The phase transition of titanium alloys is sensitive to the heat-treatment procedure,accompanied with the latent heat induced by phase transition.However,the latent heat during phase transition of titanium alloy has n...The phase transition of titanium alloys is sensitive to the heat-treatment procedure,accompanied with the latent heat induced by phase transition.However,the latent heat during phase transition of titanium alloy has not been systematically studied,which may result in the gap between designed and actual temperature of the sample and affect the final mechanical properties.In this work,DSC(differential scanning calorimetry)and first-principles simulate methods were used to study theβ→αphase transition process of TB18(Ti–Al-Mo-V-Cr-Nb-Fe system)metastableβtitanium alloy,especially to reveal the influence of the heating rate on latent heat.The ratio of latent heat to endothermic heat of the sample during temperature rising was introduced to interpret the effect of latent heat to actual temperature.The ratio of latent heat to endothermic heat at 1℃/min is about 15 to 20 times higher than that at 10℃/min.The higher ratio indicates that the latent heat of phase transition has a more significant effect on the temperature,which is related to the temperature range of phase transition and theαvolume fraction.Compared with the heating rate of 1℃/min,theβ→αphase transition takes place at higher temperature and the volume fraction ofαis smaller at 10℃/min.Meanwhile,there is a precipitation free zone between grain boundaryαand intragranularαand the distribution ofαlamellae is heterogeneous when the heating rate is 10℃/min.Both of the experimental and theoretical results suggest that the latent heat of phase transition is the main cause of the temperature fluctuation during heat-treatment process.This work has guiding significance for microstructure optimization affected by temperature,to achieve the desired mechanical properties.展开更多
The ideal tensile strengths of Cr along [001],[110] and [111] directions were calculated based on the first-principles method.The results show that the ideal tensile strengths are 30.83,37.2 and 35.49 GPa for antiferr...The ideal tensile strengths of Cr along [001],[110] and [111] directions were calculated based on the first-principles method.The results show that the ideal tensile strengths are 30.83,37.2 and 35.49 GPa for antiferromagnetic Cr,while they are 33.09,47.15 and38.11 GPa for non-magnetic Cr along [001],[110] and[111] directions,respectively.It is obvious that [001] is the weakest direction.When the loading is applied on the direction [001],the ideal tensile strength is reached before the shear instability for both the anti-ferromagnetic and non-magnetic Cr;thus,Cr fails by cleavage and it is deemed to be intrinsically brittle.Meanwhile,for the antiferromagnetic Cr,the correlation between the magnetic moment and volume was analyzed,and the result shows that the magnetic moment increases with the increase in volume and eventually disappears with the increase in strain.In addition,the density of states in the process of loading was also discussed.展开更多
Earth is a dynamic system. The thermodynamics conditions of Earth vary drastically depending on the depth, ranging from ambient temperature and pressure at the surface to 360 GPa and 6600 K at the core. Consequently, ...Earth is a dynamic system. The thermodynamics conditions of Earth vary drastically depending on the depth, ranging from ambient temperature and pressure at the surface to 360 GPa and 6600 K at the core. Consequently, the physical and chemical properties of Earth’s constituents (e.g., silicate and carbonate minerals) are strongly affected by their immediate environment. In the past 30 years, there has been a tremendous amount of progress in both experimental techniques and theoretical modeling methods for material characterization under extreme conditions. These advancements have elevated our understanding of the properties of minerals, which is essential in order to achieve full comprehension of the formation of this planet and the origin of life on it. This article reviews recent computational techniques for predicting the behavior of materials under extreme conditions. This survey is limited to the application of the first-principles molecular dynamics (FPMD) method to the investigation of chemical and thermodynamic transport processes relevant to Earth Science.展开更多
The development of high-performance solid electrolytes is pivotal for advancing solid-state battery technologies.In this work,we design an oxysulfide-based solid electrolyte Na MgPO_(3)S by combining bond valence theo...The development of high-performance solid electrolytes is pivotal for advancing solid-state battery technologies.In this work,we design an oxysulfide-based solid electrolyte Na MgPO_(3)S by combining bond valence theory and density functional theory calculations.The material features a wide band gap of 4.0 eV and a considerable reduced Na^(+)migration barrier of 0.44 eV,a 1.26-eV decrease compared to pristine Na MgPO_(4)(~1.70 eV).Ab initio molecular dynamics simulations further reveal significantly enhanced ionic conductivity in the oxysulfide-based system compared to the pristine oxide structure.In addition,the calculated decomposition energy indicates that the modified material exhibits good moisture stability.Our findings suggest that sulfur-doping strategy can simultaneously achieve improved ionic conductivity and high moisture stability in oxide solid electrolytes,which could pave the way for designing high-performance solid electrolytes.展开更多
The influence mechanism of trace Nb on the corrosion resistance of surface corrosion products of high-strength anti-seismic rebar in the simulated marine environment was studied by combining first-principles calculati...The influence mechanism of trace Nb on the corrosion resistance of surface corrosion products of high-strength anti-seismic rebar in the simulated marine environment was studied by combining first-principles calculations with corrosion mass loss method,surface analysis,cross-sectional analysis,quantitative analysis,and electrochemical test.The results demonstrated that the addition of trace Nb effectively improved the compactness and stability of surface corrosion layer of rebar,and the corrosion resistance of corrosion layer increased with the increase in Nb content.The beneficial effect of Nb content on the corrosion layer summarized two important key points.Firstly,the addition of Nb was beneficial to promoting the improvement in the structural stability of α-FeOOH,and α-FeOOH structure of solid solution Nb atoms was beneficial to strengthening the fixation of Cl atoms,thus increasing α/(β+γ)ratio,total impedance value,and corrosion potential.Secondly,the formation of Nb oxides can not only repair the corrosion layer,but also play a role in the fixation Cl atoms,resulting in the improvement in corrosion resistance of corrosion layer.展开更多
The mechanical and thermodynamic properties of W-Ti alloys(including W_(15)Ti_(1),W_(14)Ti_(2),W_(12)Ti_(4) and W_(8)Ti_(8) alloys)were investigated by the first-principles approach based on density functional theory....The mechanical and thermodynamic properties of W-Ti alloys(including W_(15)Ti_(1),W_(14)Ti_(2),W_(12)Ti_(4) and W_(8)Ti_(8) alloys)were investigated by the first-principles approach based on density functional theory.The results indicate that W-Ti alloys except W_(8)Ti_(8) are thermodynamically stable.The modulus and hardness of W-Ti alloys are smaller than those of pure tungsten and gradually decrease with increasing Ti concentration.However,their B/G ratios and Poisson's ratios exceed those of pure tungsten,suggesting that the introduction of Ti decreases the mechanical strength while enhancing the ductility of W-Ti alloys.The thermal expansion coefficients for W-Ti alloys all surpass those of pure tungsten,indicating that the introduction of titanium exacerbates the thermal expansion behavior of W-Ti alloys.Nevertheless,elevated pressure has the capacity to suppress the thermal expansion tendencies in titanium-doped tungsten alloys.This study offers theoretical insights for the design of nuclear materials by exploring the mechanical and thermodynamic properties of W-Ti alloys.展开更多
The influence of oxygen defects upon the electronic properties of Nb-doped TiO2 has been studied by using the general gradient approximation （GGA）＋U method. Four independent models （i.e., an undoped anatase cell, ...The influence of oxygen defects upon the electronic properties of Nb-doped TiO2 has been studied by using the general gradient approximation （GGA）＋U method. Four independent models （i.e., an undoped anatase cell, an anatase cell with a Nb dopant at Ti site （NbTi）, an anatase cell with a Nb-dopant and an oxygen vacancy （NbTi＋Vo）, and an anatase cell with a Nb-dopant and an interstitial oxygen （NbTi＋Oi）） were considered. The density of states, effective mass, Bader charge, charge density, and electron localization function were calcul^ited. The results show that in the NbTi＋Vo cell both eg and t2g levels of Ti 3d orbits make contributions to the electronic conductivity, and the oxygen vacancies （Vo） collaborate with Nb-dopants to favor the high electrical conductivity by inducing the Nb-dopants to release more excess charges. In NbTi＋Oi, an unoccupied impurity level appears in the band gap, which served as an acceptor level and suppressed the electronic conductivity. The results qualitatively coincide with experimental results and possibly provide insights into the preparation of TCOs with desirable conductivity.展开更多
Accurately determining the Flade potential(E_(Flade))is of significant importance in the design of novel corrosion-resisting alloys.However,due to the complex nature of the E_(Flade)influenced by several factors inclu...Accurately determining the Flade potential(E_(Flade))is of significant importance in the design of novel corrosion-resisting alloys.However,due to the complex nature of the E_(Flade)influenced by several factors including compositions of the alloys and corrosive solutions,there is currently a lack of truly predictive ab initio model.Here,we established the critical potential condition required for passivation in acidic solutions containing chloride ions(Cl^(-))by developing an ab initio model that incorporates the potential drop from the metal electrode to the solution,considering tunneling of electrons at metal/film interface,breakdown of the film,and electrochemical adsorption reactions at film/solution interface.These parameters were derived from the work function of the alloy substrate and passivation film,the band gap of the passivation film,and the Gibbs free energy of adsorption on the passivation film,all of which can be obtainable from first-principles calculations.This theoretical model has been successfully validated for alloyed stainless steel,exhibiting a remarkable agreement with experimental results.Importantly,enabled by the model,we have identified several alloying elements(i.e.,Ta,W,Os,and Ir)that can effec-tively lower the EFlade of the stainless steel.This work constitutes an important step forward in modeling complex passivation behaviors from first-principles,providing a useful tool for the design of corrosion-resisting alloys.展开更多
Based on first-principles calculation framework,the surface model,anodic dissolution,cathodic oxygen absorption reaction,and other related electrochemical corrosion models of Fe-Ce system were constructed,and the infl...Based on first-principles calculation framework,the surface model,anodic dissolution,cathodic oxygen absorption reaction,and other related electrochemical corrosion models of Fe-Ce system were constructed,and the influencing mechanism Ce doping on the corrosion resistance of Fe-Ce system in the Cl medium environment was analyzed.The results show that Ce doping on the first surface and subsurface inhibits the ionization of Fe atoms and greatly promotes the repassivation process of Fe matrix.Ce doping on the first layer is conducive to preventing the detachment of surface Fe atoms from Fe matrix and delaying the occurrence of corrosion.Ce atoms in the subsurface effectively increase the difficulty of Fe atoms detaching from the matrix at high Cl concentrations.When O diffusion is the controlling link of oxygen absorption reaction,Ce doping has no effects on the reaction rate of cathodic oxygen absorption.Ce doping enhances the electrochemical stability of Fe(100)1and reduces the anodic dissolution rate of Fe matrix,thereby improving its corrosion resistance.展开更多
The vacuum reactive wetting and brazing of Er_(2)Si_(2)O_(7)/MoSi_(2) coatings were investigated using a (CoFeNiCrMn)_(88)Nb_(12) high-entropy alloy (HEA) brazing filler. The microstructural evolution and wettability ...The vacuum reactive wetting and brazing of Er_(2)Si_(2)O_(7)/MoSi_(2) coatings were investigated using a (CoFeNiCrMn)_(88)Nb_(12) high-entropy alloy (HEA) brazing filler. The microstructural evolution and wettability of the HEA filler were analyzed, with particular attention to the surface energy, interfacial stability, and electronic properties of the HEA filler/rare earth silicate coating system, as determined by density functional theory (DFT). As Nb diffused into the interface and the ErNbO_(4) phase formed, the wetting angle gradually decreased to 23.12° The effective wetting and spreading of the HEA brazing filler on the rare earth silicate coating surface are strongly correlated with the formation of the ErNbO_(4) phase at the interface. Furthermore, DFT calculations reveal that the interfacial bonding energy between the BCC' and FCC' phases and the ErNbO_(4) phase, after the wetting reaction, is significantly higher than the bonding energy between the initial filler and Er_(2)Si_(2)O_(7). This finding suggests that the formation of the ErNbO_(4) phase improves the wetting and spreading behavior of the filler.展开更多
Control of hyperfine interaction strength of shallow donors in Si is one of the central issues in realizing Kane quantum computers.First-principles calculations on the hyperfine Stark shift of shallow donors are chall...Control of hyperfine interaction strength of shallow donors in Si is one of the central issues in realizing Kane quantum computers.First-principles calculations on the hyperfine Stark shift of shallow donors are challenging since large supercells are needed to accommodate the delocalized donor wave functions.In this work,we investigated the hyperfine Stark shift and its strain tunability for shallow donors P and As in Si using the potential patching method based on first-principles density functional theory calculations.The good agreement between our calculations and experimental results confirms that the potential patching method is a feasible and accurate first-principles approach for studying wave-function-related properties of shallow impurities,such as the Stark shift parameter.It is further shown that the application of strain expands the range of hyperfine Stark shift and helps improve the response of shallow donor based qubit gates.The results could be useful for developing quantum computing architectures based on shallow donors in Si.展开更多
The adsorption properties of a magnesium porphyrin(MgP)molecule on Au(111)surface covered with up to three lay-ers of sodium chloride(NaCl)were investigated by means of first-principles calculations.The most stable ad...The adsorption properties of a magnesium porphyrin(MgP)molecule on Au(111)surface covered with up to three lay-ers of sodium chloride(NaCl)were investigated by means of first-principles calculations.The most stable adsorption configuration of MgP on the NaCl/Au(111)heterosurfaces was found to be at the Cl-top site with a 20°angle between the[110]lattice direction of NaCl and the Mg–N bond of the molecule.Compared with MgP molecule adsorbed on bare Au(111),the inclusion of NaCl lay-ers can lead to a significant decrease in the adsorption energy of the MgP molecule.The exis-tence of NaCl layers also reduced the charge transfer between the molecule and the surface.For heterosurfaces with two or three monolayers of NaCl,the charge transfer was almost com-pletely suppressed.The obtained partial density of states(PDOS)showed that hybridization between the electronic structures of the adsorbed MgP molecule and the metal surface can be significantly suppressed when NaCl layers were added.For the heterosurface with three lay-ers of NaCl,the PDOS around the Fermi level was almost identical with that of the free molecule,suggesting the electronic structure of the MgP molecule was nicely preserved.Influ-ence of the NaCl layers on the electronic structure of the MgP molecule was mainly found for molecular orbitals(MOs)away from the Fermi level as a result of the large band gap of the NaCl layers.展开更多
Solute segregation at grain boundaries(GBs)can significantly influence GB cohesion.In this work,the segregation energies of solutes(Zn,Al,Ag,Ca,and Gd)were first investigated at six symmetrical tilt GBs rotating aroun...Solute segregation at grain boundaries(GBs)can significantly influence GB cohesion.In this work,the segregation energies of solutes(Zn,Al,Ag,Ca,and Gd)were first investigated at six symmetrical tilt GBs rotating around[0001]axis of Mg,to uncover the impact of GB characteristics on solute segregation behavior.The results reveal that solute segregation propensity is closely related to the local geometric environment of GB sites,but has little correlation with intrinsic GB properties(such as GB misorientation and GB energy).Furthermore,relationships between GB site characteristics and solute segregation tendencies were established.Ca-like solutes tend to occupy GB sites with larger Voronoi volumes(V),while Zn-like solutes prefer GB sites with smaller V as well as smaller shortest bond lengths(SBL).Based on this finding,we further evaluated the segregation capacities of 26 solutes at their most energetically stable segregation sites and their impact on GB cohesion.A descriptor that can effectively capture the strengthening/embrittling potency of segregated solutes on GBs was proposed by performing the crystal orbital Hamilton population(COHP)analyses.It was found that the discrepancies in bond strength between GBs and free surface dominate the solute-strengthening behavior.Finally,a first-principles“design map”regarding the segregation energies and strengthening energies was provided,which offers a database for designing Mg alloys with high fracture toughness.展开更多
Ni-Mn-Ti Heusler alloys have great potential for elastocaloric refrigeration due to the colossal caloric effect and good mechanical properties. However, theoretical calculations on the characterization of the elastoca...Ni-Mn-Ti Heusler alloys have great potential for elastocaloric refrigeration due to the colossal caloric effect and good mechanical properties. However, theoretical calculations on the characterization of the elastocaloric effect are rare. An important parameter to evaluate the elastocaloric effect is the transformation entropy change, whose main source is the vibrational entropy change (ΔS_(vib)). Unfortunately, the widely used quasiharmonic approximation method fails in the prediction of the vibrational entropy for high-temperature austenite due to its dynamical instability at 0 K. To solve this problem, the temperature dependent effective potential method was used considering the temperature and anharmonic effect. Sc, V, and Zr doping at the Ti sites in B2 disordered Ni_(8)Mn_(5)Ti_(3) were studied about phase stability, martensitic transformation, and elastocaloric properties. The results revealed the austenitic structures of all the doping systems exhibit antiferromagnetic coupling characteristics at 300 K due to the temperature effect. Sc and Zr doping at the Ti sites decreased the ΔS_(vib) value, whereas V doping at the Ti site increased the ΔS_(vib) value. Further analysis proved the important evaluation criterion that the ΔS_(vib) value increases with the tetragonal distortion ratio and volume change, which has important guiding significance for improving the elastocaloric effect. Besides, the calculations of elastic constants presented all the doping systems maintain outstanding ductility evaluated from the B/G ratio. This work provides an effective strategy for designing excellent elastocaloric material with large vibrational entropy change and good mechanical properties.展开更多
Thermal expansion is crucial for various industrial processes and is increasingly the focus of research endeavors aimed at improving material performance.However,it is the continuous advancements in first-principles c...Thermal expansion is crucial for various industrial processes and is increasingly the focus of research endeavors aimed at improving material performance.However,it is the continuous advancements in first-principles calculations that have enabled researchers to understand the microscopic origins of thermal expansion.In this study,we propose a coefficient of thermal expansion(CTE)calculation scheme based on self-consistent phonon theory,incorporating the fourth-order anharmonicity.We selected four structures(Si,CaZrF_(6),SrTiO_(3),NaBr)to investigate high-order anharmonicity’s impact on their CTEs,based on bonding types.The results indicate that our method goes beyond the second-order quasi-harmonic approximation and the third-order perturbation theory,aligning closely with experimental data.Furthermore,we observed that an increase in the ionicity of the structures leads to a more pronounced influence of high-order anharmonicity on CTE,with this effect primarily manifesting in variations of the Grüneisen parameter.Our research provides a theoretical foundation for accurately predicting and regulating the thermal expansion behavior of materials.展开更多
In this study,6061 aluminum alloy and galvanized steel fusion-brazed lap joints were obtained using a laser-arc hybrid heat source,and the effects of laser power variation on the microstructure,mechanical properties,a...In this study,6061 aluminum alloy and galvanized steel fusion-brazed lap joints were obtained using a laser-arc hybrid heat source,and the effects of laser power variation on the microstructure,mechanical properties,and fracture mechanism of the joints were ana-lyzed.The results showed that the tensile shear load initially increased with rising laser power,followed by a decrease.At a laser power of 240 W,the maximum tensile shear load was 2479.8 N/cm and the weak section of joint was in the Al-Fe reaction layer con-sisting of Fe(Al,Si)_(3),Fe_(2)(Al,Si)_(5),and Fe(Al,Si)intermetallic compounds(IMCs).Computational results showed that the inherently high brittleness and hardness of Fe(Al,Si)_(3) and the high mismatch rates of Fe(Al,Si)_(3)/Al interfaces were the key factor leading to the failure of the joints at lower heat input.展开更多
Second period elements(B,C,N,and O)usually appear at the grain boundary(GB)and strongly affect the mechanical performance in austenitic stainless steels.Therefore,it is significant to investigate the effect of solute ...Second period elements(B,C,N,and O)usually appear at the grain boundary(GB)and strongly affect the mechanical performance in austenitic stainless steels.Therefore,it is significant to investigate the effect of solute elements(B,C,N,and O)on the GB.The first-principles calculation based on the density function theory was applied to explore the effect of B,C,N,and O onγ-FeΣ5(210)[001]GB.The GB energy,the segregation energy,the Voronoi volume,and the theoretical tensile test were calculated to investigate the segregation behavior and the strengthening effect.The structural change and electronic evolution were also investigated by bond change,charge density distribution,and density of states.The results show that B is favored to segregate at the capped trigonal prism(CTP)position with a large void and has a strengthening effect on the GB strength,while O and N are preferred to locate at the octahedral(OCT)site and have an embrittling effect on GB cohesion.C can segregate at both the CTP site and the OCT location with little energy difference.As C segregates at the OCT site,it is beneficial for GB strength.However,it is detrimental at the CTP position.It can be seen that the influence of solutes is closely related to the element type and segregated position.展开更多
MgO is one of the most abundant minerals in the Earth’s interior,and its structure and properties at high temperature and pressure are important for us to understand the composition and behavior in the deep Earth.In ...MgO is one of the most abundant minerals in the Earth’s interior,and its structure and properties at high temperature and pressure are important for us to understand the composition and behavior in the deep Earth.In the present work,firstprinciples molecular dynamics calculations were performed to investigate the pressure-induced structural evolution of the MgO melts at 4000 K and 5000 K.The results predicted the liquid-solid phase boundaries,and the calculated viscosities of the melts may help us to understand the transport behavior under the corresponding Earth conditions.展开更多
Herein,a first-principles investigation was innovatively conducted to research the surface oxidation of ZnS-like sphalerite in the absence and presence of H_(2)O .The findings showed that single O_(2) was preferred to...Herein,a first-principles investigation was innovatively conducted to research the surface oxidation of ZnS-like sphalerite in the absence and presence of H_(2)O .The findings showed that single O_(2) was preferred to be dissociated adsorption on sphalerite surface by generating SAO and Zn AO bonds,and the S atom on the surface was the most energy-supported site for O_(2) adsorption,on which a≡Zn-O-S-O-Zn≡structure will be formed.However,dissociated adsorption of single H_(2)O will not happen.It was preferred to be adsorbed on the top Zn atom on sphalerite surface in molecular form through Zn-O bond.Besides,sphalerite oxidation can occur as if O_(2) was present regardless of the presence of H_(2)O ,and when H_(2)O and O_(2) coexisted,the formation of sulfur oxide(SO_(2) )needed a lower energy barrier and it was easier to form on sphalerite surface than that only O_(2) existed.In the absence of H_(2)O ,when SO_(2) was generated,further oxidation of which would form neutral zinc sulfate.In the presence of H_(2)O ,the formation of SO_(2) on sphalerite surface was easier and the rate of further oxidation to form sulfate was also greater.Consequently,the occurrence of sphalerite oxidation was accelerated.展开更多
基金the Strategic Priority Research Program of the Chinese Academy of Sciences(XDA22010101)the National Key Research and Development Program of China(2021YFC2801801)+1 种基金the CAS Project for Young Scientists in Basic Research(YSBR-025),the Natural Science Foundation of China(51871225)the Youth Innovation Promotion Association CAS and Liaoning Revitalization Talents Program(XLYC1907005).
文摘The phase transition of titanium alloys is sensitive to the heat-treatment procedure,accompanied with the latent heat induced by phase transition.However,the latent heat during phase transition of titanium alloy has not been systematically studied,which may result in the gap between designed and actual temperature of the sample and affect the final mechanical properties.In this work,DSC(differential scanning calorimetry)and first-principles simulate methods were used to study theβ→αphase transition process of TB18(Ti–Al-Mo-V-Cr-Nb-Fe system)metastableβtitanium alloy,especially to reveal the influence of the heating rate on latent heat.The ratio of latent heat to endothermic heat of the sample during temperature rising was introduced to interpret the effect of latent heat to actual temperature.The ratio of latent heat to endothermic heat at 1℃/min is about 15 to 20 times higher than that at 10℃/min.The higher ratio indicates that the latent heat of phase transition has a more significant effect on the temperature,which is related to the temperature range of phase transition and theαvolume fraction.Compared with the heating rate of 1℃/min,theβ→αphase transition takes place at higher temperature and the volume fraction ofαis smaller at 10℃/min.Meanwhile,there is a precipitation free zone between grain boundaryαand intragranularαand the distribution ofαlamellae is heterogeneous when the heating rate is 10℃/min.Both of the experimental and theoretical results suggest that the latent heat of phase transition is the main cause of the temperature fluctuation during heat-treatment process.This work has guiding significance for microstructure optimization affected by temperature,to achieve the desired mechanical properties.
基金financially supported by the National Natural Science Foundation of China (No.51371017)。
文摘The ideal tensile strengths of Cr along [001],[110] and [111] directions were calculated based on the first-principles method.The results show that the ideal tensile strengths are 30.83,37.2 and 35.49 GPa for antiferromagnetic Cr,while they are 33.09,47.15 and38.11 GPa for non-magnetic Cr along [001],[110] and[111] directions,respectively.It is obvious that [001] is the weakest direction.When the loading is applied on the direction [001],the ideal tensile strength is reached before the shear instability for both the anti-ferromagnetic and non-magnetic Cr;thus,Cr fails by cleavage and it is deemed to be intrinsically brittle.Meanwhile,for the antiferromagnetic Cr,the correlation between the magnetic moment and volume was analyzed,and the result shows that the magnetic moment increases with the increase in volume and eventually disappears with the increase in strain.In addition,the density of states in the process of loading was also discussed.
文摘Earth is a dynamic system. The thermodynamics conditions of Earth vary drastically depending on the depth, ranging from ambient temperature and pressure at the surface to 360 GPa and 6600 K at the core. Consequently, the physical and chemical properties of Earth’s constituents (e.g., silicate and carbonate minerals) are strongly affected by their immediate environment. In the past 30 years, there has been a tremendous amount of progress in both experimental techniques and theoretical modeling methods for material characterization under extreme conditions. These advancements have elevated our understanding of the properties of minerals, which is essential in order to achieve full comprehension of the formation of this planet and the origin of life on it. This article reviews recent computational techniques for predicting the behavior of materials under extreme conditions. This survey is limited to the application of the first-principles molecular dynamics (FPMD) method to the investigation of chemical and thermodynamic transport processes relevant to Earth Science.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.22473010,22303114,and 12474372)the Fundamental Research Funds for the Central Universities,Jilin University,the National Key Research and Development Program of China(Grant No.SQ2023YFB2805600)+4 种基金the Natural Science Foundation of Beijing Municipality(Grant No.Z210004)the Fund from the State Key Laboratory of Information Photonics and Optical Communications(Grant No.IPOC2021ZT01)Beijing Nova Program from Beijing Municipal Science and Technology Commission(Grant No.20230484433)Beijing University of Posts and Telecommunications Excellent Ph.D.Students Foundation(Grant No.CX20241078)Beijing Natural Science Foundation(Undergraduate Program)(Grant No.QY24218)。
文摘The development of high-performance solid electrolytes is pivotal for advancing solid-state battery technologies.In this work,we design an oxysulfide-based solid electrolyte Na MgPO_(3)S by combining bond valence theory and density functional theory calculations.The material features a wide band gap of 4.0 eV and a considerable reduced Na^(+)migration barrier of 0.44 eV,a 1.26-eV decrease compared to pristine Na MgPO_(4)(~1.70 eV).Ab initio molecular dynamics simulations further reveal significantly enhanced ionic conductivity in the oxysulfide-based system compared to the pristine oxide structure.In addition,the calculated decomposition energy indicates that the modified material exhibits good moisture stability.Our findings suggest that sulfur-doping strategy can simultaneously achieve improved ionic conductivity and high moisture stability in oxide solid electrolytes,which could pave the way for designing high-performance solid electrolytes.
基金supported by National Natural Science Foundation of China(Grant No.52074095)Guizhou Provincial Basic Research Program(Natural Science)(Grant No.QKHJC-ZK[2023]YB072)+2 种基金Guizhou Provincial Key Technology R&D Program(Grant No.QKHZC[2023]YB404)Guizhou Provincial Key Technology R&D Program(Grant No.QKHZC[2022]YB053)The numerical calculation of the first-principles was supported and assisted by the High-Performance Computing Center of Guizhou University.
文摘The influence mechanism of trace Nb on the corrosion resistance of surface corrosion products of high-strength anti-seismic rebar in the simulated marine environment was studied by combining first-principles calculations with corrosion mass loss method,surface analysis,cross-sectional analysis,quantitative analysis,and electrochemical test.The results demonstrated that the addition of trace Nb effectively improved the compactness and stability of surface corrosion layer of rebar,and the corrosion resistance of corrosion layer increased with the increase in Nb content.The beneficial effect of Nb content on the corrosion layer summarized two important key points.Firstly,the addition of Nb was beneficial to promoting the improvement in the structural stability of α-FeOOH,and α-FeOOH structure of solid solution Nb atoms was beneficial to strengthening the fixation of Cl atoms,thus increasing α/(β+γ)ratio,total impedance value,and corrosion potential.Secondly,the formation of Nb oxides can not only repair the corrosion layer,but also play a role in the fixation Cl atoms,resulting in the improvement in corrosion resistance of corrosion layer.
基金Funded by National Key R&D Program of China(No.2021YFB3802300)the National Natural Science Foundation of China(No.52171045)the Joint Fund(No.8091B022108)。
文摘The mechanical and thermodynamic properties of W-Ti alloys(including W_(15)Ti_(1),W_(14)Ti_(2),W_(12)Ti_(4) and W_(8)Ti_(8) alloys)were investigated by the first-principles approach based on density functional theory.The results indicate that W-Ti alloys except W_(8)Ti_(8) are thermodynamically stable.The modulus and hardness of W-Ti alloys are smaller than those of pure tungsten and gradually decrease with increasing Ti concentration.However,their B/G ratios and Poisson's ratios exceed those of pure tungsten,suggesting that the introduction of Ti decreases the mechanical strength while enhancing the ductility of W-Ti alloys.The thermal expansion coefficients for W-Ti alloys all surpass those of pure tungsten,indicating that the introduction of titanium exacerbates the thermal expansion behavior of W-Ti alloys.Nevertheless,elevated pressure has the capacity to suppress the thermal expansion tendencies in titanium-doped tungsten alloys.This study offers theoretical insights for the design of nuclear materials by exploring the mechanical and thermodynamic properties of W-Ti alloys.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51002135 and 51172200)the Fundamental Research Funds for the Central Universities of Ministry of Education of China(Grant No.2013QNA4011)
文摘The influence of oxygen defects upon the electronic properties of Nb-doped TiO2 has been studied by using the general gradient approximation （GGA）＋U method. Four independent models （i.e., an undoped anatase cell, an anatase cell with a Nb dopant at Ti site （NbTi）, an anatase cell with a Nb-dopant and an oxygen vacancy （NbTi＋Vo）, and an anatase cell with a Nb-dopant and an interstitial oxygen （NbTi＋Oi）） were considered. The density of states, effective mass, Bader charge, charge density, and electron localization function were calcul^ited. The results show that in the NbTi＋Vo cell both eg and t2g levels of Ti 3d orbits make contributions to the electronic conductivity, and the oxygen vacancies （Vo） collaborate with Nb-dopants to favor the high electrical conductivity by inducing the Nb-dopants to release more excess charges. In NbTi＋Oi, an unoccupied impurity level appears in the band gap, which served as an acceptor level and suppressed the electronic conductivity. The results qualitatively coincide with experimental results and possibly provide insights into the preparation of TCOs with desirable conductivity.
基金supported by the Natural Science Foundation Project of Liaoning province(Nos.2023-MS-017 and 2022-MS-005)the National Science and Technology Major Project(No.J2019-VI-0019-0134)+2 种基金the National Natural Science Foundation of China(Nos.52201028 and 52188101)the Project funded by China Postdoctoral Science Foundation(No.2021M700153)the Special Projects of the Central Government in Guidance of Local Science and Technology Development(No.2024010859-JH6/1006).
文摘Accurately determining the Flade potential(E_(Flade))is of significant importance in the design of novel corrosion-resisting alloys.However,due to the complex nature of the E_(Flade)influenced by several factors including compositions of the alloys and corrosive solutions,there is currently a lack of truly predictive ab initio model.Here,we established the critical potential condition required for passivation in acidic solutions containing chloride ions(Cl^(-))by developing an ab initio model that incorporates the potential drop from the metal electrode to the solution,considering tunneling of electrons at metal/film interface,breakdown of the film,and electrochemical adsorption reactions at film/solution interface.These parameters were derived from the work function of the alloy substrate and passivation film,the band gap of the passivation film,and the Gibbs free energy of adsorption on the passivation film,all of which can be obtainable from first-principles calculations.This theoretical model has been successfully validated for alloyed stainless steel,exhibiting a remarkable agreement with experimental results.Importantly,enabled by the model,we have identified several alloying elements(i.e.,Ta,W,Os,and Ir)that can effec-tively lower the EFlade of the stainless steel.This work constitutes an important step forward in modeling complex passivation behaviors from first-principles,providing a useful tool for the design of corrosion-resisting alloys.
基金Project supported by the National Natural Science Foundation of China(52364044,52204364)Scientific Research Special Project for First-Class Disciplines of Education Department of Inner Mongolia Autonomous Region(YLXKZX-NKD-001,YLXKZX-NKD-011)Basic Scientific Research Business Expenses of Colleges and Universities of Inner Mongolia Autonomous Region(2023QNJS011)。
文摘Based on first-principles calculation framework,the surface model,anodic dissolution,cathodic oxygen absorption reaction,and other related electrochemical corrosion models of Fe-Ce system were constructed,and the influencing mechanism Ce doping on the corrosion resistance of Fe-Ce system in the Cl medium environment was analyzed.The results show that Ce doping on the first surface and subsurface inhibits the ionization of Fe atoms and greatly promotes the repassivation process of Fe matrix.Ce doping on the first layer is conducive to preventing the detachment of surface Fe atoms from Fe matrix and delaying the occurrence of corrosion.Ce atoms in the subsurface effectively increase the difficulty of Fe atoms detaching from the matrix at high Cl concentrations.When O diffusion is the controlling link of oxygen absorption reaction,Ce doping has no effects on the reaction rate of cathodic oxygen absorption.Ce doping enhances the electrochemical stability of Fe(100)1and reduces the anodic dissolution rate of Fe matrix,thereby improving its corrosion resistance.
基金support from the National Natural Science Foundation of China(No.52374402)the National Key Research and Development Program(No.2022YFB3402200)+2 种基金the National Science and Technology Major Project(No.J2022-VII-0003-0045)the Project of Key areas of innovation team in Shaanxi Province(No.2024RS-CXTD-20)the Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University(No.CX2024055).
文摘The vacuum reactive wetting and brazing of Er_(2)Si_(2)O_(7)/MoSi_(2) coatings were investigated using a (CoFeNiCrMn)_(88)Nb_(12) high-entropy alloy (HEA) brazing filler. The microstructural evolution and wettability of the HEA filler were analyzed, with particular attention to the surface energy, interfacial stability, and electronic properties of the HEA filler/rare earth silicate coating system, as determined by density functional theory (DFT). As Nb diffused into the interface and the ErNbO_(4) phase formed, the wetting angle gradually decreased to 23.12° The effective wetting and spreading of the HEA brazing filler on the rare earth silicate coating surface are strongly correlated with the formation of the ErNbO_(4) phase at the interface. Furthermore, DFT calculations reveal that the interfacial bonding energy between the BCC' and FCC' phases and the ErNbO_(4) phase, after the wetting reaction, is significantly higher than the bonding energy between the initial filler and Er_(2)Si_(2)O_(7). This finding suggests that the formation of the ErNbO_(4) phase improves the wetting and spreading behavior of the filler.
基金supported by the National Natural Science Foun-dation of China(Grant Nos.12393831 and 12088101).
文摘Control of hyperfine interaction strength of shallow donors in Si is one of the central issues in realizing Kane quantum computers.First-principles calculations on the hyperfine Stark shift of shallow donors are challenging since large supercells are needed to accommodate the delocalized donor wave functions.In this work,we investigated the hyperfine Stark shift and its strain tunability for shallow donors P and As in Si using the potential patching method based on first-principles density functional theory calculations.The good agreement between our calculations and experimental results confirms that the potential patching method is a feasible and accurate first-principles approach for studying wave-function-related properties of shallow impurities,such as the Stark shift parameter.It is further shown that the application of strain expands the range of hyperfine Stark shift and helps improve the response of shallow donor based qubit gates.The results could be useful for developing quantum computing architectures based on shallow donors in Si.
基金supported by the National Natural Science Foundation of China(No.22373084,No.62201494)Hebei Natural Science Foundation(B2022203007)the Cultivation Project for Basic Research and Innovation of Yanshan University(2024LGZD002).
文摘The adsorption properties of a magnesium porphyrin(MgP)molecule on Au(111)surface covered with up to three lay-ers of sodium chloride(NaCl)were investigated by means of first-principles calculations.The most stable adsorption configuration of MgP on the NaCl/Au(111)heterosurfaces was found to be at the Cl-top site with a 20°angle between the[110]lattice direction of NaCl and the Mg–N bond of the molecule.Compared with MgP molecule adsorbed on bare Au(111),the inclusion of NaCl lay-ers can lead to a significant decrease in the adsorption energy of the MgP molecule.The exis-tence of NaCl layers also reduced the charge transfer between the molecule and the surface.For heterosurfaces with two or three monolayers of NaCl,the charge transfer was almost com-pletely suppressed.The obtained partial density of states(PDOS)showed that hybridization between the electronic structures of the adsorbed MgP molecule and the metal surface can be significantly suppressed when NaCl layers were added.For the heterosurface with three lay-ers of NaCl,the PDOS around the Fermi level was almost identical with that of the free molecule,suggesting the electronic structure of the MgP molecule was nicely preserved.Influ-ence of the NaCl layers on the electronic structure of the MgP molecule was mainly found for molecular orbitals(MOs)away from the Fermi level as a result of the large band gap of the NaCl layers.
基金supported by the National Natural Science Foundation of China(Nos.52222409 and U24A20104)the National Key Research and Development Program(No.2024YFB3408900)+1 种基金Partial financial support came from the Fundamental Research Funds for the Central Universities,JLUsupported by the High Performance Computing Center of Jilin University,China.
文摘Solute segregation at grain boundaries(GBs)can significantly influence GB cohesion.In this work,the segregation energies of solutes(Zn,Al,Ag,Ca,and Gd)were first investigated at six symmetrical tilt GBs rotating around[0001]axis of Mg,to uncover the impact of GB characteristics on solute segregation behavior.The results reveal that solute segregation propensity is closely related to the local geometric environment of GB sites,but has little correlation with intrinsic GB properties(such as GB misorientation and GB energy).Furthermore,relationships between GB site characteristics and solute segregation tendencies were established.Ca-like solutes tend to occupy GB sites with larger Voronoi volumes(V),while Zn-like solutes prefer GB sites with smaller V as well as smaller shortest bond lengths(SBL).Based on this finding,we further evaluated the segregation capacities of 26 solutes at their most energetically stable segregation sites and their impact on GB cohesion.A descriptor that can effectively capture the strengthening/embrittling potency of segregated solutes on GBs was proposed by performing the crystal orbital Hamilton population(COHP)analyses.It was found that the discrepancies in bond strength between GBs and free surface dominate the solute-strengthening behavior.Finally,a first-principles“design map”regarding the segregation energies and strengthening energies was provided,which offers a database for designing Mg alloys with high fracture toughness.
基金supported by the National Natural Science Foundation of China(Nos.52271172,and 51971085).
文摘Ni-Mn-Ti Heusler alloys have great potential for elastocaloric refrigeration due to the colossal caloric effect and good mechanical properties. However, theoretical calculations on the characterization of the elastocaloric effect are rare. An important parameter to evaluate the elastocaloric effect is the transformation entropy change, whose main source is the vibrational entropy change (ΔS_(vib)). Unfortunately, the widely used quasiharmonic approximation method fails in the prediction of the vibrational entropy for high-temperature austenite due to its dynamical instability at 0 K. To solve this problem, the temperature dependent effective potential method was used considering the temperature and anharmonic effect. Sc, V, and Zr doping at the Ti sites in B2 disordered Ni_(8)Mn_(5)Ti_(3) were studied about phase stability, martensitic transformation, and elastocaloric properties. The results revealed the austenitic structures of all the doping systems exhibit antiferromagnetic coupling characteristics at 300 K due to the temperature effect. Sc and Zr doping at the Ti sites decreased the ΔS_(vib) value, whereas V doping at the Ti site increased the ΔS_(vib) value. Further analysis proved the important evaluation criterion that the ΔS_(vib) value increases with the tetragonal distortion ratio and volume change, which has important guiding significance for improving the elastocaloric effect. Besides, the calculations of elastic constants presented all the doping systems maintain outstanding ductility evaluated from the B/G ratio. This work provides an effective strategy for designing excellent elastocaloric material with large vibrational entropy change and good mechanical properties.
基金Project supported by the National Natural Science Foundation of China(Grant No.62125402).
文摘Thermal expansion is crucial for various industrial processes and is increasingly the focus of research endeavors aimed at improving material performance.However,it is the continuous advancements in first-principles calculations that have enabled researchers to understand the microscopic origins of thermal expansion.In this study,we propose a coefficient of thermal expansion(CTE)calculation scheme based on self-consistent phonon theory,incorporating the fourth-order anharmonicity.We selected four structures(Si,CaZrF_(6),SrTiO_(3),NaBr)to investigate high-order anharmonicity’s impact on their CTEs,based on bonding types.The results indicate that our method goes beyond the second-order quasi-harmonic approximation and the third-order perturbation theory,aligning closely with experimental data.Furthermore,we observed that an increase in the ionicity of the structures leads to a more pronounced influence of high-order anharmonicity on CTE,with this effect primarily manifesting in variations of the Grüneisen parameter.Our research provides a theoretical foundation for accurately predicting and regulating the thermal expansion behavior of materials.
基金supported by the National Key Research and Development Program of China(No.2022YFB4600900).
文摘In this study,6061 aluminum alloy and galvanized steel fusion-brazed lap joints were obtained using a laser-arc hybrid heat source,and the effects of laser power variation on the microstructure,mechanical properties,and fracture mechanism of the joints were ana-lyzed.The results showed that the tensile shear load initially increased with rising laser power,followed by a decrease.At a laser power of 240 W,the maximum tensile shear load was 2479.8 N/cm and the weak section of joint was in the Al-Fe reaction layer con-sisting of Fe(Al,Si)_(3),Fe_(2)(Al,Si)_(5),and Fe(Al,Si)intermetallic compounds(IMCs).Computational results showed that the inherently high brittleness and hardness of Fe(Al,Si)_(3) and the high mismatch rates of Fe(Al,Si)_(3)/Al interfaces were the key factor leading to the failure of the joints at lower heat input.
基金supported by National Key R&D Program of China(No.2022YFB3705202)National Natural Science Foundation of China(Nos.51831008,52171049 and 52104330).
文摘Second period elements(B,C,N,and O)usually appear at the grain boundary(GB)and strongly affect the mechanical performance in austenitic stainless steels.Therefore,it is significant to investigate the effect of solute elements(B,C,N,and O)on the GB.The first-principles calculation based on the density function theory was applied to explore the effect of B,C,N,and O onγ-FeΣ5(210)[001]GB.The GB energy,the segregation energy,the Voronoi volume,and the theoretical tensile test were calculated to investigate the segregation behavior and the strengthening effect.The structural change and electronic evolution were also investigated by bond change,charge density distribution,and density of states.The results show that B is favored to segregate at the capped trigonal prism(CTP)position with a large void and has a strengthening effect on the GB strength,while O and N are preferred to locate at the octahedral(OCT)site and have an embrittling effect on GB cohesion.C can segregate at both the CTP site and the OCT location with little energy difference.As C segregates at the OCT site,it is beneficial for GB strength.However,it is detrimental at the CTP position.It can be seen that the influence of solutes is closely related to the element type and segregated position.
基金supported by the National Natural Science Foundation of China(Grant No.51701180)the Foundation of the State Key Laboratory of Coal Conversion(Grant No.J22-23-103).
文摘MgO is one of the most abundant minerals in the Earth’s interior,and its structure and properties at high temperature and pressure are important for us to understand the composition and behavior in the deep Earth.In the present work,firstprinciples molecular dynamics calculations were performed to investigate the pressure-induced structural evolution of the MgO melts at 4000 K and 5000 K.The results predicted the liquid-solid phase boundaries,and the calculated viscosities of the melts may help us to understand the transport behavior under the corresponding Earth conditions.
基金supported by the Postdoctoral Fellowship Program(Grade A)of China Postdoctoral Science Foundation(No.BX20240429)the National Science and Technology Major Project of the Ministry of Science and Technology of China(No.2024ZD1004007)+3 种基金the National Key R&D Program of China(Nos.2022YFC2904502 and 2022YFC2904501)the National Natural Science Foundation of China(No.52204298)the Major Science and Technology Projects in Yunnan Province(No.202202AB080012)the High Performance Computing Center of Central South University。
文摘Herein,a first-principles investigation was innovatively conducted to research the surface oxidation of ZnS-like sphalerite in the absence and presence of H_(2)O .The findings showed that single O_(2) was preferred to be dissociated adsorption on sphalerite surface by generating SAO and Zn AO bonds,and the S atom on the surface was the most energy-supported site for O_(2) adsorption,on which a≡Zn-O-S-O-Zn≡structure will be formed.However,dissociated adsorption of single H_(2)O will not happen.It was preferred to be adsorbed on the top Zn atom on sphalerite surface in molecular form through Zn-O bond.Besides,sphalerite oxidation can occur as if O_(2) was present regardless of the presence of H_(2)O ,and when H_(2)O and O_(2) coexisted,the formation of sulfur oxide(SO_(2) )needed a lower energy barrier and it was easier to form on sphalerite surface than that only O_(2) existed.In the absence of H_(2)O ,when SO_(2) was generated,further oxidation of which would form neutral zinc sulfate.In the presence of H_(2)O ,the formation of SO_(2) on sphalerite surface was easier and the rate of further oxidation to form sulfate was also greater.Consequently,the occurrence of sphalerite oxidation was accelerated.
