Cauchy Pressure Research Articles

Investigations of Physical Properties of XTiH3 and Implications for Solid State Hydrogen Storage

Abstract This study adopts density functional theory to predict and thoroughly investigate new types of perovskite compounds for solid state storage of hydrogen. CaTiH3 and MgTiH3 perovskite hydrides are chosen and investigated using density functional theory in terms of ground state properties, electronic, mechanical, and thermodynamic properties for solid state storage of hydrogen. Stability of compounds are verified by calculating formation energies. Several crucial parameters; elastic constants, bulk, Young, Shear modulus, and Cauchy pressures are computed and analysed in great detail. Mechanical stability evaluation indicated that both compounds are mechanically stable whereas MgTiH3 is ductile whilst CaTiH3 is a brittle material. In addition, mechanical anisotropy is analysed using 2D surfaces. Both compounds showed anisotropic behaviour in all directions except for linear compressibility. Electronic band structures and their corresponding density of states of compounds are obtained. The results indicate that both compounds have metallic nature. From the results presented here, it can be predicted that MgTiH3 is a better material for hydrogen storage with a gravimetric density of ∼4.01 wt %.

Theoretical calculation into the effect of molar ratio on the structures, stability, mechanical properties and detonation performance of 1,3,5,7-tetranitro-1,3,5,7-tetrazocane/ 1,3,5-trinitro-1,3,5-triazacyco-hexane cocrystal.

Molecular dynamics (MD) simulation was conducted to research the effect of molar ratio on the thermal stability, mechanical properties, and detonation performance of HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazocane)/RDX (1,3,5-trinitro-1,3,5-triazacyco-hexane) cocrystal explosive at ambient condition. The binding energy, mechanical properties, and the detonation parameters of the pure β-HMX, RDX crystal, and the cocrystal models were got and contrasted. The results demonstrate that molar ratio has a great influence on the properties of the cocrystal system. The binding energy of the cocrystals has the maximum values at the 1:1 molar ratio, indicating that the stability of HMX/RDX(1:1) cocrystal is the best and HMX and RDX may prefer to cocrystallizing at 1:1 molar ratio. What's more, the tensile modulus (E) and shear modulus (G) of the HMX/RDX(1:1) cocrystals have the minimum value, while the C12-C44 and K/G have the maximum value, implying that the cocrystal at 1:1 molar ratio has the best mechanical properties. Simultaneously, the E, K, and G of the cocrystals are all smaller than those of β-HMX's and generally larger than those RDX's, while the Cauchy pressure (C12-C44) and K/G ratio were greater, demonstrating that cocrystallizing can improve the brittleness and enhance the ductility. The detonation velocity (D) and detonation pressure (P) decrease with the rising RDX content, while the properties are still superior to the pure RDX crystal; thus, the energy properties of the cocrystal are still excellent. In a word, HMX/RDX cocrystal at 1:1 molar ratio has the best thermal stability, mechanical properties, and the excellent energetic performance.

Molecular dynamics research on effect of doping defects on properties of PETN.

To investigate the effect of doping defects on properties of pentaerythritol tetranitrate (PETN), the "perfect" and doping defective crystal models of PETN containing pentaerythritol (PE), pentaerythritol mononitrate (PEMonoN), pentaerythritol dinitrate (PEDiN), and pentaerythritol trinitrate (PETRIN) were established, respectively. Molecular dynamics (MD) method was applied to perform simulations, and sensitivity, detonation performance, and mechanical properties were calculated and compared. The results indicate that compared with PETN (1 1 0) supercell model, the interaction energy of trigger bond and cohesive energy density of the doped defect models decreased by 2.21~12.43kJmol-1 and 0.0219~0.0421kJcm-3, respectively, indicating that the sensitivity of defective models increases and the safety decreases. The density, detonation velocity, and detonation pressure of the doped defect model decreased by 0.018~0.061gcm-3, 77.833~272.809ms-1, and 0.746~2.544GPa, respectively, and the oxygen balance is declined, indicating that the energy density of PETN decreased and the power decreased. Doped defects also cause the elastic modulus, bulk modulus, and shear modulus of PETN to decrease by 0.75~2.16GPa, 0.44~0.89GPa, and 0.30~0.89GPa, respectively. The ratio of bulk modulus to shear modulus and Cauchy pressure increased by 0.05~0.28GPa and 0.09~1.13GPa, respectively, indicating that the deformation resistance, fracture strength, and hardness of the doped defect model decrease, stiffness decreases, and flexibility and ductility increase.

Effect of Al alloying on cavitation erosion behavior of TaSi2 nanocrystalline coatings.

To broaden the scope of non-aerospace applications for titanium-based alloys, both hexagonal C40 binary TaSi2 and ternary Al alloyed TaSi2 nanocrystalline coatings were exploited to enhance the cavitation erosion resistance of Ti-6Al-4V alloy in acidic environments. To begin with, the roles of Al addition in influencing the structural stability and mechanical properties of hexagonal C40 Ta(Si1-xAlx)2 compounds were modelled using first-principles calculations. The calculated key parameters, such as Pugh's index (B/G ratio), Poisson's ratio, and Cauchy pressures, indicated that there was a threshold value for Al addition, below which the increase of Al content would render the Ta(Si1-xAlx)2 compounds more ductile, but above which no obvious change would occur. Subsequently, the TaSi2 and Ta(Si0.875Al0.125)2 coatings were prepared and their microstructure and phase composition were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Both the two coatings exhibited a uniform thickness of 15 μm and a densely packed structure mainly composed of spherically shaped nanocrystallites with an average diameter of about 5 nm. Nanoindentation measurements revealed that Al alloying reduced the hardness (H) and elastic modulus (E) values of the TaSi2 coating. Ultrasonic cavitation erosion tests were carried out by immersing coated and uncoated samples in a 0.5 M HCl solution. The cavitation-erosion analysis of the tested samples was investigated by various electrochemical techniques, mass loss weight and SEM observation. The results suggested that both coated samples provided a better protection for Ti-6Al-4V against the cavitation-erosion damage in acidic environments, but the addition of Al further improved the cavitation-erosion resistance of the TaSi2 coating.

Computational investigations of MnNiCuSb alloy for structural, elasto-mechanical and vibrational properties

The MnNiCuSb Quaternary Heusler Alloy (QHA) in Y-type I stable structure (cubic) is studied for structural, elastic, mechanical and vibrational properties by using Density Functional Theory (DFT). Three independent elastic constants [Formula: see text], [Formula: see text] and [Formula: see text] for this cubic system are computed with Generalized Gradient Approximation (GGA) functional. The mechanical parameters like Young’s modulus, Shear and Bulk modulus, Pugh’s ratio, Poisson’s ratio, anisotropic factor, Cauchy pressure are then calculated by using these cubic elastic parameters. In addition, phonon dispersion curve and phonon density of states (PDOS) are computed with norm-conserving Martins–Troullier pseudo-potential in Perturbed Density Functional Theory. The phonon dispersion curve provides reststrahlen band 0.727 THz [Formula: see text] for which material behaves as 100%. This value corresponds to Far Infra-Red (FIR) spectral region so this alloy can be used for manufacturing FIR-devices.

Structural, elastic, electronic and vibrational properties of XAl2O4 (X = Ca, Sr and Cd) semiconductors with orthorhombic structure

Structural, elastic, electronic and vibrational properties of XAl2O4 (X = Ca, Sr and Cd) compounds with orthorhombic structure are studied by first principles method within generalized gradient approximation. The calculated negative formation enthalpy for each compounds indicates the thermodynamical stability of the studied phase. Band structure calculations reveal that CaAl2O4, SrAl2O4 and CdAl2O4 compounds have a direct band gap of 4.86, 4.54 and 2.46 eV, respectively. Besides, from the analysis of the band gap values, one can notice that the replacement of Ca atoms by Sr and Cd atoms in these compounds reduces the band gap energy values. It is also observed that the CaAl2O4, SrAl2O4 and CdAl2O4 compounds are less compressible along b-axis and their compressibility decreases in the sequence SrAl2O4 > CdAl2O4 > CaAl2O4. Similarly, it is also noticeable that the CaAl2O4 compound have more resisting power against the monoclinic shear distortion along {100} plane and along {110} direction compared to CdAl2O4 and SrAl2O4 compounds. Moreover, Cauchy pressures confirm that the CaAl2O4 and SrAl2O4 compounds are ductile while the CdAl2O4 compound is brittle in nature. This fit very well with the forecast from B/G relation. The calculated elastic constants and the phonon dispersion relations of the studied compounds show that these compounds are both mechanically and dynamically stable. Moreover the temperature dependence of the specific heat and entropy have been discussed in detail and calculated Debye temperature is in good agreement with the related study in literature.

First-principles study of the mechanical and thermodynamic properties of Al4W, Al5W and Al12W under pressure

The mechanical and thermodynamic properties of Al4W, Al5W and Al12W under pressure have been studied using the first-principles calculation. The lattice constants and volume ratio decreased with increasing pressure. The calculated values of the elastic constants showed that Al4W, Al5W and Al12W were mechanically stable under pressure of 0–20 GPa. The pressure improved the resistance to deformation. According to the results of B/G ratio and the Cauchy pressure (C12–C44) calculations, Al4W and Al12W changed from brittle to ductile behavior when the pressure was above 15 GPa. The microhardness of Al4W (14.26 GPa) was larger than that of Al12W (10.39 GPa) under 0 GPa, which was in accordance with the experimental findings. The temperature and pressure had opposite effects on the heat capacity at constant volume (Cv). The ability to release or store heat for Al12W was greater than that for Al4W and Al5W.

A study on magnetic, electronic, elastic and vibrational properties of Ir2MnAl Heusler alloy for spintronic applications

The magnetic, electronic, elastic and vibrational properties of Ir2MnAl Heusler alloy are investigated with generalised gradient approximation (GGA) within the frame of Density Functional Theory (DFT). The ferromagnetic (FM) and non-magnetic (NM) states of Ir2MnAl Heusler alloy in Cu2MnAl and Hg2CuTi crystal structures have been compared. It is found that the ferromagnetic state in the Cu2MnAl structure is energetically more stable than other states. The obtained structural parameters are consistent with the current experimental and theoretical results. The spin-polarised electronic band structures of the material exhibit half-metallic behaviour with band gap in spin minority state from 0.382 eV at the Γ-X symmetry points, making it useful for spintronics applications. The calculated total magnetic moment of Ir2MnAl Heusler alloy is 4 μB which comply with the Slater-Pauling rule. Furthermore, the uniform strain has also been implemented to examine the magneto-electronic and half-metallic properties of this alloy. As a result, the half-metallicity is preserved in lattice constants between 5.872 Å and 6.187 Å. The obtained negative formation energy indicates both energetic and thermodynamic stability of this alloy. Moreover, the computed elastic constants state that this material is mechanically stable since it fulfills the Born stability criteria. The calculated B/G ratio and Cauchy pressure imply that Ir2MnAl is a ductile material in nature. Additionally, the vibrational properties are studied and it is found that this material is dynamically stable since there is no negative frequency value in phonon dispersion curves.

Tunable auxeticity and elastomechanical symmetry in a class of very low density core-shell cubic crystals

Thin-walled metamaterials based on triply periodic surfaces are relatively simple, light-weight structures that, as shown in the following, possess extraordinary material properties. As opposed to their filled counterparts, these structures can be tuned to be elastically isotropic and isotropically auxetic - the latter is the material property of extending in all directions under tensile loading in one direction. Considering level surfaces topologically equivalent to the triply periodic minimal surfaces of types Primitive, Diamond, Gyroid and I-WP, we focus on stiffness, symmetry, auxeticity, Cauchy pressure and proximity to Born mechanical instability. Our findings show that core-shell structures respond drastically differently not only in their stiffness but also for each of these observed properties compared to their counterparts with complete filling. Only core-shell topology makes elastic isotropy possible. Diamond core-shell structures are the only ones which show negative Cauchy pressure pC<0. Most notably, for the Diamond core-shell structures we observe an auxetic behavior spanning over the whole range from non-auxetic to isotropically auxetic. For the structures possessing auxeticity, negativity in the Poisson's ratio is retained for a wide deformation range spanning from small-strain tension to large-strain compression.

Theoretical prediction on the stability, electronic structure, room and elevated temperature properties of a new MAB phase Mo2AlB2

Abstarct Mo2AlB2 is a new MAB phase that has been observed in thin foils of MoAlB during TEM observation and in NaOH etched MoAlB samples. However, the structural characteristics, chemical bonding and properties of this new compound have not been investigated. In this work, geometry optimized crystal structure of Mo2AlB2 is obtained and its stability, elastic and thermal dynamic properties are investigated. Mo2AlB2 is stable in Al lean conditions, which is consistent with the exiting experimental results. It is also gauged as a damage tolerant or quasi-ductile ceramic based on the low Pugh’s shear to bulk modulus ratio (G/B = 0.544) and positive Cauchy pressure in all three crystallographic directions, which is underpinned by the metallic bonding. Mo2AlB2 also exhibits high stiffness which is attributed to the strong B–B covalent bond chains within its crystal structure. Due to the anisotropic chemical bonding, Mo2AlB2 has anisotropic thermal expansion coefficients αa = 6.19 × 10–6 K1, αb = 12.13 × 10−6 K–1, αc = 6.66 × 10−6 K–1, respectively, along a, b and c directions in the temperature range between 300 and 1500 K. The heat capacity from 300 to 1500 K can be described as Cp = 120.32 + 0.01648T − 2.597 × 106T−2 (J∙mol–1∙K–1). The elastic constants decrease almost linearly with temperature. The elastic constants representing the resistance to principle deformation (c11, c22 and c33) decrease in faster rates than those representing shear deformation resistance (c44, c55 and c66). Correspondingly, bulk and Young’s modulus decrease in faster rates than shear modulus. In light of the structure-property relations of Mo2AlB2, it is suggested that future damage tolerant ceramics can be designed by putting stiff covalent bonding units into soft metallic bonding box to obtain both high stiffness and quasi-ductility.

The study of gas X (X=H2O, CH4, O2) adsorbed low density poly(4-methyl-1-pentene) foam by molecular dynamics simulations

We use the molecular dynamics (MD) simulations to study the important properties of gas X (X = H2O, CH4, O2) adsorbed-poly(4-methyl-1-pentene) (PMP) and our results clarify that the H2O and CH4 molecules can increase the glass transition temperature (Tg) of PMP while O2 molecules can decrease the Tg of PMP. Moreover, all the jump values of MSD for pure PMP and gas-adsorbed PMP fall behind the corresponding Tg and demonstrate the hindrance of the chain segment motion is reduced at high elastic state. In addition, the calculated Young's modulus (E), Bulk modulus (K), Shear modulus (G) and Poisson's ratio (γ) indicate the CH4-adsorbed PMP system has a remarkable mechanical property and the K/G and Cauchy pressure (C12−C44) also present it has an outstanding ductility. Therefore, CH4-adsorbed PMP foam is considered as a promising candidate target in ICF experiment.

Elastic properties of α- and β-tantalum thin films

We comparatively study the elastic properties of the two existing polytypes of tantalum, α-Ta (ground state bcc structure) and β-Ta (metastable tetragonal structure), using density functional theory (DFT) calculations and thin film growth experiments. The lattice parameter and the single-crystal elastic constants cij for the two allotropic structures were computed using pseudo-potentials with generalized gradient approximation. Sound velocity measurements on single-phase, highly-textured (001) β-Ta and (110) α-Ta films deposited by magnetron sputtering were carried out using picosecond laser ultrasonic and Brillouin light scattering techniques, while hardness H and Young's modulus E were measured using nanoindentation. We found that the β-Ta phase is significantly harder (H~18.0 GPa) than α-Ta (H~10.3 GPa), while their elastic stiffness properties and Cauchy pressure p are similar, C33~285–310 GPa, E~ 188 GPa, p ~ 70–80 GPa, and agree well with the computed values. However, the out-of-plane shear modulus G of the β-Ta film is softer by 28% with respect to that of α-Ta film and DFT values (50 vs. 69 GPa). The present findings reveal that, contrarily to common claims, the β-Ta phase is not at all brittle but elastically and plastically deforms in a compliant way. Its toughness and elastic strain to failure ability is further comprehended from low G/B (0.205) and high H/E (≈0.1) ratios and the absence of radial cracks around indents, which suggests that β-Ta is also a suitable phase for use as wear-resistant coating in biomedical applications.

First–principle studies on the electronic structural, thermodynamics and elastic properties of Mg17Al12 intermediate phase under high pressure

As an intermediate phase in Mg-Al alloy, Mg17Al12 has an important role of hindering dislocation motion to strengthen grain boundaries. The influence of pressure on the structural properties, electronic structure, and mechanical properties of Mg17Al12 from 0 GPa to 8 GPa have been investigated by using first-principles calculations. As the pressure increases in the pressure range, Mg17Al12 intermediate phase stay thermodynamic stable. Based on first-principles calculations study, from band structure analysis, Mg17Al12 has strong metallic character, and the metallicity of this phase reduced due to applied pressure. Moreover, the ionic bond interaction between Mg and Al atoms increase with increasing pressure. Due to empirical criterion and Cauchy pressure, Mg17Al12 have a mechanically stable structure as well as brittleness property from 0 GPa to 8 GPa. Generally speaking, after theoretical study, the effect of pressure on Mg17Al12 improve its compression resistance and fracture resistance, the ability of resisting plastic deformation also becomes stronger. Moreover, appling pressure can weaken the brittleness of Mg17Al12. The study of its anisotropy also play an important rule in Mg-Al alloy grain boundary strengthening. Mg17Al12 exhibits anisotropy at 0 GPa to 8 GPa, and Mg17Al12 has the strongest stiffness along the 〈100〉 direction.

Phonon stability, electronic structure results, mechanical and thermodynamic properties of RbSbO3 and CsSbO3 perovskite oxides: Ab initio investigation

Cubic perovskite oxides RbSbO3 and CsSbO3 have been investigated for structural stability, electronic results, elastic, mechanical stability and thermodynamic results by most accurate density functional theory (DFT). The optimization has been completed using Local density approximation (LDA) and Generalized gradient approximation (GGA) within the scheme of Perdew, Burke and Ernzrhof (PBE). The ground state optimized results present minimum energy within GGA for both compounds. Band structure and density of state results both present the metallic nature for these compounds. The mechanical properties like Young's modulus, Bulk modulus etc. have been deduced from elastic values. RbSbO3 was found to have more resistance to compression as compared to strength CsSbO3. Both the materials were found to have brittle nature from Poisson's ratio (υ), Cauchy's pressure (C12–C44) and Pugh ratio (B/G) criteria. The melting temperature was calculated to be 2148 ± 300 K, 1746 ± 300 K, respectively for RbSbO3 and CsSbO3. Pressure and temperature variation has been used for calculation of thermodynamic parameters within quasi-harmonic Debye approximation. The nature of Bulk modulus, cell volume, specific heat capacity and thermal expansion has been computed in the temperature range of 0 K–900 K and pressure varied from 0 GPa to 15 GPa.

Effect of Al solute concentration on mechanical properties of AlxFeCuCrNi high-entropy alloys: A first-principles study

The elastic and plastic properties, generalized stacking-fault energy, surface energy, and electronic properties of AlxFeCuCrNi high-entropy alloys are studied via first-principle calculations. The present work is performed by employing density-functional theory within the general gradient approximation and virtual crystal approximation model. The increasing Al concentration enhances Young's modulus, bulk modulus and shear modulus, but it reduces the ductility based on the investigation of Cauchy pressure, ratio between shear modulus and bulk modulus, and Poisson's ratio. Besides, all AlxFeCuCrNi (0.1 ≤ x ≤ 1) high-entropy alloys are elastic anisotropic materials. In addition, the high Al concentration results in the large generalized stacking-fault energy and surface energy in AlxFeCuCrNi high-entropy alloys, which cause the possibility of dislocation nucleation and the inhibition of nanocrack formation.

Structural, elastic, mechanical, electronic, magnetic, thermoelectric and thermodynamic investigation of half metallic double perovskite oxide Sr2MnTaO6

Abstract Experimental lattice constant has been used for theoretical predictions on structural, elastic, mechanical, electronic magnetic thermoelectric and thermodynamic properties of Sr2MnTaO6 double perovskite oxide within well-known ab-initio density functional theory. Optimized lattice constant has been employed for obtaining spin involved electronic structure results within generalized gradient approximation (GGA), Hubbard approximation (GGA + U) and modified Becke Johnson approximation (mBJ). Electronic results show half-metallic nature with majority spin channels as metallic and minority spin channels as semi-conducting. Magnetic moment calculated within GGA + U was found equal to 4 µb. Calculated large value of Bulks modulus (B) and Young modulus (Y) characterize it as hard and stiffer material. Pugh ratio (B/G) and Cauchy pressure (C12–C44) portray its brittle nature. Using Boltztrap code we have calculated the variation of electrical conductivity (σ/τ), Seebeck coefficient (S), electronic thermal conductivity (k/τ) and Power factor (PF) in both spin channels. (σ/τ) is found to have decreasing nature in spin up states and increasing nature in spin down states, hence confirms the metallic nature in spin up states and semi-conducting in spin down states. Seebeck coefficients (S) reveal the presence of positive charge carriers in spin up states and negative in spin down states. The computed value of total power factor was found to be 1.99 × 1012 WK−2 m−1 s−1 at 1000 K. Furthermore, we have computed pressure and temperature dependent thermodynamic parameters for this compound in the temperature range of 0 K to 1000 K and pressure range of 0 GPa to 18 GPa with a step size of 3 GPa.

Phase stability and physical properties of (Zr1-xNbx)2AlC MAX phases

In this study, density functional theory (DFT) calculations were performed to investigate the key structural, elastic, mechanical, thermal, and electronic properties of the MAX phases of Zr2AlC and Nb2AlC, and particularly their solid solutions (Zr1-xNbx)2AlC, which are found to be thermodynamically stable. The partial inclusion of Nb in the M-site improves the bond strength and the hardness of Zr2AlC. The stiffness of (Zr1-xNbx)2AlC increases with the Nb-content x, and thus improves its ability to resist the shear deformation. With large negative Cauchy pressure, all of the compositions of (Zr1-xNbx)2AlC are predicted to exhibit directional covalent bonding. The composition with x = 0.2 is expected to be more brittle than the other compositions. The other properties including the anisotropy in elasticity, average sound velocity, Debye temperature (predicted to be highest for the composition with x = 0.4 in (Zr1.xNbx)2AlC), melting point, electronic structures, and Vickers hardness were examined. The covalency increases in (Zr1-xNbx)2AlC as the Nb-content x increases, which may explain the increase in the stiffness of the compositions.

MgCu2-type laves phases CaPt2, SrPd2 and SrPt2: A DFT based ab-initio investigation

First principle calculations have been performed to study the structural, elastic, electronic, Vickers hardness, optical and thermodynamic properties of Laves phase compounds CaPt2, SrPd2 and SrPt2for the first time. The optimized structural parameters such as lattice constants, unit cell volume and bulk modulus are well agreed with experimental values. The calculated elastic constants of all phases obey the well-known Born stability criteria and indicate the mechanical stability of CaPt2, SrPd2 and SrPt2. The calculated values of Cauchy pressure, Pugh's ratio and Poisson's ratio indicate the ductile nature of all three studied phases. The positive values of Cauchy pressure reveal the metallic nature of CaPt2, SrPd2 and SrPt2. The band structures show no band gap at the Fermi level which indicates the metallic nature of all these phases. The calculated total density of states (TDOS) of CaPt2, SrPd2 and SrPt2 are 3.90, 2.81 and 4.06 states per unit cell per eV respectively. These non-zero values of density of states at the Fermi level further indicate the metallic nature and the sequence of increasing metallic behavior is SrPd2< CaPt2< SrPt2. The detailed investigation of Mulliken atomic population indicates the covalent nature of PtPt and PdPd bonds because of the positive bond populations. The calculated values of Vickers hardness reveal that these phases are relatively soft materials. The various optical functions such as dielectric function, refractive index, conductivity, refractivity, absorption coefficient and loss function have also been investigated for the first time. The reflectivity spectra indicate that all studied phases are suitable to use as a good coating material in UV energy range. The calculated values of Debye temperatures are 271 K, 123 K and 230 K for CaPt2, SrPd2 and SrPt2 respectively. The melting temperature, Dulong-petit limit and thermal conductivity have also been calculated.

An ab-initio Investigation: The Physical Properties of ScIr2 Superconductor

Using ab initio technique the physical properties of ScIr2 superconductor have been investigated with Tc 1.03 K with a MgCu2-type structure. We have carried out the plane-wave pseudopotential approach within the framework of the first-principles density functional theory (DFT) implemented within the CASTEP code. The calculated structural parameters confirm a good agreement with the experimental and other theoretical results. Using the Voigt-Reuss-Hill (VRH) averaging scheme the most important elastic properties including the bulk modulus B, shear modulus G, Young’s modulus E and Poisson’s ratio ν of ScIr2 are determined. At ambient condition, the values of Cauchy pressure and Pugh’s ratio exhibit ductile nature of ScIr2. The electronic and optical properties of ScIr2 were investigated for the first time. The electronic band structure reveals metallic conductivity and the major contribution comes from Ir-5d states. In the ultraviolet region the reflectivity is high up to 50 eV as evident from the reflectivity spectrum.

First-principles calculations of the effect of Ge content on the electronic, mechanical and acoustic properties of Li17Si4-xGex

The electronic, mechanical and acoustic properties of Li17Si4-xGex (x = 0, 2.3, 3.08, 3.53, and 4) have been investigated by using first-principles calculations based on the density functional theory (DFT). The research shows that the bulk modulus B, Young's modulus E, shear modulus G, and hardness Hv gradually decrease with the increasing Ge content. Li17Si4-xGex have the brittle nature from the analysis of B/G ratio and Cauchy pressure. The maximum Young's moduli are all along [1 1 0] plane, and the sequence of degree of anisotropic property is Li17Ge4 > Li17Si0.48Ge3.52 > Li17Si0.92Ge3.08 > Li17Si1.7Ge2.3 > Li17Si4. The analysis of acoustic velocity shows that all the sound velocities decrease with the increasing Ge content for Li17Si4-xGex (x = 0, 2.3, 3.08, 3.53, and 4), and the longitudinal wave along [111] direction is fastest for the studied compounds. Debye temperature ΘD, vt and vl decrease with the increasing Ge content. The minimum thermal conductivity decreases with the increasing Ge content, and Li17Si4-xGex have low thermal conductivities and are not potential thermal conductors. The analysis of electronic properties indicates that Li17Si4-xGex have the metal nature and anisotropic electrical conductivity. The electric conduction is improved with the increasing Ge content.