Lattice constants, total energies, and densities of state of transition metals Co, Rh, and Ir in the VⅢB group with different crystalline structures were calculated via generalized gradient approximation (GGA) of t...Lattice constants, total energies, and densities of state of transition metals Co, Rh, and Ir in the VⅢB group with different crystalline structures were calculated via generalized gradient approximation (GGA) of the total energy plane wave pseudopotential method in first-principles. The lattice stabilities of Rh and Ir are ΔG^ bcc-hcp 〉 Δ G^fcc-hcp 〉 0, agreeing well with those of the projector augmented wave method in first-principles and the CALPHAD method in spite of elemental Co. Analyses of the electronic structures to lattice stability show that crystalline Rh and Ir with fcc structures have the obvious characteristic of a stable phase, agreeing with the results of total energy calculations. Analyses of atomic populations show that the transition rate of electrons from the s state to the p or d state for hcp, fcc, and bcc crystals of Co and Rh increases with the elemental period number to form a stronger cohesion, a higher cohesive energy, or a more stable lattice between atoms in heavier metals.展开更多
Using first-principles density functional calculations, lattice stability of γ-Ni under [001], [110], and [111] uniaxial tensions and the effect of alloying elements Co and Re on the uniaxial tensile behavior of γ-N...Using first-principles density functional calculations, lattice stability of γ-Ni under [001], [110], and [111] uniaxial tensions and the effect of alloying elements Co and Re on the uniaxial tensile behavior of γ-Ni were studied in this paper.With elastic constants and phonon spectra calculations, we examined the mechanical stability and phonon stability of Ni during the uniaxial tensions along the three characteristic directions. The results show that the mechanical stability and phonon stability of a lattice occurs before the maximum stress–strain point under the [001] and [111] tension, respectively.The effects of Co and Re on the ideal tensile strength of γ-Ni show a significant directivity: Co and Re have little effect on the stresses in [001] and [111] directions, but increases the ideal strength of the system in the weakest uniaxial tensile direction. Moreover, the strengthening effect of Re is significantly better than that of Co. By further analyzing electronic structure, it is found that the effect of alloying elements on the uniaxial tensile behavior of γ-Ni comes from their interactions with host atoms.展开更多
The effects of high pressure on lattice stability, mechanical and thermodynamic properties of L1_2 structure Al_3Tm and Al_3Lu are studied by first-principles calculations within the VASP code. The phonon dispersion c...The effects of high pressure on lattice stability, mechanical and thermodynamic properties of L1_2 structure Al_3Tm and Al_3Lu are studied by first-principles calculations within the VASP code. The phonon dispersion curves and density of phonon states are calculated by using the PHONONPY code. Our results agree well with the available experimental and theoretical values. The vibrational properties indicate that Al_3Tm and A_3Lu keep their dynamical stabilities in L1_2 structure up to 100 GPa. The elastic properties and Debye temperatures for Al_3Tm and Al_3 Lu increase with the increase of pressure. The mechanical anisotropic properties are discussed by using anisotropic indices AG, AU, AZ, and the threedimensional(3D) curved surface of Young's modulus. The calculated results show that Al_3Tm and Al_3Lu are both isotropic at 0 GPa and anisotropic under high pressure. In the present work, the sound velocities in different directions for Al_3Tm and Al_3Lu are also predicted under high pressure. We also calculate the thermodynamic properties and provide the relationships between thermal parameters and temperature/pressure. These results can provide theoretical support for further experimental work and industrial applications.展开更多
Ab initio energetic calculations based on the density functional theory (DFF) and the projector augmented wave method (PAW) for determining the polymorphisms of lanthanide sesquioxides Ln2O3 (where Ln = rare-eart...Ab initio energetic calculations based on the density functional theory (DFF) and the projector augmented wave method (PAW) for determining the polymorphisms of lanthanide sesquioxides Ln2O3 (where Ln = rare-earth element, Y, and Sc), LnMO3 perovskites (where M = AI and Ga), and Ln2B207 pyrochlores (where B = Ti, Zr, and Hf) were reported. The relative lattice stabilities agreed well with the critically assessed results or the experimental results except the C-type Ln2O3 with a cubic structure, for which the calculated total energies were considerably more negative. With the increase of the Ln^3+-cation radius, the polymorphic structures showed a degenerative tendency. The tendencies and quantities of the enthalpies of formation of the ternary oxide ceramics synthesized from their constituent binary oxides reasonably agreed with the available experimental results, and valuable thermodynamic properties were afforded to the compound, for which no experimental data is available. The enthalpies of formation of both perovskites and pyrochlores tend to become more negative with the increase of the Ln^3+-cation radius.展开更多
Group IVB carbides have been applied in extreme aerospace environments as hard ceramic coatings; ZrC is being considered as a replacement for SiC in nuclear reactors. Therefore, a thorough understanding of the laser i...Group IVB carbides have been applied in extreme aerospace environments as hard ceramic coatings; ZrC is being considered as a replacement for SiC in nuclear reactors. Therefore, a thorough understanding of the laser irradiation response of group IVB carbides is of clear significance. However, the existing knowledge on the fundamental properties of IVB group carbides is limited and insufficient with regard to both irradiated and non-irradiated characteristics. We investigate the effect of ultrafast laser irradiation on the lattice stability of ceramic materials (IVB group carbides) using the density functional perturbation theory (DFPT). The calculated phonon frequencies of TiC and ZrC at the ground state are in good agreement with previous calculations and experimental values. The phonon frequencies of IVB group carbides are positive, even though the electronic temperature reached 5 eV. Thus, IVB group carbides are more stable under ultrafast laser irradiation, which has greater benefits in nuclear and aeronautical applications compared to metals (W, Na), semimetals (Bi), and semiconductors (Si, SIC). The thermodynamic properties of ZrC are calculated as functions of their lattice temperature at different electronic temperatures. The elastic shear constants of IVB group carbides satisfy the Born stability criteria at Te = 5 eV. In addition, a comparison of the predicted melting temperatures of IVB group carbides, reveal that HfC is better suited for extreme high-temperature environments.展开更多
Ab initio calculations of lattice constants, lattice stabilities of HgX(X = S, Se, Te) at different electronic temperatures(T_e) have been performed within the density functional theory(DFT). We find that the la...Ab initio calculations of lattice constants, lattice stabilities of HgX(X = S, Se, Te) at different electronic temperatures(T_e) have been performed within the density functional theory(DFT). We find that the lattice constants of HgX increase and the phonon frequencies reduce as T_e increases. Especially the transverse-acoustic(TA) phonon frequencies of HgX gradually become negative with the elevation of the electron temperature. That is to say ultrafast intense laser induces lattice instabilities of HgX and athermal melting appears for the increase of laser intensity. What is more, with the X atom number increasing, the critical electronic temperatures of HgX are decreased in sequence. This result would be helpful for understanding the athermal melting processes for femtosecond laser micromachining.展开更多
Developing a universal and reliable strategy for the modulation of composition and structure of energy storage materials with stable cycling performance is vital for hydrogen and its isotopes storage advanced system,y...Developing a universal and reliable strategy for the modulation of composition and structure of energy storage materials with stable cycling performance is vital for hydrogen and its isotopes storage advanced system,yet still challenging.Herein,an ultra-stable lattice structure is designed and verified to increase atomic chaos and interference for effectively inhibiting disproportionation reaction and improving cycling stability in ZrCo-based hydrogen isotopes storage alloy.After screening in terms of configuration entropy calculation,we construct Zr_(1-2)Nb_(x)Co_(1-2x)Cu_(x)Ni_(x)(x=0.15,0.2,0.25) alloys with increased atomic chaos,and successfully achieve stable isostructural de-/hydrogenation during 100 cycles,whose cycling capacity retentions are above 99%,much higher than 22.4%of pristine ZrCo alloy.Both theoretical analysis and experimental evidences indicate the high thermo-stability of orthorhombic lattice in Zr_(0.8)Nb_(0.2)Co_(0.6)Cu_(0.2)Ni_(0.2) alloy.Notably,the increased atomic chaos and interference in Zr_(0.8)Nb_(0.2)Co_(0.6)Cu_(0.2)Ni_(0.2) alloy causes regulation in hydrogen local chemical neighborhood,thereby confusing the hydrogen release order,which effectively eliminates lattice distortion and unlocks an ultrastable lattice structure.This study provides a new and comprehensive inspiration for hydrogen atoms transport behaviors and intrinsic reason of stable orthorhombic transformation,which can contribute to paving the way for other energy storage materials modulation.展开更多
In this study, the changing trend of crystal-lattice constant and the influential factors of the stability of supersaturated solid solutions with various alloying additions in the Al–X(Zn, Mg, Cu) binary alloys wer...In this study, the changing trend of crystal-lattice constant and the influential factors of the stability of supersaturated solid solutions with various alloying additions in the Al–X(Zn, Mg, Cu) binary alloys were investigated. The samples were analyzed using X-ray diffraction(XRD),X-ray absorption fine structure(XAFS), and scanning electron microscope(SEM). It is found that the addition of Cu causes the largest change of crystal-lattice constant of the Al–xCu supersaturated solid solution binary alloy. The most dramatic change occurs in the initial stage of Cu addition.The change is stabilized thereafter. Also, at the same alloying element addition to the Al–X(X = Zn, Mg, Cu)binary alloys, the Al–xCu is the most unstable system.Influential factors of the stability include the lattice constant change and the type of alloying element. The larger the lattice constant changes, the more unstable the supersaturated solid solution is. The alloying element, easy to aggregate, often leads to the solid solution less stable.展开更多
基金supported by the Doctoral Discipline Foundation of the Ministry of Education of China (No. 20070533118)the National Natural Science Foundation of China (No. 50871124)the Postdoctoral Foundation of Central South University
文摘Lattice constants, total energies, and densities of state of transition metals Co, Rh, and Ir in the VⅢB group with different crystalline structures were calculated via generalized gradient approximation (GGA) of the total energy plane wave pseudopotential method in first-principles. The lattice stabilities of Rh and Ir are ΔG^ bcc-hcp 〉 Δ G^fcc-hcp 〉 0, agreeing well with those of the projector augmented wave method in first-principles and the CALPHAD method in spite of elemental Co. Analyses of the electronic structures to lattice stability show that crystalline Rh and Ir with fcc structures have the obvious characteristic of a stable phase, agreeing with the results of total energy calculations. Analyses of atomic populations show that the transition rate of electrons from the s state to the p or d state for hcp, fcc, and bcc crystals of Co and Rh increases with the elemental period number to form a stronger cohesion, a higher cohesive energy, or a more stable lattice between atoms in heavier metals.
基金Project supported by Beijing Municipality Science and Technology Commission,China(Grant No.D161100002416001)the National Key R&D Program of China(Grant No.2017YFB0701502)
文摘Using first-principles density functional calculations, lattice stability of γ-Ni under [001], [110], and [111] uniaxial tensions and the effect of alloying elements Co and Re on the uniaxial tensile behavior of γ-Ni were studied in this paper.With elastic constants and phonon spectra calculations, we examined the mechanical stability and phonon stability of Ni during the uniaxial tensions along the three characteristic directions. The results show that the mechanical stability and phonon stability of a lattice occurs before the maximum stress–strain point under the [001] and [111] tension, respectively.The effects of Co and Re on the ideal tensile strength of γ-Ni show a significant directivity: Co and Re have little effect on the stresses in [001] and [111] directions, but increases the ideal strength of the system in the weakest uniaxial tensile direction. Moreover, the strengthening effect of Re is significantly better than that of Co. By further analyzing electronic structure, it is found that the effect of alloying elements on the uniaxial tensile behavior of γ-Ni comes from their interactions with host atoms.
基金Project supported by the Scientific Technology Plan of the Educational Department of Liaoning Province and Liaoning Innovative Research Team in University,China(Grant No.LT2014004)the Program for the Young Teacher Cultivation Fund of Shenyang University of Technology,China(Grant No.005612)
文摘The effects of high pressure on lattice stability, mechanical and thermodynamic properties of L1_2 structure Al_3Tm and Al_3Lu are studied by first-principles calculations within the VASP code. The phonon dispersion curves and density of phonon states are calculated by using the PHONONPY code. Our results agree well with the available experimental and theoretical values. The vibrational properties indicate that Al_3Tm and A_3Lu keep their dynamical stabilities in L1_2 structure up to 100 GPa. The elastic properties and Debye temperatures for Al_3Tm and Al_3 Lu increase with the increase of pressure. The mechanical anisotropic properties are discussed by using anisotropic indices AG, AU, AZ, and the threedimensional(3D) curved surface of Young's modulus. The calculated results show that Al_3Tm and Al_3Lu are both isotropic at 0 GPa and anisotropic under high pressure. In the present work, the sound velocities in different directions for Al_3Tm and Al_3Lu are also predicted under high pressure. We also calculate the thermodynamic properties and provide the relationships between thermal parameters and temperature/pressure. These results can provide theoretical support for further experimental work and industrial applications.
文摘Ab initio energetic calculations based on the density functional theory (DFF) and the projector augmented wave method (PAW) for determining the polymorphisms of lanthanide sesquioxides Ln2O3 (where Ln = rare-earth element, Y, and Sc), LnMO3 perovskites (where M = AI and Ga), and Ln2B207 pyrochlores (where B = Ti, Zr, and Hf) were reported. The relative lattice stabilities agreed well with the critically assessed results or the experimental results except the C-type Ln2O3 with a cubic structure, for which the calculated total energies were considerably more negative. With the increase of the Ln^3+-cation radius, the polymorphic structures showed a degenerative tendency. The tendencies and quantities of the enthalpies of formation of the ternary oxide ceramics synthesized from their constituent binary oxides reasonably agreed with the available experimental results, and valuable thermodynamic properties were afforded to the compound, for which no experimental data is available. The enthalpies of formation of both perovskites and pyrochlores tend to become more negative with the increase of the Ln^3+-cation radius.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11474207 and 11374217)
文摘Group IVB carbides have been applied in extreme aerospace environments as hard ceramic coatings; ZrC is being considered as a replacement for SiC in nuclear reactors. Therefore, a thorough understanding of the laser irradiation response of group IVB carbides is of clear significance. However, the existing knowledge on the fundamental properties of IVB group carbides is limited and insufficient with regard to both irradiated and non-irradiated characteristics. We investigate the effect of ultrafast laser irradiation on the lattice stability of ceramic materials (IVB group carbides) using the density functional perturbation theory (DFPT). The calculated phonon frequencies of TiC and ZrC at the ground state are in good agreement with previous calculations and experimental values. The phonon frequencies of IVB group carbides are positive, even though the electronic temperature reached 5 eV. Thus, IVB group carbides are more stable under ultrafast laser irradiation, which has greater benefits in nuclear and aeronautical applications compared to metals (W, Na), semimetals (Bi), and semiconductors (Si, SIC). The thermodynamic properties of ZrC are calculated as functions of their lattice temperature at different electronic temperatures. The elastic shear constants of IVB group carbides satisfy the Born stability criteria at Te = 5 eV. In addition, a comparison of the predicted melting temperatures of IVB group carbides, reveal that HfC is better suited for extreme high-temperature environments.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11374217 and 11176020)
文摘Ab initio calculations of lattice constants, lattice stabilities of HgX(X = S, Se, Te) at different electronic temperatures(T_e) have been performed within the density functional theory(DFT). We find that the lattice constants of HgX increase and the phonon frequencies reduce as T_e increases. Especially the transverse-acoustic(TA) phonon frequencies of HgX gradually become negative with the elevation of the electron temperature. That is to say ultrafast intense laser induces lattice instabilities of HgX and athermal melting appears for the increase of laser intensity. What is more, with the X atom number increasing, the critical electronic temperatures of HgX are decreased in sequence. This result would be helpful for understanding the athermal melting processes for femtosecond laser micromachining.
基金financial supports from the National Natural Science Foundation of China (52071286, U2030208 and 51901213)the National Key Research and Development Program of China (2017YFE0301505)。
文摘Developing a universal and reliable strategy for the modulation of composition and structure of energy storage materials with stable cycling performance is vital for hydrogen and its isotopes storage advanced system,yet still challenging.Herein,an ultra-stable lattice structure is designed and verified to increase atomic chaos and interference for effectively inhibiting disproportionation reaction and improving cycling stability in ZrCo-based hydrogen isotopes storage alloy.After screening in terms of configuration entropy calculation,we construct Zr_(1-2)Nb_(x)Co_(1-2x)Cu_(x)Ni_(x)(x=0.15,0.2,0.25) alloys with increased atomic chaos,and successfully achieve stable isostructural de-/hydrogenation during 100 cycles,whose cycling capacity retentions are above 99%,much higher than 22.4%of pristine ZrCo alloy.Both theoretical analysis and experimental evidences indicate the high thermo-stability of orthorhombic lattice in Zr_(0.8)Nb_(0.2)Co_(0.6)Cu_(0.2)Ni_(0.2) alloy.Notably,the increased atomic chaos and interference in Zr_(0.8)Nb_(0.2)Co_(0.6)Cu_(0.2)Ni_(0.2) alloy causes regulation in hydrogen local chemical neighborhood,thereby confusing the hydrogen release order,which effectively eliminates lattice distortion and unlocks an ultrastable lattice structure.This study provides a new and comprehensive inspiration for hydrogen atoms transport behaviors and intrinsic reason of stable orthorhombic transformation,which can contribute to paving the way for other energy storage materials modulation.
基金financially supported by the National Natural Science Foundation of China (No. 51274046)
文摘In this study, the changing trend of crystal-lattice constant and the influential factors of the stability of supersaturated solid solutions with various alloying additions in the Al–X(Zn, Mg, Cu) binary alloys were investigated. The samples were analyzed using X-ray diffraction(XRD),X-ray absorption fine structure(XAFS), and scanning electron microscope(SEM). It is found that the addition of Cu causes the largest change of crystal-lattice constant of the Al–xCu supersaturated solid solution binary alloy. The most dramatic change occurs in the initial stage of Cu addition.The change is stabilized thereafter. Also, at the same alloying element addition to the Al–X(X = Zn, Mg, Cu)binary alloys, the Al–xCu is the most unstable system.Influential factors of the stability include the lattice constant change and the type of alloying element. The larger the lattice constant changes, the more unstable the supersaturated solid solution is. The alloying element, easy to aggregate, often leads to the solid solution less stable.