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1.
《Intermetallics》2014
To improve the performance of a thermoelectric material CuGaTe2, element Ag is doped to replace element Ga and we investigate the electronic structure, phase stability, elastic and thermoelectric properties of CuGa1−xAgxTe2 (x = 0, 0.25 and 0.5) via first-principles method. The phase stability of CuGa1−xAgxTe2 is discussed by analyzing the formation energy, cohesive energy and elastic constants. The calculated sound velocities decrease with the increase of Ag content, which is favorable for reducing the lattice thermal conductivity. The analysis of band structures shows that the replacement of Ga by Ag makes CuGaTe2 undergo a direct-indirect semiconductor transition. The Ag doping induces steep density of states in valence band edge, which is beneficial for increasing the carrier concentration and improving thermoelectric performance of CuGaTe2. 相似文献
2.
《Intermetallics》2014
Three competing structures (C11b, C16 and E93) of intermetallic Zr2Cu have been systematically investigated by first-principles calculations and quasi-harmonic Debye model. Both the calculated equation of states (EOS) and pressure–enthalpy results indicate a structural phase transition from C11b to C16 phase at around 11–14 GPa. The calculated equilibrium crystal parameters and elastic constants are in consistence with available experimental or theoretical data. All three phases are mechanically stable according to the elastic stability criteria, and ductile according to Pugh's ratio, while the ambient-stable C11b phase shows a higher elastic anisotropy. Furthermore, differences in the nature of bonding between three competing structures are uncovered by electron density topological analysis. C11b Zr2Cu possesses an intriguing pseudo BaFe2As2-type structure with the charge density maxima at Zr tetrahedral interstices serving as Fe-position pseudoatoms; C16 Zr2Cu contains Zr-pair configurations bonded through bifurcated Zr–Zr bonding paths; while the E93 phase has only conventional straight bonding. Additionally, through quasi-harmonic Debye model, the pressure and temperature dependences of the bulk modulus, specific heat, Debye temperature, Grüneisen parameter and thermal expansion coefficient for three phases are obtained and discussed. 相似文献
3.
《Intermetallics》2014
Effect of tetragonal distortion on the electronic structure, dynamical properties and superconductivity in Mo3Sb7 is analyzed using first principles electronic structure and phonon calculations. Rigid muffin tin approximation (RMTA) and McMillan formulas are used to calculate the electron–phonon coupling constant λ and superconducting critical temperature. Our results show, that tetragonal distortion has small, but beneficial effect on superconductivity, slightly increasing λ, and the conclusion that the electron–phonon mechanism is responsible for the superconductivity in Mo3Sb7 is supported. The spin-polarized calculations for the ordered (ferromagnetic or antiferromagnetic), as well as disordered (disordered local moment) magnetic states yielded non-magnetic ground state. We point out that due to its experimentally observed magnetic properties the tetragonal Mo3Sb7 might be treated as noncentrosymmetric superconductor, which could have influence for the pairing symmetry. In this context the relativistic band structure is calculated and spin–orbit interaction effects are discussed. 相似文献
4.
《Intermetallics》2014
A systematic investigation on structural, elastic and electronic properties of Rh–Zr intermetallic compounds is conducted using first-principles electronic structure total energy calculations. The equilibrium lattice parameters, enthalpies of formation (Efor), cohesive energies (Ecoh) and elastic constants are presented. Of the eleven considered candidate structures, Rh4Zr3 is most stable with the lowest Efor. The two orthogonal-type, relative to the CsCl-type, are the competing ground-state structures of RhZr. The result is in agreement with the experimental reports in the literature. The analysis of Efor and mechanical stability excludes the presence of Rh2Zr and RhZr4 at low temperature mentioned by .Curtarolo et al. [Calphad 29, 163 (2005)]. It is found that the bulk modulus B increases monotonously with Rh concentration, whereas all other quantities (shear modulus G, Young's modulus E, Poisson's ratio σ and ductility measured by B/G) show nonmonotonic variation. RhZr2 exhibits the smallest shear/Young's modulus, the largest Poisson's ratio and ductility. Our results also indicate that all the Rh–Zr compounds considered are ductile. Furthermore, the detailed electronic structure analysis is implemented to understand the essence of stability. 相似文献
5.
《Intermetallics》2014
The structural, elastic, thermodynamic and electronic properties of L12-ordered intermetallic compounds Ni3X (X = Al, Ga and Ge) under pressure range from 0 to 50 GPa with a step of 10 GPa have been investigated using first-principles method based on density functional theory (DFT). The calculated structural parameters of Ni3X at zero pressure and zero temperature are consistent with the experimental data. The results of bulk modulus B, shear modulus G, Young's modulus E, Poisson's ratio v, anisotropy index AU and Debye temperature ΘD increase with the increase of external pressure. In addition, the Debye temperature of these compounds gradually reduce as the order of Ni3Al > Ni3Ga > Ni3Ge. The ratio of shear modulus to bulk modulus G/B shows that the three binary compounds are ductile materials, and the ductility of Ni3Al and Ni3Ga can be improved with pressure going up, while Ni3Ge is opposite. Finally, the pressure-dependent behavior of density of states, Mulliken charge and bond length are analyzed to explore the physical origin of the pressure effect on the structural, elastic and thermodynamic properties of Ni3X. 相似文献
6.
《Intermetallics》2014
The structural, electronic and elastic properties of four RuX (X = Sc, Ti, V and Zr) intermetallic compounds have been investigated by using density functional theory within full potential linearized augmented plane wave method and using generalized gradient approximations in the scheme of Perdew, Burke and Ernzrhof (PBE), Wu and Cohen (WC) and Perdew et al. (PBEsol) for the exchange correlation potential. The relative phase stability in terms of volume-energy and enthalpy-pressure for these compounds is presented for the first time in three different (B1, B2 and B3) structures. The total energy is computed as a function of volume and fitted to Birch equation of states to find the ground state properties such as lattice constant (a0), bulk modulus (B) and its pressure derivative (B′). It is found that the lattice parameters in B2-phase agree well with the existing experimental and previous theoretical results. The second order elastic constants (SOECs) are also predicted for the above compounds. All the four compounds show ductile behavior. The ductility of these compounds has been analyzed using Pugh's rule. From the plots of electronic density of states (DOS), it can be concluded that these intermetallic compounds are metallic in nature. 相似文献
7.
《Intermetallics》2014
The structural, elastic and thermodynamic properties of FeB, Fe2B, orthorhombic and tetrahedral Fe3B, FeB2 and FeB4 iron borides are investigated by first-principle calculations. The elastic constants and polycrystalline elastic moduli of Fe–B compounds are usually large especially for FeB2 and FeB4, whose maximum elastic constant exceeds 700 GPa. All of the six compounds are mechanically stable. The Vickers hardness of FeB2 is estimated to be 31.4 GPa. Fe2B and FeB2 are almost isotropic, while the other four compounds have certain degree of anisotropy. Thermodynamic properties of Fe–B compounds can be accurately predicted through quasi-harmonic approximation by taking the vibrational and electronic contributions into account. Orthorhombic Fe3B is more stable than tetrahedral one and the phase transition pressure is estimated to be 8.3 GPa. 相似文献
8.
The Brewer–Engel Theory is a model capable of predicting novel materials, used in the past in particular for quite stable intermetallics based on the reaction of metals with non-bonding d electron pairs combined with metals with empty d orbitals. In this paper are shown the calculation procedures for bonding energies of 1:2 transition metal aluminide compounds characterized by MgCu2 crystal structures. The model utilizes parameters that include crystal field effect, Hume-Rothery Rules, and a modified Born–Haber cycle to characterize covalent and ionic bonding contribution of alloys. Interactions between transition metals exhibit enhanced d-bonding, whereas interactions between transition metals and non-transition metals exhibit reduced d-bonding. From the bonding energies, the percentage ionicity factor is determined which is an indication of the stability of the intermetallic compound. 相似文献
9.
《Intermetallics》2014
Effects of Ni vacancy, Ni antisite in Al sublattice, Cr in Al sublattice, Pt in Ni sublattice on the second-order elastic constants (SOECs) and third-order elastic constants (TOECs) of the B2 NiAl have been investigated using the first-principles methods. Lattice constant and the SOECs of NiAl are in good agreement with the previous results. The brittle/ductile transition map based on Pugh ratio G/B and Cauchy pressure Pc shows that Ni antisite, Cr, Pt and pressure can improve the ductility of NiAl, respectively. Ni vacancy and lower pressure can enhance the Vickers hardness Hv of NiAl. The density of states (DOS) and the charge density difference are also used to analysis the effects of vacancy, Ni antisite, Cr and Pt on the mechanical properties of NiAl, and the results are in consistent with the transition map. 相似文献
10.
《Intermetallics》2014
Density functional theory and Boltzmann theory calculations of the electronic and thermoelectric properties of Mg2Si subjected to isotropic strains have been performed. The electrical conductivity, the Seebeck coefficient and the power factor have been evaluated at two temperatures (300 K and 900 K) and two charge carrier concentrations (1018 cm−3 and 1.2 × 1020 cm−3 electrons and holes). Up to 3% of both compressive and tensile strains have been applied to the material. From our results, we can highlight that a significant improvement of both the Seebeck coefficient (S) and the power factor (PF) is obtained at low temperature and moderate n-doping. The increase in S and PF amounts to 40% and 100%, respectively, compared to the unstrained Mg2Si. 相似文献
11.
The influence of structural, elastic properties, thermodynamics and electronic properties Al-Y alloy were investigated by using first-principles. The equilibrium lattice constant, elastic constants, and elastic modulus as calculated here agree with results of previous studies. Calculated results of bulk modulus B, shear modulus G, Young’s modulus E, Poisson’s ratio v and Debye temperature all increase as pressure increase, but the opposite is true for heat capacity cp. In addition, the Debye temperature for the phases reduces gradually as follows: Al2Y > Al3Y> AlY. Additionally, the G/B ratio indicates that AlY and Al3Y are ductile materials, while Al2Y is a brittle material, and that the ductility of AlY and Al3Y can be improved with increased pressure, while the brittleness of Al2Y does not improve with increased pressure. Finally, the paper presents and discusses calculations of density of states and charge populations as they are affected by pressure. 相似文献
12.
《Intermetallics》2014
The temperature-dependent structural properties and anisotropic thermal expansion coefficients of α-/β-Nb5Si3 phases have been determined by minimizing the non-equilibrium Gibbs free energy as functions of crystallographic deformations. The results indicate that the crystal anisotropy of α-Nb5Si3 phase is much more temperature dependence than that of β-Nb5Si3 phase. The total/partial density of states of α-/β-Nb5Si3 phases are discussed in detail to analyze their electronic hybridizations. It is demonstrated that the bonding of the two phases is mainly contributed from the hybridization between Nb-4d and Si-3p electronic states. The temperature-dependent mechanical properties of α-/β-Nb5Si3 phases are further investigated via the quasi-harmonic approximation method in coupling with continuum elasticity theory. The calculated single-crystalline and polycrystalline elasticity shows that both phases are mechanically stable and exhibit the intrinsic brittleness. The results also suggest that α-Nb5Si3 phase possesses a superior ability of compression resistance but an inferior ability of high-temperature resistance of mechanical properties than those of β-Nb5Si3 phase. The bonding features of α-/β-Nb5Si3 phases are discussed by means of charge density difference analysis in order to explain the difference of the temperature-dependent mechanical properties between the two phases. 相似文献
13.
《Intermetallics》2014
The structural, electronic, elastic, mechanical and thermal properties of the isostructural and isoelectronic nonmagnetic RESn3 (RE = Y, La and Ce) compounds, which crystallize in AuCu3-type structure, are studied using first principles density functional theory based on full potential linearized augmented plane wave (FP-LAPW) method. The calculations are carried out within PBE-GGA, WC-GGA and PBE-sol GGA for the exchange correlation potential. Our calculated ground state properties such as lattice constant (a0), bulk modulus (B) and its pressure derivative (B′) are in good agreement with the experimental and other available theoretical results. We first time predict the elastic constants for these compounds using different approximations of GGA. All these RESn3 compounds are found to be ductile in nature in accordance with Pugh's criteria. The computed electronic band structures and density of states show metallic character of these compounds. The elastic properties including Poisson's ratio (σ), Young's modulus (E), shear modulus (GH) and anisotropy factor (A) are also determined using the Voigt–Reuss–Hill (VRH) averaging scheme. The average sound velocities (vm), density (ρ) and Debye temperature (θD) of these RESn3 compounds are also estimated from the elastic constants. We first time report the variation of elastic constants, elastic moduli, Cauchy's pressure, sound velocities and Debye temperatures of these compounds as a function of pressure. 相似文献
14.
《Intermetallics》2014
We employ density functional theory (DFT) to calculate pressure dependences of selected thermodynamic, structural and elastic properties as well as electronic structure characteristics of equiatomic B2 FeTi. We predict ground-state single-crystalline Young's modulus and its two-dimensional counterpart, the area modulus, together with homogenized polycrystalline elastic parameters. Regarding the electronic structure of FeTi, we analyze the band structure and electronic density of states. Employing (i) an analytical dynamical matrix parametrized in terms of elastic constants and lattice parameters in combination with (ii) the quasiharmonic approximation we then obtained free energies, the thermal expansion coefficient, heat capacities at constant pressure and volume, as well as isothermal bulk moduli at finite temperatures. Experimental measurements of thermal expansion coefficient complement our theoretical investigation and confirm our theoretical predictions. It is worth mentioning that, as often detected in other intermetallics, some materials properties of FeTi strongly differ from the average of the corresponding values found in elemental Fe and Ti. These findings can have important implications for future materials design of new intermetallic materials. 相似文献
15.
N. Novakovi N. Ivanovi V. Koteski I. Radisavljevi J. Beloevi-avor B. Ceki 《Intermetallics》2006,14(12):1403-1410
In order to investigate Hf-TM (TM = Fe, Co, Rh, Ru) phase diagrams in the region of 50:50% atomic ratio, we performed ab initio Full-Potential Linearized Augmented Plane Waves calculations of the most stable Hf and TM elemental phases and HfTM compounds of the CsCl and CuAu structure types. The obtained electronic structures, cohesive energies and enthalpies of formation are discussed and compared to some of the existing models and available experimental data. The non-existing compound HfFe is found to be at least metastable, and the reason for its absence from the phase diagram is discussed. 相似文献
16.
《Intermetallics》2015
The phase stability and the elastic properties of Al–La binary system intermetallic compounds were thoroughly investigated using first-principles calculations. Firstly, the 0 K phase diagram for this system was calculated using the formation enthalpy convex hull construction, which indicates three metastable phases, namely Al4La (I4/mmm), Al4La (Imm2), and AlLa3 (Pm-3m). Then, the stability of Al11La3 was examined at temperatures lower than 1000 K compared with the two Al4La allotropes and the Al + Al2La two-phase equilibrium. The results demonstrate that the needlelike phase in Mg–Al–La based alloys should be indexed as Al11La3, which is thermodynamically stable, with no decomposition under aging. Thirdly, AlLa3 (Pm-3m) is more stable than AlLa3 (P63/mmc) at temperatures higher than approximately 590 K, which well agrees with the experimental results. Finally, the elastic properties and vibrational properties for the stable Al–La intermetallic phases were calculated in this work. 相似文献
17.
《Intermetallics》2014
Full-potential linearized augmented plane wave (FLAPW) method has been employed within the generalized gradient approximation (GGA) to investigate structural and elastic properties of YAg, CeAg, HoCu, LaAg, LaZn, LaMg compounds. The calculated ground state properties such as lattice constants, bulk Modulus and elastic constants agree well with the experiment. The ductility or brittleness of these intermetallic compounds is predicted. The calculated results indicate that LaAg is the most ductile amongst the present compounds. For HoCu and LaZn compounds, the mechanical properties and Debye temperature are predicted from calculated elastic constants. In addition, chemical bonding of these compounds has been investigated in the light of topological analysis approach based on the theory of atoms in molecules. 相似文献
18.
《Intermetallics》2014
The structural and elastic properties of ternary B2 RuAl-based alloys are studied using first-principles calculations. Single-crystal elastic constants, atomic volumes, transfer energies, and electronic densities for RuAl-TM are computed, considering all possible transition-metal solute species TM. Calculated elastic constants are used to compute values of some commonly considered elasticity parameters, such as bulk modulus, shear modulus, Yong's modulus, Pugh ratio, and Cauchy pressure. The present results suggest that the bulk modulus of RuAl-TM increase approximately linearly with increasing electron density. Calculated elastic properties are in favorable accord with available experimental and theoretical data. 相似文献
19.
《Intermetallics》2014
It has been suggested that intrinsic ductile versus brittle properties of alloys be connected with bonding characters in some sense while there is no much proof. In this investigation, 27Al isotropic metallic shifts of Al–Li solid solutions were measured by 27Al NMR spectroscopy. Previously observed anomalous elastic properties upon Li alloying were found to be closely related to 27Al metallic shifts which were associated with s electron density of states at the Fermi level on Al sites. This result is relevant for better understanding of electronic origin of solid solution strengthening mechanisms in Al–Li alloys from the point of view of electronic structure. 相似文献
20.
HASTELLOY B-2 alloy was found to exhibit environmental embrittlement when tested in air and hydrogen at ambient temperature after atomic ordering introduced by a heat treatment at 700 °C for 24 h. Molybdenum in the HASTELLOY B-2 alloy was probably reactive enough to dissociate water vapor in air to generate atomic hydrogen, resulting in hydrogen embrittlement. The percentage of transgranular fracture increased as the test environment changed from hydrogen gas to moist air or water vapor, and vacuum or oxygen. With the addition of 100 wt ppm B, the environmental embrittlement was completely eliminated, with the tensile properties independent of both test environment and strain rate. The fracture mode remained the same, i.e. ductile dimpling, after B-doping when tested in different environments. The immunity of the B-doped B2 alloy to environmental sensitivity remained even after long-term heat treatment. Auger analysis does not detect any boron segregation at the grain boundaries. The mechanism of boron doping in eliminating the environmental embrittlement in the Ni–Mo alloy is apparently different from that in many L12-type alloys such as Ni3Al and Ni3Si. 相似文献