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1.
Using ab initio calculations, we have studied the structural, electronic and elastic properties of M2SC, with M = Ti, Zr and Hf. Geometrical optimization of the unit cell are in good agreement with the available experimental data. The band structures show that all three materials are conducting. The analysis of the site and momentum projected densities shows that the bonding is achieved through a hybridization of M-atom d states with S and C-atom p states. The Md-Sp bonds are lower in energy and are stiffer than Md-Cp bonds. The elastic constants are calculated using the static finite strain technique. We derived the bulk and shear moduli, Young's moduli and Poisson's ratio for ideal polycrystalline M2SC aggregates. We estimated the Debye temperature of M2SC from the average sound velocity. This is a quantitative theoretical prediction of the elastic properties of Ti2SC, Zr2SC, and Hf2SC compounds, and it still awaits experimental confirmation. 相似文献
2.
A. Bouhemadou 《Applied Physics A: Materials Science & Processing》2009,96(4):959-967
Using ab initio calculations, we have studied the structural, electronic and elastic properties of M2GeC, with M=Ti, V, Cr, Zr, Nb, Mo, Hf, Ta and W. Geometrical optimizations of the unit cell are in agreement with the available
experimental data. The band structures show that all studied materials are electrical conductors. The analysis of the site
and momentum projected densities shows that bonding is due to M d-C p and M d-Ge p hybridizations. The elastic constants are calculated using the static finite strain technique. The shear modulus C
44, which is directly related to the hardness, reaches its maximum when the valence electron concentration is in the range 8.41–8.50.
We derived the bulk and shear moduli, Young’s moduli and Poisson’s ratio for ideal polycrystalline M2GeC aggregates. We estimated the Debye temperature of M2GeC from the average sound velocity. This is the first quantitative theoretical prediction of the elastic constants of Ti2GeC, V2GeC, Cr2GeC, Zr2GeC, Nb2GeC, Mo2GeC, Hf2GeC, Ta2GeC and W2GeC compounds, and it still awaits experimental confirmation. 相似文献
3.
M2AlC phases, where M is a transition metal, are layered ternary compounds that possess unusual properties. In this paper, we have calculated the elastic properties of M2AlC, with M=Ti, V, Cr, Nb and Ta, by means of ab initio total energy calculations using the projector augmented-wave method. We have derived the bulk and shear moduli, Young's moduli and Poisson's ratio for ideal polycrystalline M2AlC aggregates. We have estimated the elastic modulus of Cr2AlC with 357.7 GPa while the values of all other phases are in the range 309±10 GPa. We suggest that this can be understood based on the calculated bond energies for the M-C bonds. Furthermore, our results indicate a profound elastic anisotropy of M2AlC even compared to materials with a well-established anisotropic character such as α-alumina. Finally, we have estimated the Debye temperatures of M2AlC from the average sound velocity. 相似文献
4.
First principle calculations of elastic properties under pressure of the filled tetrahedral semiconductors LiZnN, LiZnP and LiZnAs are presented, using the pseudo-potential plane-waves approach based on density functional theory, within the local density approximation. Elastic constants, bulk modulus, Young’s modulus and Poisson’s ratio are calculated at zero pressure. A linear dependence of the bulk modulus and elastic constants with applied pressure is found. As the experimental elastic constants are not available for LiZnX, we have also calculated the elastic constants of GaN, GaP and GaAs, the binary analogues of LiZnN, LiZnP and LiZnAs, respectively, for checking the reliability and accuracy of our predicted results for LiZnX. The obtained results agree well with the available experimental data. 相似文献
5.
Using first-principles density functional calculations, the effect of high pressures, up to 40 GPa, on the structural and elastic properties of ANCa3, with A = P, As, Sb, and Bi, were studied by means of the pseudo-potential plane-waves method. Calculations were performed within the local density approximation and the generalized gradient approximation for exchange-correlation effects. The lattice constants are in good agreement with the available results. The elastic constants and their pressure dependence are calculated using the static finite strain technique. We derived the bulk and shear moduli, Young's modulus, Poisson's ratio and Lamé's constants for ideal polycrystalline ANCa3 aggregates. By analysing the ratio between the bulk and shear moduli, we conclude that ANCa3 compounds are brittle in nature. We estimated the Debye temperature of ANCa3 from the average sound velocity. This is the first quantitative theoretical prediction of the elastic properties of PNCa3, AsNCa3, SbNCa3, and BiNCa3 compounds, and it still awaits experimental confirmation. 相似文献
6.
A. Bouhemadou R. Khenata M. Chegaar 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,56(3):209-215
Using first-principles density functional calculations, the effect of high
pressures, up to 20 GPa, on the structural and elastic properties of
Zr2AlX and Ti2AlX, with X = C and N, were studied by means of the
pseudo-potential plane-waves method. Calculations were performed within the
local density approximation to the exchange-correlation approximation
energy. The lattice constants and the internal parameters are in agreement
with the available results. The elastic constants and their pressure
dependence are calculated using the static finite strain technique. We
derived the bulk and shear moduli, Young's moduli and Poisson's ratio for
ideal polycrystalline Zr2AlX and Ti2AlX aggregates. We estimated
the Debye temperature of Zr2AlX and Ti2AlX from the average sound
velocity. This is the first quantitative theoretical prediction of the
elastic properties of Zr2AlC, Zr2AlN and Ti2AlN compounds,
and it still awaits experimental confirmation. 相似文献
7.
Elastic properties of TaC have been investigated experimentally and by model calculations. The elastic stiffness coefficients c11=597(11) GPa and c44=153(2) GPa were determined on a (100)-oriented disc-shaped monocrystal at room temperature using a plane-wave ultrasound method. The corresponding theoretical values (c11=621(3), c44=166.8(3) GPa) agree within 4 and 8%, respectively. Therefore, we are confident that the predicted value for c12 is equally accurate, and this allows the prediction of the Bulk and Young's moduli and the Poisson ratio. Data published earlier are critically reviewed and predictions concerning the possibility to synthesize extremely incompressible carbides are made. 相似文献
8.
We have investigated structural and elastic properties of PtN2 under high pressures using norm-conserving pseudopotentials within the local density approximation (LDA) in the frame of density-functional theory. Calculated results of PtN2 are in agreement with experimental and available theoretical values. The a/a0, V/V0, ductility/brittleness, elastic constants Cij, shear modulus C′, bulk modulus B, shear modulus G, Young's modulus E, Poisson's ratio σ and anisotropy factor A as a function of applied pressure are presented. Through the quasi-harmonic Debye model, we also study thermodynamic properties of PtN2. The thermal expansion versus temperature and pressure, thermodynamic parameters X (X=Debye temperature or specific heat) with varying pressure P, and heat capacity of PtN2 at various pressures and temperatures are estimated. 相似文献
9.
First-principles calculations have been performed on the face-centered cubic (FCC) magnesium-transition metal (TM) hydrides Mg7TMH16 (TM=Sc, Ti, V, Y, Zr, Nb). The cohesive energies are calculated to analyze the stability, and the obtained enthalpies of formation for hydrides Mg7TMH16 have been used to investigate the possible pathways of formation reaction. The calculated enthalpy changes show that the decomposition temperatures of Mg7TMH16 are lower than that of MgH2. The electronic densities of states reveal that all the hydrides studied here exhibit metallic characteristics. The bonding nature of Mg7TMH16 is investigated, showing stronger covalent bonding between TM and H than between Mg and H. 相似文献
10.
Dependence of elastic properties on temperature for rutile TiO2 is investigated by the Cambridge Serial Total Energy Package (CASTEP) program in the frame of density function theory (DFT) and the quasi-harmonic Debye model The six independent elastlc constants of rutile TiO2 at high temperature are theoretically obtained for the first time. It is found that with increasing temperature, the elastic constants will decrease monotonically. Moreover, we successfully obtain the polycrystalline moduli BH and GH, as well as the Debye temperature ⊙D. 相似文献
11.
The structure, elastic properties and elastic anisotropy of orthorhombic OsB2 are investigated by density functional theory method with the ultrasoft pseudopotential scheme in the frame of the generalized gradient approximation (GGA) as well as local density approximation (LDA). The obtained structural parameters, elastic constants, elastic anisotropy and Debye temperature for OsB2 under pressure are consistent with the available experimental data and other theoretical results. It is found that the elastic constants, bulk modulus and Debye temperature of OsB2 tend to increase with increasing pressure. It is predicted that OsB2 is not a superhard material from our calculations. 相似文献
12.
Bulk modulus and its pressure derivatives of cuprous halides 总被引:1,自引:0,他引:1
The ab initio pseudopotential approach to the total crystal energy is presented using local DF formalism. The expressions for bulk modulus, its first and second pressure derivatives for group I-VII semiconductor binary compounds are derived. The expression for the second pressure derivative of the bulk modulus for four-fold crystal structures is derived for the first time within the pseudopotential framework. The computed results of the bulk modulus for cuprous halides are very close to the available experimental data. 相似文献
13.
Oxygen vacancy pairs have been suggested to play a role in the reduction of NO molecules on ceria and for the oxidation processes of reducible rare-earth oxides. The formation energy of the oxygen vacancy pairs and the changes in the structural and electronic properties of the ceria (110) surface with oxygen vacancy pairs are investigated using density-functional theory (DFT + U) methodology within the generalized gradient approximation. It is found that the excess electrons localize on the Ce ions neighbouring the vacancies, and the most stable structure for the oxygen vacancy pairs on the ceria (110) surface is at next-nearest-neighbour site. 相似文献
14.
The elastic constants and thermodynamic properties of Li2O for high temperatures and pressures are calculated by the ab initio unrestricted Hartree-Fock (HF) linear combination of atomic orbital (LCAO) periodic approach. The lattice constant, elastic constants, Debye temperature, and thermal expansion coefficient obtained are in good agreement with the available experimental data and other theoretical results. It is found that at zero pressure the elastic constants C11, C12 and C44, bulk modulus B and Debye temperature ΘD decrease monotonically over the wide range of temperatures from 0 to 1100 K. When the temperature , C12 approaches zero, consistently with the transition temperature 1200 K. However, with increasing pressure, they all increase monotonically and the anisotropy will weaken. 相似文献
15.
First-principles calculations of the crystal structure and the elastic properties of RuB2 have been carried out with the plane-wave pseudopotential density functional theory method. The calculated values are in very good agreement with experimental data as well as with some of the existing model calculations. The elastic constants cij, the aggregate elastic moduli (B, G, E), Poisson's ratio, and the elastic anisotropy with pressure have been investigated. Through the quasi-harmonic Debye model considering the phonon effects, the isothermal bulk modulus, the thermal expansions, Grüneisen parameters, and Debye temperatures depending on the temperature and pressure are obtained in the whole pressure range from 0 to 60 GPa and temperature range from 0 to 1100 K as well as compared to available data. 相似文献
16.
The structural parameters, elastic, electronic, and optical properties of hexagonal BiAlO3 were investigated by the density functional theory. The calculated structural parameters are in good agreement with previous calculation and experimental data. The structural stability of BiAlO3 has been confirmed by calculation of the elastic constants. The energy band structure, density of states, and Mulliken charge populations were obtained. BiAlO3 presents an indirect band gap of 3.28 eV. Furthermore, the optical properties were calculated and analyzed. It is shown that BiAlO3 is a promising dielectric material. 相似文献
17.
A theoretical study of structural, electronic and optical properties of cubic BaTiO3 and BaZrO3 perovskites is presented, using the full-potential linear augmented plane wave (FP-LAPW) method as implemented in the WIEN2K code. In this approach the local density approximation (LDA) is used for the exchange-correlation (XC) potential. Results are given for lattice constant, bulk modulus, its pressure derivative, band structure, density of states, pressure coefficients of energy gaps and refractive indices. The results are compared with previous calculations and experimental data. 相似文献
18.
Structural, elastic and electronic properties of ReO2 are investigated by first-principles calculations based on density functional theory. The ground stateof ReO2 has an orthorhombic symmetry which belongs to space group Pbcn with a=4.7868Å b=5.5736Å, and c=4.5322Å. The calculated bulk moduli are 322GPa, 353GPa, and 345GPa for orthorhombic, tetragonal, and monoclinic ReO2, respectively, indicating that ReO2 has a strong incompressibility. ReO2 is a metal ductile solid and presents large elastic anisotropy. The obtained Debye temperatures are 850K for orthorhombic, 785K for tetragonal, and 791K for monoclinic ReO2. 相似文献
19.
First principles study of structural, elastic, electronic and optical properties of the cubic perovskite-type BaHfO3 has been reported using the pseudo-potential plane wave method within the local density approximation. The calculated equilibrium lattice is in a reasonable agreement with the available experimental data. The elastic constants and their pressure dependence are calculated using the static finite strain technique. A linear pressure dependence of the elastic stiffnesses is found. Band structures show that BaHfO3 is a direct band gap between the occupied O 2p and unoccupied Hf d states. The variation of the gap versus pressure is well fitted to a quadratic function. Furthermore, in order to understand the optical properties of BaHfO3, the dielectric function, absorption coefficient, optical reflectivity, refractive index, extinction coefficient, and electron energy loss are calculated for radiation up to 30 eV. We have found that O 2p states and Hf 5d states play a major role in the optical transitions as initial and final states, respectively. This is the first quantitative theoretical prediction of the elastic, electronic and optical properties of BaHfO3 compound, and it still awaits experimental confirmation. 相似文献
20.
The five different elastic constants of the superconducting NbB2 are calculated for the first time by ab initio density functional method with both correlation and exchange potentials. In the absence of experimental data, the results are compared with those of other related diborides. The fully relaxed and isotropic bulk moduli are also estimated and the implication of their comparison is made. 相似文献