Calculation Of Elastic Properties Research Articles

First principle calculations of elastic and thermodynamic properties of Ir3Nb and Ir3V with L12 structure under high pressure

The structural and elastic properties of the L12 structure Ir3Nb and Ir3V under pressure have been investigated by means of the first principles calculations based on the density functional theory within the generalized gradient approximation. The lattice parameters of Ir3Nb and Ir3V obtained by minimization of the total energy are consistent with the available experimental and other theoretical results. In addition, the elastic constants (C11, C12, C44) of Ir3Nb and Ir3V show that they are mechanical stable structures under pressure. The values of B/G exhibit an upward trend with increasing pressure, which means its ductility increased. When the pressure reaches 45 GPa, the Cauchy pressures and B/G values reveal that Ir3Nb and Ir3V change from brittle to ductile. Finally, through quasi-harmonic Debye model, the temperature and pressure dependences of thermodynamic properties are predicted in a wide pressure (0–50 GPa) and temperature (0–1200 K) ranges.

Calculation of lattice dynamics, elastic and dielectric properties of γ-BiB3O6 and δ-BiB3O6

The crystal lattice vibration frequencies, densities of phonon states, elastic moduli, and high-frequency permittivities have been calculated in terms of the density functional theory method for two polymorphs γ-BiB3O6 and δ-BiB3O6. Based on the calculated densities of phonon states, the temperature dependences of the free energies of two considered bismuth triborate modifications have been constructed, and the temperature of the phase transition between these modifications has been determined (1100 K). The structure of a possible nonpolar praphase of δ-BiB3O6 has been proposed. The polarization of δ-BiB3O6 has been estimated as 131 μC/cm2.

Effective elastic properties and stress states of doubly periodic array of inclusions with complex shapes by isogeometric boundary element method

Isogeometric analysis is a new numerical method that has received a lot of attentions in recent years. In this method, the same functions used in the CAD system are used to describe geometry and approximate the field variables in numerical discretization. The isogeometric finite element method (IGFEM) has widely been used to study various problems for a long time, but in the field of the boundary element method (BEM), researches about the isogeometric analysis have not yet attained more attentions. In this paper, we use the isogeometric boundary element method (IGBEM) to carry out the calculation of effective elastic properties and stress states of doubly periodic inclusions with complex shapes. The results obtained by the IGBEM are compared with those from the finite element method (FEM). We believe that this work clearly presents the power of the IGBEM and provides an efficient approach to investigate elastic behavior of composites containing various microstructures.

First-principles calculations of structural, electronic, elastic and thermal properties of phase M2SiC (M=Ti, V, Cr, Zr, Nb, Mo, Hf, Ta and W)

The structural, electronic and elastic properties of the M2SiC phases were studied, where M are 3d, 4d, and 5d early transition metals. The valence electron concentration (VEC) effect of Ti, V, Cr, Zr, Nb, Mo, Hf, Ta and W on these properties was examined. The C44 saturates for a VEC value in surrounding of 8.5 for each serie. Hf-s, Ta-s and W-s electrons mainly contribute to the density of states at the Fermi level, and should be involved in the conduction properties. The distortion increases with increasing VEC and decreasing kc/ka factor except for the series M=Ti, V and Cr, where it is lower at the VEC value of 8.5 (it follows a parabolic variation). The M2SiC was characterized by a profound anisotropy for the shear planes (1010) and compressibility in the direction is higher than that along the cone except for W2SiC, where it is lower.

DFT calculations of structural, electronic, optical and elastic properties of scintillator materials BaCl2 and BaBr2

Detailed structural, electronic, optical and elastic properties with their pressure dependence of two barium halide scintillators are presented using first-principles calculations based on the density functional theory formalism. Only PBE-GGA results tally the closest with experimental results of a band gap of 4.26 eV for BaBr2 and 4.96 eV for BaCl2. The electron () and hole () effective masses are determined to be 0.88 and 0.95 for BaCl2 and 0.86 and 0.91 for BaBr2. The pressure dependence yields the pressure coefficient of the band gap as −4.34 × 10−2 eV GPa−1 and −3.77 × 10−2 eV GPa−1 for BaBr2 and BaCl2, respectively. All the elastic constants and the related parameters are calculated for both the halides. The optical and elastic properties clearly indicate the anisotropy along the three crystallographic directions of these two scintillators. The scintillation properties of the two compounds with and without doping are discussed in the light of these properties.

First-principles calculations of structural stability and elastic properties of REB12 strengthening phases in boriding Mg–RE alloys

The effect of rare-earth elements (REs) on formation and elastic properties of strengthening precipitates in boriding Mg–RE alloys was determined by first-principles calculations. The preferential formation of a B12-cluster during boriding process results in the appearance of the only REB12 strengthening phases. The REB12 compounds possess the high hardness, which is mainly associated with the strong covalent bondings of B12-cluster. The RE types hardly affect the hardness of REB12 compounds, which is partially elucidated owing to a low fraction of RE–B metallic bondings.

Computational Study of ScN

Abstract We report calculations of pressure-induced structural phase transition and elastic properties of the NaCl-type scandium nitride at room temperature. For the present study a Realistic Interaction Potential Approach (RIPA) model (including the covalency and temperature effect) has been developed. The pressure-induced transition is found to be first order. It is examined that the present compound is more stable in NaCl-phase. It is predicted that at high pressures present compound undergoes a structural phase transition from the NaCl structure into the denser CsCl atomic configuration. The phase transition pressures and associated volume collapses obtained from present potential model show a generally good agreement with available experimental data and others.

Macroscopic elastic properties of textured ZrN-AlN polycrystalline aggregates: Fromab initiocalculations to grain-scale interactions

Despite the fast development of computational materials modelling, theoretical description of macroscopic elastic properties of textured polycrystalline aggregates starting from basic principles remains a challenging task. In this communication we use a supercell-based approach to obtain the elastic properties of random solid solution cubic ZrAlN system as a function of the metallic sublattice composition and texture descriptors. The employed special quasi-random structures are optimised not only with respect to short range order parameters, but also to make the three cubic directions $[1\,0\,0]$, $[0\,1\,0]$, and $[0\,0\,1]$ as similar as possible. In this way, only a small spread of elastic constants tensor components is achieved and an optimum trade-off between modelling of chemical disorder and computational limits regarding the supercell size is achieved. The single crystal elastic constants are shown to vary smoothly with composition, yielding $x\approx0.4$-0.5 an alloy constitution with an almost isotropic response. Consequently, polycrystals with this composition are suggested to have Young's modulus independent on the actual microstructure. This is indeed confirmed by explicit calculations of polycrystal elastic properties, both within the isotropic aggregate limit, as well as with fibre textures with various orientations and sharpness. It turns out, that for low AlN mole fractions, the spread of the possible Young's moduli data caused by the texture variation can be larger than 100 GPa. Consequently, our discussion of Young's modulus data of cubic ZrAlN contains also the evaluation of the texture typical for thin films.

Theoretical calculations of structural, electronic, optical, elastic, and thermal properties of YX3 (X = In, Sn, Tl, and Pb) compounds based on density functional theory

The structural, electronic, optical, elastic, mechanical, and thermal properties of the isostructural and isoelectronic nonmagnetic YX3 (X = In, Sn, Tl, and Pb) compounds, which crystallize in AuCu3-type structure have been studied using the full potential linearized augmented plane wave (FP-LAPW) method. The calculations are carried out within the PBE-GGA, WC-GGA, and PBE-sol GGA for the exchange correlation potential. The 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. All the compounds are found to be ductile in nature in accordance with Pugh’s criteria. The computed electronic band structures as well as density of states show that these compounds are metallic with sturdy hybridization near the Fermi level. The bonding features of these compounds are analyzed using the electronic charge density plots in the (100) crystallographic plane and their analysis revealed that the chemical bond between Y and X is mainly ionic along with weak covalent bonding. The Fermi surfaces for these compounds at ambient pressure are also studied. The linear optical properties of these compounds are also studied at the ambient conditions. The variations of elastic constants, elastic moduli, and Debye temperatures of these compounds as a function of pressure are also reported.

Structural, elastic, thermal and electronic properties of M2X (M = Sr, Ba and X = Si, Ge, Sn) compounds in anti-fluorite structure: first principle calculations

First principle calculations of structural, elastic, thermal and electronic properties of M2X (M = Sr, Ba and X = Si, Ge, Sn) compounds in the anti-fluorite type structure are performed within the framework of density functional theory. The lattice constant, bulk modulus, derivative of bulk modulus and ground state energy are calculated. The calculated elastic properties reveal that Sr2Si, Sr2Ge, Ba2Si and Ba2Ge are classified as brittle, while Sr2Sn and Ba2Sn show ductile nature. It is noted that these compounds are elastically stable and the Debye temperature value decreases from Sr to Ba and from top to bottom in group IV-A of periodic table. From electronic charge density plot in the (110) crystallographic plane it is observed that in Sr2X, Sr shows ionic bond nature with X, while in Ba2X, Ba forms partially ionic and partially covalent bond with X. The density of states and the electronic band structures are also presented. We have found that these compounds possess narrow and direct band gaps. The values of the energy gaps obtained by using the modified Becke–Johnson approach are better than the values obtained from the generalized gradient approximation.

First-principle study of structural, elastic and electronic properties of Th monopnictides

In this work, first principles calculation of structural, electronic and elastic properties of thorium monopnictides ThX (N, P, As, Sb and Bi) are presented. The calculations are performed by a developed full-potential augmented plane wave plus local orbitals (FP-L/APW+lo) method within the density functional theory (DFT). The exchange and correlation potential energies are treated according to the generalized gradient approximation (GGA) using the Perdew, Burke, Ernzerhof (PBE) parameterization, and the local density approximation (LDA). We have calculated the lattice parameters, bulk modulii and the first pressure derivatives of the bulk modulii. The elastic properties of the studied compounds are only investigated in the most stable calculated phase. We have obtained Young’s modulus, shear modulus, Poisson’s ratio, anisotropy factor and Kleinman parameter by the aid of the calculated elastic constants. We discuss the total and partial densities of states and charge densities.

First-principles calculations of elastic and thermodynamic properties of the four main intermetallic phases in Al–Zn–Mg–Cu alloys

First-principles calculations are performed to investigate the structural, elastic, and thermodynamic properties of the four main intermetallic phases, namely, MgZn2, Al2CuMg, Al2Cu, and Al3Zr, in Al–Zn–Mg–Cu alloys. The calculated lattice parameters agree with experimental and theoretical values. The formation enthalpy (ΔH) decreases in the order Al3Zr>MgZn2>Al2CuMg>Al2Cu, whereas the binding energy (Eb) decreases in the order Al3Zr>Al2Cu>Al2CuMg>MgZn2. The calculated result is in accordance with the experimental phenomena. The elastic constants Cij, aggregate elastic modulus (B, G, E), Poisson’s ratio, elastic anisotropy, and Debye temperature have been calculated. The calculated intermetallic phases exhibit elastic anisotropy on the basis of the universal elastic anisotropy index AU. According to the critical values for B/G and Poisson’s ratio, MgZn2 is a ductile phase, whereas Al2CuMg, Al2Cu, and Al3Zr are brittle phases. The Debye temperature decreases in the order Al3Zr>Al2CuMg>Al2Cu>MgZn2. The electronic structures have been investigated based on band structures and density of states. Metallic bonding mode coexists with a fractional ionic interaction in MgZn2, Al2CuMg, and Al2Cu. In Al3Zr, metallic bond coexists with covalent interaction. The temperature and pressure dependencies of volume, heat capacity, and thermal expansion coefficient are investigated systematically in pressures ranging from 0GPa to 20GPa and at temperatures ranging from 0K to 900K.

Ab initio calculations of structural, elastic, and thermodynamic properties of HoX (X=N, O, S and Se)

We investigated the structural, elastic, and thermodynamic properties of HoX (X= N, O, S and Se), a series of pnictides and chalcogenides based on the rare-earth metal, Ho. These properties were studied by first-principles calculations of the total energy using the full-potential linearized augmented plane wave method. Calculations were performed within the generalized gradient approximation for the exchange correlation potential. Structural parameters, namely, lattice parameter, bulk modulus and its pressure derivate, and cohesive energy with and without spin polarization of the structures NaCl, CsCl, ZB, tetragonal crystal, WC, NiAs, PbO, and wurtzite were determined. Elastic constants were derived from the stress–strain relation at 0K. We also determined the thermodynamics properties for HoX through the quasiharmonic Debye model. The temperature and pressure variation of the volume, bulk modulus, thermal expansion coefficient, heat capacities, and Debye temperature at various pressures (0–50GPa) and temperatures (0–1500K) were predicted.

First principles calculation of elastic and magnetic properties of Cr-based full-Heusler alloys

We present an ab-initio study of the elastic and magnetic properties of Cr-based full-Heusler alloys within the first-principles density functional theory. The lattice constant, magnetic moment, bulk modulus and density of states are calculated using the full-potential nonorthogonal local-orbital minimum basis (FPLO) code in the Generalized Gradient Approximation (GGA) scheme. Only the two alloys Co2CrSi and Fe2CrSi are half-metallic with energy gaps of 0.88 and 0.55eV in the spin-down channel respectively. We have predicted the metallicity state for Fe2CrSb, Ni2CrIn, Cu2CrIn, and Cu2CrSi alloys. Fe2CrSb shows a strong pressure dependent, e.g. exhibits metallicity at zero pressure and turns into a half-metal at P≥10GPa. The total and partial magnetic moments of these alloys were studied under higher pressure, e.g. in Co2CrIn, the total magnetic moment is almost unchanged under higher pressure up to 500GPa.

First-principles calculations of structural phase transition and elastic properties of BeTe under high pressure

The structural phase transition and elastic properties of BeTe are investigated by first-principles calculations using pseudopotential plane-wave method within the generalized gradient approximation. The calculated structural parameters of BeTe are consistent with previous experimental and theoretical results. According to the enthalpy and pressure data, it is predicted that the pressure value in the phase transformation from B3 to B8 is 35.88 GPa, which is well in line with the experimental data of 35 ± 5 GPa. Especially the elastic constants of B8 under high pressure of BeTe are studied for the first time, from which the elastic moduli, compressional and shear wave velocities as well as Debye temperature as a function of pressure are analysed successfully.

Density functional theory and evolution algorithm calculations of elastic properties of AlON

Different models for aluminum oxynitride (AlON) were calculated using density functional theory and optimized using an evolutionary algorithm. Evolutionary algorithm and density functional theory (DFT) calculations starting from several models of AlON with different Al or O vacancy locations and different positions for the N atoms relative to the vacancy were carried out. The results show that the constant anion model [McCauley et al., J. Eur. Ceram. Soc. 29(2), 223 (2009)] with a random distribution of N atoms not adjacent to the Al vacancy has the lowest energy configuration. The lowest energy structure is in a reasonable agreement with experimental X-ray diffraction spectra. The optimized structure of a 55 atom unit cell was used to construct 220 and 440 atom models for simulation cells using DFT with a Gaussian basis set. Cubic elastic constant predictions were found to approach the experimentally determined AlON single crystal elastic constants as the model size increased from 55 to 440 atoms. The pressure dependence of the elastic constants found from simulated stress-strain relations were in overall agreement with experimental measurements of polycrystalline and single crystal AlON. Calculated IR intensity and Raman spectra are compared with available experimental data.

First-principles calculations of structural, elastic and electronic properties of Li2B12H12

We investigate the structural, elastic and electronic properties of Li2B12H12 using the first-principles method. Our calculations show that the lowest energy structure of Li2B12H12 is monoclinic C2/m type. We take the monoclinic C2/m Li2B12H12 as a representative to carry out the corresponding theoretical studies. The independent elastic constants are successfully obtained from the strain energy–strain curve calculations. The Shear and Young‘s moduli, as well as Poisson‘s ratio for ideal polycrystalline Li2B12H12 are calculated. The shear anisotropic factors and elastic anisotropy of Li2B12H12 are analyzed. The Debye temperature and the average elastic wave velocity are derived from theoretical elastic constants. According to the obtained results, the monoclinic C2/m Li2B12H12 is found to be mechanically stable and brittle at zero temperature and zero pressure. Furthermore, the density of states and electron charge density distributions are studied. The insulator Li2B12H12 is a technologically interesting indirect hydrogen storage material for further studies.

Ab initio calculations of elastic properties of Fe–Cr–W alloys

Reduced activation ferritic/martensitic (RAFM) steels are considered as the primary candidate for the blanket module in International Thermonuclear Experimental Reactor (ITER), and the basic composition of RAFM steels is Fe–Cr–W alloy. Using the exact muffin-tin orbitals method (EMTO) combined with coherent potential approximation (CPA), we investigated composition dependence of elastic properties for Fe–Cr–W random alloys in the composition range of 7.8–10.0wt.% of Cr and 1.0–2.0wt.% of W. Bulk modulus, shear modulus, Young’s modulus, B/G ratio, and Poisson ratio are discussed as functions of ternary composition. The elastic moduli of Fe–Cr–W alloys increase with chromium content in the studied range of alloy compositions, the effect of tungsten is slight.

Three-dimensional microstructure and numerical calculation of elastic properties of alpine snow with a focus on weak layers

AbstractThe microstructure and stratigraphy of a snowpack determine its physical behaviour. Weak layers or weak interfaces buried under a slab are prerequisites for the formation of dry-snow slab avalanches, and a precise characterization of weak layers or interfaces is essential to assess stability. Yet their exact geometry and micromechanical properties are poorly known. We cast weak layers and their adjacent layers in the field during two winters and reconstructed their three-dimensional microstructure using X-ray microcomputer tomography. The high resolution of 10–20 μm allowed us to study snow stratigraphy at the microstructural scale. We quantified the microstructural variability for 32 centimetre-sized layered samples and we calculated Young’s modulus and Poisson’s ratio by tomography-based finite-element simulations. Layers in a sample could therefore be differentiated not only by a change in morphology or microstructure, but also by a change in mechanical properties. We found a logarithmic correlation of Young’s modulus with density for two different density ranges, consistent with previous studies. By calculating the relative microstructural changes within our samples, we showed that a large change could indicate a potential weak layer, but only when the weak layer and both adjacent layers, i.e. the sandwich, were considered.

Role of oxygen impurity on the mechanical stability and atomic cohesion of Ta₃N₅ semiconductor photocatalyst.

Oxygen is a natural impurity in the Ta3N5 semiconductor photocatalyst and very difficult to be completely eliminated in different growth conditions. In this study, density functional theory calculations are performed to unravel the cause of natural existence of oxygen impurity in Ta3N5 from the perspectives of mechanical stability and atomic cohesion. The elastic properties calculations show that the oxygen impurity in Ta3N5 is able to remedy the weakened mechanical stability induced by the nitrogen vacancy in Ta3N5. The atomic cohesion calculations show that the oxygen impurity in Ta3N5 enlarges the valence band width of Ta3N5, suggesting that the oxygen impurity is able to strengthen the atomic cohesion of Ta3N5. Based on our calculation results, we propose that the charge-compensation codoping is a promising strategy to improve the water splitting ability of Ta3N5 and simultaneously maintain the mechanical stability and enhanced atomic cohesion of Ta3N5.