Polycrystalline Elastic Moduli Research Articles

Cohesive, elastic and anisotropic properties of s-, p- and d-block fission metals substituted Fe–Zr intermetallics

Density functional theory (DFT) based calculations are performed to study cohesive, elastic and anisotropic properties of c-Fe2Zr, t-FeZr2 and o-FeZr3 phases in the presence of s-, p- and d-block fission metals (FMs), viz. Rb, Sr, Cs, Ba, In, Sn, Sb, Te, Y, Nb, Mo, Tc, Ru, Rh, Pd, Ag and Cd. The FM substituted intermetallics are found to be thermodynamically stable owing to their negative formation energy. The Gibbs free energy of mixing is calculated to find the solubility of these FMs in these intermetallics. The calculated single crystal elastic constants suggest that all the FM substituted phases are mechanically stable. We also report the change in polycrystalline elastic moduli, viz. bulk, shear and Young moduli of the pristine intermetallics on incorporation of these FMs. The substitution of FMs in the FeZr2 phase increases its intrinsic ductility; while that in FeZr3 phase decreases it. The degree of anisotropy exhibited by the intermetallics follow the order FeZr2> FeZr3> Fe2Zr. The substitution of FMs does not affect the anisotropic behavior of Fe2Zr and FeZr2 phases, but slightly changes that of FeZr3 phase. Finally, the potential of these intermetallics to incorporate the FMs is discussed.

Study of structural, elastic, electronic, optical and magnetic properties of Heusler Mn2NiAl: Ab initio calculations

In this paper, we will investigate the structural, electronic, mechanical, magnetic and optical properties of Heusler Mn2NiAl (MNA) compound using the Perdew–Burke–Ernzerhof generalized gradient approximation (PBE-GGA) of the full potential linearized augmented plane-wave method for exchange and use correlations, modified Becke–Johnson and GGA+U Hubbard parameter. The calculated band structure (BS) and density of states (DOS) of MNA showed a metallic (GGA), nearly half-metallic (mBJ) and half metallic (GGA+U) behavior. Moreover, the magnetic computed magnetic moments by GGA+U are higher compared to GGA and mBJ results. Bulk modulus, shear modulus, Voigt and Reuss polycrystalline elastic modulus, Debye temperature, sound velocities, the melting temperatures, [Formula: see text] ratio, Young’s modulus and Poisson’s ratio were obtained. The elastic anisotropy of MNA alloy was analyzed using 2D and 3D figures of directional dependence of Poisson’s ratio, shear modulus, linear compressibility and Young’s modulus. Studies have shown that the Heusler material MNA has magnetic and anisotropic properties and is mechanically stable.

Physical properties of Be-based fluoroperovskite compounds XBeF3 (X = K, Rb): a first-principles study

In this study, we used the ab-initio computational tools as implemented in the CASTEP code to explore the effects of pressure on the structural, elastic, electronic, thermodynamic and optical properties of the fluoroperovskite compounds XBeF3 (X = K, Rb) based on Being. Exchange–correlation interactions were modeled using the GGA-PBEsol functional. The ground state of the title materials was characterized by calculating the optimized lattice parameter, the bulk modulus B and its pressure derivative, and the Goldsmith tolerance factor. These materials exhibit structural stability in the cubic structure even when subjected to significant pressure levels, extending up to 18 GPa. The analysis of numerical assessments of single-crystal elastic constants (Cij ), polycrystalline elastic moduli, namely shear modulus (G), Young’s modulus and Poisson’s ratio, as well as the anisotropy factor (A), highlights the mechanical stability, elastic anisotropy and ductility of considered the compounds. The thermodynamic properties of these materials were studied through the Debye quasi-harmonic model. Analysis of energy band structures and density of states spectra shows that XBeF3 (X = K, Rb) is insulating in nature, with band gaps of 7.99 and 7.26 eV, respectively. Additionally, we calculated the linear optical spectra, including dielectric function, absorption coefficient, refractive index, optical reflectivity, and energy loss function. Based on the results obtained, these materials could be used in various optoelectronic devices operating in the UV spectrum and in energy storage devices.

Hydrogen storage: Investigation of the elastic properties of Mg7NbH16 hydride

Structural, mechanical and electronic structure properties of Mg7NbH16 were investigated using the norm-conserving pseudo-potentials and plane waves (PP-PW) within the general gradient approximation (GGA) in the frame of density functional theory (DFT). The computed equilibrium lattice constants are in excellent agreement with the available experimental and theoretical data. The elastic constants Cij of Mg7NbH16 were calculated for the first time. The Mg7NbH16 compound is found to be mechanically stable. The bulk modulus of single crystals has been derived using elastic constants. The results are discussed and compared with the calculated bulk modulus reported in the literature. The polycrystalline elastic moduli (namely: the shear modulus, Young's modulus, Poisson's ratio, Lamé's coefficients, sound velocities and the Debye temperature) were derived from the obtained single-crystal elastic constants. According to the obtained results, Mg7NbH16 can be classified as ductile material. The shear anisotropic factors and the elastic anisotropy are also discussed. A Debye temperature of 619 K was also determined using theoretical elastic constants.

The physical properties of Sc2PbC: A first-principles calculations

The structural, electronic, elastic, hardness, fracture toughness, and thermodynamic properties of the newly synthesized MAX phase Sc2PbC were studied for the first time through the first-principles calculations. The optimized lattice parameters are in agreement with the experimental data. The thermodynamic and mechanical stability of Sc2PbC is verified based on the formation enthalpy and single-crystal elastic constants. By analyzing the polycrystalline elastic moduli, it is found that Sc2PbC is brittle, very soft, easily machinable, and exhibits elastic anisotropy. Finally, thermodynamic properties such as Debye temperatures, thermal conductivity, melting temperature, and the temperature dependence of heat capacity are investigated.

First-principles study of the phase stability and elastic properties of TiVNbMoM (M = Al, Sc, Ni and Cu) high entropy alloys

The ab initio exact muffin-tin orbitals (EMTO) method in combination with the coherent potential approximation (CPA) were used to study the influence of alloying elements M = Al, Sc, Ni and Cu on the phase stability, lattice constants, elastic constants, polycrystalline elastic moduli and electronic structure of equiatomic and non-equiatomic TiVNbMoM refractory high entropy alloys. The agreement between our results and the available experimental and theoretical data is quite good. It was found that the equiatomic systems are stable in the body-centered cubic (bcc) structure. Alloying elements decrease the stability of the bcc against the face-centered cubic (fcc) and the hexagonal close-packed (hcp) structures. Scandium enlarges the lattice constants of equiatomic and non-equiatomic systems significantly. According to the calculated bulk modulus to shear modulus, Poisson’s ratio and Vickers hardness, all studied equiatomic and non-equiaomic systems are found to be ductile. However, alloying elements Al, Ni and Cu reduce the ductility and improve the hardness of equiatomic and non-equiatomic TiVNbMoM systems, while the ductility (hardness) of non-equiatomic systems enhances (reduces) by substitution with Sc element. The present theoretical results provide insight for the design and improvement of high entropy alloys and complete information on the alloying effects.

A systematic description of the thermodynamic, elastic and mechanical properties of binary Zr-based bcc alloys from first principles

The effects of the dissolution of 3d, 4d, and 5d metals, as well as Al, In, and Sn in the bcc lattice of Zr, were studied within the framework of the electron density functional theory. Using the EMTO-CPA method, we calculated the lattice parameters, enthalpies of mixing, single-crystal elastic constants C11, C12, C44, and C', polycrystalline elastic moduli E, G, and plasticity characteristics of disordered Zr-based bcc alloys over a wide concentration range. The PAW-SQS method was used to study the effects of alloying on the specified properties of bcc Zr-X alloys, where X is a series of 4d elements Nb, Mo, Tc, Ru, Rh and 5d elements Ta, W, Re, Os, Ir for concentration cuts 6.25, 25 and 50 at.%. The analysis of concentration and periodic dependences of properties of alloys, their stability is carried out.

Elastic anisotropy and thermal properties of Zr-Al-N ternary nitrides using first-principles explorations

First-principles calculations based on density functional theory (DFT) were employed to explore the anisotropies in elastic and thermal properties of six Zr-Al-N ternary nitrides (Zr2AlN, Zr5Al3N, ZrAlN2, Zr3AlN4, ZrAl3N4 and Zr3AlN). The single-crystal elastic constants and poly-crystalline elastic moduli were acquired by using Voigt-Reuss-Hill approximations. The elastic anisotropies of the above six Zr-Al-N ternary nitrides were characterized by a three-dimensional (3D) surface constructions and two-dimensional (2D) plane projections. The elastic modulus anisotropy is in the order of ZrAlN2 > Zr3AlN > ZrAl3N4 > Zr3AlN4 >Zr2AlN > Zr5Al3N. Furthermore, these six Zr-Al-N ternary nitrides have the hardness ranging from 12.7 to 18.7 GPa. Moreover, these six ternary nitrides all meet the brittleness criteria in terms of Poisson's ratio, GH/BH and Cauchy pressure. Finally, the sound velocities, Debye temperature, thermal conductivity and their anisotropies of these Zr-Al-N ternary nitrides are discussed, showing that the sound velocities and Debye temperature are anisotropic in the [001] and [100] directions.

Physical properties of BaRu2X2 (X = P, As) superconducting compound sunder pressure effects: Ab initio study

We report the results of a detailed ab initio investigation of the pressure effects up to 18 GPa on the structural, elastic and thermodynamic properties of the superconducting compounds BaRu2P2 and BaRu2As2. The exchange-correlation effects were modeled through the PBEsol version of the generalized gradient approximation. The calculated equilibrium lattice parameters are in good agreement with the available experimental counterparts. The lattice parameter c decreases with increasing pressure faster than the lattice parameter a. The computed single-crystal elastic constants (Cij) show that both BaRu2P2 and BaRu2As2 are mechanically stable under pressure effect up to 18 GPa. Pressure dependence of the single-crystal and polycrystalline elastic moduli, and related physical parameters, namely Cij, Young's modulus, shear modulus, bulk modulus, Poisson's ratio, average sound velocity, Debye temperature (θD), minimum thermal conductivity (Kmin), melting temperature (Tm) and Vickers hardness (HV), were successfully calculated for the pressure range 0-18 GPa. The quasi-harmonic Debye model was successfully used to explore the temperature and pressure dependencies of the unit cell volume, bulk modulus, isochoric and isobar heat capacities, volume thermal expansion coefficient and Debye temperature. The good agreement between the results obtained using the quasi-harmonic Debye model and those corresponding deduced from the elastic constants constitutes proof of the reliability of the results obtained.

Theoretical simulation structural, elastic, electronic, optical, vibrational and thermal properties of AgGaxIn1-xS2 (x = 0, 0.25, 0.5, 0.75, 1)

The elasticity, vibration and thermodynamic properties of single crystal materials are very important in the field of laser and nonlinear optics. Therefore, it is very important to understand the physical mechanism of thermal properties in such systems. In this work, the structural, elastic, vibrational and thermodynamic properties of the AgGaxIn1-xS2 (x = 0, 0.25, 0.5, 0.75, 1) have been performed systematic within generalized gradient approximation (GGA) of Perdew-Burke-Ernzerhof (PBE). The results show that the AgGaxIn1-xS2 series have similar physical properties. When Ga concentration increases gradually, the lattice constants (a and c) decrease drastically with the increase of Ga content x. The polycrystalline elastic moduli including bulk modulus B, Young's modulus E, shear modulus G and Poisson's ratio v have also been successfully calculated. The brittle and ductile properties were judged by using B/G and Poisson's ratio. The anisotropy was characterized by calculating several different anisotropic indexes and the 3D figures of directional dependences of reciprocals of bulk modulus. Use the hybrid functional HSE06 to study the electronic properties of AgGaxIn1-xS2, and suggest that the HSE06 hybrid functional can obtain a more reasonable band. In addition, the optical spectrum are derived and main spectral features are interpreted in terms of the electronic structure. The calculated results of vibrational characters indicate that AgGaxIn1-xS2 (x = 0, 0.25, 0.5, 0.75, 1) are dynamic stability as increasing of Ga concentration from 0.0 to 1. Finally, the thermodynamic properties related to phonons have been realized and explored.

Theoretical Study on the Structural, Elastic, Electronic and Thermodynamic Properties of Long-Period Superstructures h- and r-Al2Ti under High Pressure.

The formations of long-period superstructures strongly influence the properties of Al-rich L1-TiAl intermetallic alloys. To soundly understand the role of the superstructures in the alloys, fundamentals about them have to be known. In the present work, the structural, elastic, electronic and thermodynamic properties of h- and r-AlTi long-period superstructures under pressure up to 30 GPa were systematically investigated using first-principles calculations based on density functional theory. The pressure dependence of structural parameters, single-crystal elastic constants, polycrystalline elastic modulus, Cauchy pressures and elastic anisotropy were successfully calculated and discussed. The total and partial densities of states at different pressures were also successfully calculated and discussed. Furthermore, combining with quasi-harmonic approximation, the effects of the pressure on the temperature dependent volume, isothermal bulk modulus, thermal expansion coefficient, heat capacity and Gibbs free energy difference were successfully obtained and discussed. Our results were consistent with the available experimental and theoretical values.

Ab initio study of the pressure dependence of mechanical and thermodynamic properties of GeB2O4 (B = Mg, Zn and Cd) spinel crystals

Ab initio full-potential (linearized) augmented plane-wave plus local orbitals (FP-(L)APW + lo) calculations are performed to study the hydrostatic pressure dependence of the mechanical and thermodynamics properties of GeMg2O4, GeZn2O4, and GeCd2O4 cubic spinels. The calculated equilibrium structural parameters using both the local density approximation and the generalized gradient approximation are well consistent with the available theoretical and experimental data in the literature. The monocrystalline elastic constants are predictet using the energy-strain scheme. The polycrystalline elastic moduli are determined from the monocrystalline elastic constants through the Voigt-Reuss-Hill approximations. To understand the mechanical behavior of the investigated compounds, assessments of their mechanical stability, ductility/brittleness, sound velocities, elastic anisotropy, pressure-dependent elastic constants, and Debye temperature are made. Regarding thermodynamic properties, temperature dependence of the lattice parameter, bulk modulus, isochoric and isobaric heat capacities, volume thermal expansion coefficient, and Debye temperature at different fixed pressures are explored through the quasi-harmonic Debye model coupled with the FP-(L)APW + lo approach.

Elastic, electronic, optical and thermoelectric properties of the novel Zintl-phase Ba2ZnP2

We report and discuss the results of a detailed first-principles calculations of the structural, elastic, electronic, optical and thermoelectric properties of the new Zintl phase dibarium zinc diphosphide Ba2ZnP2. The calculated structural parameters using the GGA-PBEsol functional are in excellent agreement with the available experimental counterparts. From the monocrystalline elastic constants numerically estimated through the stress-strain technique, a set of related properties, viz., mechanical stability, elastic anisotropy, brittle/ductile character, anisotropic sound velocities, polycrystalline elastic moduli, including isotropic bulk modulus, shear modulus, Young's modulus, Poisson's ratio, average sound velocity and Debye temperature, are deduced. The electronic and optical properties are investigated through the state-of-the art FP-(L)APW + lo method with the accurate TB-mBJ potential. Ba2ZnP2 is an indirect semiconductor with a gap of 1.24 eV. The charge-carrier effective masses are calculated. The valence band maximum is less dispersive than the conduction band minimum. The microscopic origins of the electronic states composing the energy bands are determined via the PDOS diagrams. Topological analysis of the charge density shows that a covalent character is dominantly ruling the Zn–P bond inside the block ZnP4, while an ionic bonding is mainly ruling the bond between the cation Ba and the polyanion ZnP4. Frequency-dependent macroscopic linear optical functions are predicted in a wide energy range 0–30 eV. Within the visible spectra, the calculated magnitude of the absorption coefficient, reflectivity and refractive index are in the ranges ∼4−35×104cm−1, 29−36% and 3.18−3.47, respectively. The semi-classical Boltzmann transport theory within the constant relaxation time approximation is used to study the thermoelectric properties. The title compound has a figure of merit of ∼1.77 at 300 K, which makes it a potential candidate for thermoelectric applications.

Ab initio systematic description of thermodynamic and mechanical properties of binary bcc Ti-based alloys

The effects of the dissolution of 3d, 4d and 5d metals and Al, Ga, Ge, In and Sn in the bcc Ti lattice (β-phase) were studied within the framework of first-principles calculations. Lattice parameters, mixing enthalpies, single-crystal elastic constants C11, C12, C44 and C′, polycrystalline elastic moduli E, G, and plasticity characteristics of bcc Ti-based solid solutions in a wide concentration range up to 50 at% were investigated using the EMTO-CPA method. The PAW-SQS method was used to study the effects of alloying and local atomic relaxations on the indicated properties of Ti-X bcc alloys, where X is a series of 4d elements Nb, Mo, Tc, Ru, Rh, and 5d elements Ta, W, Re, Os, Ir for the set of concentrations: 6.25, 25 and 50 at%. The effect of concentration and periodic dependences on the properties of alloys and the dependence of elastic properties on the electronic structure were analyzed. It is shown that the calculated elastic constant C′ is a convenient and useful parameter for ranking chemical elements according to the relative strength of the stabilizing effect on the β-phase, in addition, the concentration dependences of C′ demonstrate softening with concentration increasing in the case of late transition metals, thereby reflecting the tendency of these metals to form intermetallic compounds with titanium, while early transition metals show a linear grow in stability with increasing concentration.

Tetragonal distortion in magnetron sputtered bcc-W films with supersaturated carbon

Carbon has a low solid solubility in bcc tungsten at equilibrium. However, metastable supersaturated solid solutions can be synthesized with magnetron sputtering. Here, we present a systematic study on the phase stability and mechanical properties of such supersaturated W–C solid solutions. Θ–2θ scans show a split of the 200/020 and the 002 peaks for supersaturated films which is explained by a tetragonal distortion of the bcc structure. This split increases with increasing C content and is maximized at 4 at.% C, where we observe an a/b axis of 3.15–3.16 Å and a c-axis of 3.21–3.22 Å. We performed first-principles calculations of lattice parameters, mixing enthalpies, elastic constants and polycrystalline elastic moduli for cubic and tetragonal W–C solid solutions. Calculations show that tetragonal structure is more stable than the bcc supersaturated solid solution and the calculated lattice parameters and Young’s moduli follow the same trends as the experimental ones as a function of C concentration. The results suggest that supersaturated films with lattice distortion can be used as a design approach to improve the properties of transition metal films with a bcc structure.

Elastic anisotropies, thermal conductivities and tensile properties of MAX phases Zr2AlC and Zr2AlN: A first-principles calculation

In this study, the mechanical stability, elastic properties, including single-crystal elastic constants, polycrystalline elastic modulus and elastic anisotropy, Debye temperatures, electronic properties, minimum thermal conductivities and tensile character of Zr2AlC and Zr2AlN were calculated by first-principles calculations based on density functional theory. The results showed that Zr2AlX (X = C, N) are mechanically stable and anisotropic in elastic properties, and the degree of elastic anisotropy of Zr2AlN is slightly greater than Zr2AlC, and the sound velocities and minimum thermal conductivities of Zr2AlC and Zr2AlN along the [001] and [100] directions are also anisotropic. Moreover, the density of states (DOS) and charge density difference distributions showed that these Zr2AlX have metallic-covalent-ionic mixed bonds. Finally, the calculated tensile properties along the [001] and [110] directions of these MAX phases showed that the tensile strength along the [110] direction is greater than that along the [001] direction.

A comprehensive study of the structural, elastic, electronic, and optical properties of the tetragonal sodium chalcogenides NaAlX 2 (X = O, S, Se, Te)

ABSTRACT We used first-principles electronic structure calculations to investigate the structural, elastic, electronic and optical properties of the already synthesised NaAlSe2 and NaAlTe2 tetragonal compounds and the predicted NaAlO2 and NaAlS2 tetragonal systems. The computed structural parameters using the GGA-PBE approach are consistent with the corresponding experimentally determined ones. The calculated single-crystal and polycrystalline elastic moduli show that the studied materials are mechanically stable and of a weak stiffness with strong elastic anisotropy. Calculated band structures reveal that NaAlO2, NaAlS2 and NaAlSe2 are semiconductors with an indirect bandgap of Z-Γ type, while NaAlTe2 is of a direct bandgap of Z-Z type. The calculated frequency-dependent linear optical functions show that the title compounds are characterised by significant optical anisotropy and high optical absorption for a wide photon energy range in the UV spectrum.

Influence of high pressure on structural, electronic and mechanical properties of tetragonal FeH5

First-principles method is performed to investigate the structural, electronic, and mechanical characteristics of the tetragonal I/4mmm-FeH5 in the pressure range from 100GPa to 300 GPa. At 130 GPa and 150 GPa, the lattice parameters of I/4mmm-FeH5 are matched well with available values. The pressure has a more significant influence on the c→ direction than the a→and b→ direction. Electronic calculations predicted that the I4/mmm-FeH5 has weak metallic behaviors and the ionic bond between Fe and H atom under pressure. The obtained elastic constants reveal the I/4mmm-FeH5 is mechanically stable between 100 GPa and 300 GPa. The bulk, shear, and Young's modulus are evaluated by Voigt-Reuss-Hill approximation. All these polycrystalline elastic moduli exhibit a monotonic feature as a function of pressure. The Poisson's ratio, Pugh's criterion, and Cauchy pressure indicate that the I4/mmm-FeH5 is ductile against pressure. Mechanical anisotropy is evaluated through several physical parameters. Finally, the Debye temperature estimated from the average wave velocity is found to monotonically increase with pressure.

Electronic band structure, elastic, optical and thermodynamic characteristic of cubic YF3: An ab initio study

We have calculated the bond lengths dF3→F5,7,8, dF4→F5,6,8, dF2→F5,7,8, dF1→F6,7,8, dF1→8−Y1,2,3, dF9→Y1,2,3, dF1→8−F9 and single-crystal elastic stiffness constants, Cij and polycrystalline elastic moduli at different pressures by using GGA-PBE, GGA-PBESOL and LDA approach for cubic YF3. Yttrium fluoride is found to be elastically stable in the pressure range 0–40 GPa. Shear modulus, linear compressibility and Poisson's ratio have maximum and minimum values along with different crystallographic directions, which explain their predicted anisotropy. The direct Γ-Γ band gap value 5.082 eV indicates towards the insulating character of YF3. The broad band gap is a sign that this compound should function as an emission center. We predicted the first and second-order pressure coefficients of direct and indirect band gaps using the GGA-PBE, GGA-PBESOL and LDA approaches. The estimated volumetric thermal expansion coefficient, constants volume and constant pressure heat capacities and entropy at zero pressure and 300 K are 1.66 × 105 K−1, 82.56 Jmol−1K−1 and 83.59 mol-1 K−1, respectively. The edge of the optical absorption is located at 48.5 nm which is caused by the V1−C1 transition at the Γ point in the Brillouin zone that corresponds very well to the direct band gap at Γ- Γ.

Explorations of electronic, elastic and thermal properties of tetragonal TM4N3 (TM=V, Nb and Ta) nitrides

In this work, we performed the first-principles calculations to reveal the electronic, elastic and thermal properties of the tetragonal TM4N3 (TMV, Nb, Ta) nitrides. The obtained electronic structures indicated that there is the p-d hybridization between N and TM atoms, and the electrons transfer from TM to N atoms to form TMN bonds. The polycrystalline elastic modulus was obtained from the single-crystal elastic constant. Based on the elastic constants and moduli, the elastic anisotropy was discussed by elastic anisotropy indexes and three-dimensional (3D) surface construction and its projection. Besides, Debye temperature, sound velocity and minimum thermal conductivity were also analyzed. The results showed that these nitrides are mechanically stable and ductile. Meanwhile, the elastic and thermal properties of the tetragonal TM4N3 (TMV, Nb, Ta) nitrides are anisotropic, and the order of anisotropy in elastic modulus and minimum thermal conductivity for TM4N3 (TMV, Nb and Ta) nitrides is V4N3 > Nb4N3 > Ta4N3.