders of magnitude larger than the Cr self-diffusion coefficient within the temperature range of Generation-IV fast reactors(below 1000 K),demonstrating the strong penetration ability of Cs and I.Furthermore,Cs and I are more likely to diffuse along the grain boundary because of the generally low migration barriers,indicating that the grain boundary serves as a fast diffusion channel for Cs and I.
文摘This study delves into the charge transfer mechanism of boron (B)-doped 3C-SiC through first-principles investigations. We explore the effects of B doping on the electronic properties of 3C-SiC, focusing on a 12.5% impurity concentration. Our comprehensive analysis encompasses structural properties, electronic band structures, and charge density distributions. The optimized lattice constant and band gap energy of 3C-SiC were found to be 4.373 Å and 1.36 eV respectively, which is in agreement with previous research (Bui, 2012;Muchiri et al., 2018). Our results show that B doping narrows the band gap, enhances electrical conductivity, and influences charge transfer interactions. The charge density analysis reveals substantial interactions between B dopants and surrounding carbon atoms. This work not only enhances our understanding of the material’s electronic properties, but also highlights the importance of charge density analysis for characterizing charge transfer mechanisms and their implications in the 3C-SiC semiconductors.
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 Mo2Ga2C are investigated using density func- tional 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 eV. 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 Mo2Ga2C MAX phase are derived from the quasi-harmonic Debye model with phononic effect also for the first time. Analysis of Tc expression using available parameter values (DOS, Debye temperature, atomic mass, etc.) suggests that the compound is less likely to be superconductor.
基金supported by the National Nature Science Foundation of China (No. 50771046)the Foundation from Department of Education of Guangdong Province (No. C10179)
文摘The physical characters and electrochemical properties of various phases in a Sn-Zn electrode, such as formation energy, plateau potential, specific capacity, as well as volume expansion, were calculated by the first-principles plane-wave pseudo-potential method based on the den- sity functional theory. Sn-Zn films were also deposited on copper foils by an electroless plating technique. The actual composition and chemical characters were explored by scanning electron microscopy (SEM), X-ray diffraction (XRD), plasma atomic emission spectrometry (ICP), and constant current charge/discharge measurements (CC). The results show that separation phases with tin and zinc including a small quantity of Cu6Sn5 phase were obtained, the initial lithium insertion capacity of the Sn-Zn film was 661 mAh/g, and obvious potential pla- teaus of about 0.4 V and 0.7 V were displayed, which is in accordance with the results of theoretical calculations. The capacity of the Sn-Zn film decreased seriously with the increase of cycle number.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.90921003,10904004 and 60776063)the Fundamental Research Funds for the Central Universities,China(Grant No.JD1109)
文摘Using first-principles calculations, we systematically study the dissociations of 02 molecules on different ultrathin Pb(lll) films. According to our previous work revealing the molecular adsorption precursor states for O2, we further explore why there are two nearly degenerate adsorption states on Pb(lll) ultrathin films, but no precursor adsorption states existing at all on Mg(0001) and Al(lll) surfaces. The reason is concluded to be the different surface electronic structures. For the O2 dissociation, we consider both the reaction channels from gas-like and molecularly adsorbed O2 molecules. We find that the energy barrier for O2 dissociation from the molecular adsorption precursor states is always smaller than that from O2 gas. The most energetically favorable dissociation process is found to be the same on different Pb(lll) fihns, and the energy barriers are found to be influenced by the quantum size effects of Pb(lll) films.
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financially supported by the National Basic Research Priorities Program of China (No.2007CB936201)the Major Projectof International Cooperation and Exchanges (No.2006DFB51000)the National Natural Science Foundation of China (Nos.50972009 and50972011)
文摘First-principles calculations were performed to investigate the mechanical properties of ZnO nanowires and to study the doping and size effects. A series of strains were applied to ZnO nanowires in the axial direction and the elastic moduli of ZnO nanowires were obtained from the energy versus strain curves. Pure and Mn-doped ZnO nanowires with three different diameters (1.14, 1.43, and 1.74 nm) were studied. It is found that the elastic moduli of the ZnO nanowires are 146.5, 146.6, and 143.9 GPa, respectively, which are slightly larger than that of the bulk (140.1 GPa), and they increase as the diameter decreases. The elastic moduli of the Mn-doped ZnO nanowires are 137.6, 141.8, and 141.0 GPa, which are slightly lower than those of the undoped ones by 6.1%, 3.3%, and 2.0%, respectively. The mechanisms of doping and size effect were discussed in terms of chemical bonding and geometry considerations.
基金supported by the National Natural Science Foundation of China(Grant Nos.11364025 and 11164014)the Gansu Science and Technology PillarProgram,China(Grant No.1204GKCA057)
文摘Using first-principles calculations within density functional theory, we study the atomic structures and electronic properties of the perfect and defective (2VCu+ Incu) CulnGaSe2/CdS interfaces theoretically, especially the interface states. We find that the local lattice structure of (2VCu+ InCu) interface is somewhat disorganized. By analyzing the local density of states projected on several atomic layers of the two interfaces models, we find that for the (2VCu+InCu) interface the interface states near the Fermi level in CulnGaSe2 and CdS band gap regions are mainly composed of interracial Se-4p, Cu-3d and S-3p orbitals, while for the perfect interface there are no clear interface states in the CulnGaSe2 region but only some interface states which are mainly composed of S-3p orbitals in the valance band of CdS region.
基金Project supported by the National Natural Science Foundation of China(Grant No.11864011)the Hubei Provincial Natural Science Foundation of China(Grant No.2018CFB390)the Doctoral Fund Project of Hubei Minzu University,China(Grant No.MY2017B015)
文摘Heterostructures(HSs)have attracted significant attention because of their interlayer van der Waals interactions.The electronic structures and optical properties of stacked GaN-MoS2 HSs under strain have been explored in this work using density functional theory.The results indicate that the direct band gap(1.95 e V)of the Ga N-MoS2 HS is lower than the individual band gaps of both the GaN layer(3.48 e V)and the MoS2 layer(2.03 eV)based on HSE06 hybrid functional calculations.Specifically,the GaN-MoS2 HS is a typical type-II band HS semiconductor that provides an effective approach to enhance the charge separation efficiency for improved photocatalytic degradation activity and water splitting efficiency.Under tensile or compressive strain,the direct band gap of the GaN-MoS2 HS undergoes redshifts.Additionally,the GaN-MoS2 HS maintains its direct band gap semiconductor behavior even when the tensile or compressive strain reaches 5%or-5%.Therefore,the results reported above can be used to expand the application of Ga N-MoS2 HSs to photovoltaic cells and photocatalysts.
基金Project supported by Tianjin Natural Science Fund, China (Grant No. 13JCQNJC00500), the Fundamental Research Funds for the Central Universities, China (Grant No. 65012031), and Tianjin Key Technology R&D Program, China (Grant No. 11ZCKFGX01300).
文摘The geometry, electronic structure and magnetic property of the hexagonal A1N (h-AIN) sheet doped by 5d atoms (Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au and Hg) are investigated by first-principles calculations based on the density functional theory. The influence of symmetry and symmetry-breaking is also studied. There are two types of local symmetries of the doped systems: C3v and D3h. The symmetry will deviate from exact C3,, and D3h for some particular dopants after optimization. The total magnetic moments of the doped systems are 0/-tB for Lu, Ta and It; 1 ~B for Hf, W, Pt and Hg; 2gB for Re and Au; and 3/~B for Os and Al-vacancy. The total densities of state are presented, where impurity energy levels exist. The impurity energy levels and total magnetic moments can be explained by the splitting of 5d orbitals or molecular orbitals under different symmetries.