Mechanical Stability Criteria Research Articles

Study of pressure induced physical properties of ZnZrO3 perovskite using density functional theory

The zinc zirconate ZnZrO3 perovskite have been studied with respect to their physical properties by inducing pressure upto20 GPa. The predicted value of lattice constant for ZnZrO3 determined using PBEsol-GGA is reasonable agreement with experimental value. Our calculations showed that Born mechanical stability criteria, confirmed the mechanical stability in cubic phase. Further, through Poisson and Pugh’s ratios critical limits, the findings of the ductile strength have been computed. To explore the pressure induced band structure modification, a varying external pressure from 0 GPa to 20 GPa has been applied with a step size of 5 GPa. The change in band structure significantly affected the optical properties of the material under study. It was observed that the band gap of ZnZrO3 shifted from indirect to direct at applied pressure of 15 GPa. The effect of this shifting on the dielectric constant, optical loss factor, reflection, refraction and absorption has been carried out in this work. To probe the potential of this composition for thermoelectric applications, its electrical conductivity, thermal conductivity, See-beck coefficient and power factor were also calculated.

Mechanical and electronic properties of van der Waals layered hcp PdH2

Mechanical and electronic properties of palladium dihydrides (PdH2) as a function of pressure were studied by ab initio calculations based on density functional theory (DFT). The ab initio random structure searching technique was employed for screening potential PdH2 crystal structures under high pressure. A hexagonal close packed (hcp) phase of PdH2 with space group P63mc was reported. The structure geometry and elastic constants were calculated as a function of pressure. It was found that H atoms are in the interstitial position of Pd atoms layer at 0 GPa. There is an electronic topology transition of hcp PdH2 at 15 GPa. When pressure exceeds above 15 GPa, one hydrogen atom occupies the tetrahedral site and another hydrogen atom locates in the interstitial position. When the c/a ratio is between 1.765 to 1.875, the hcp PdH2 is mechanically stable, and the Pd-H2b bond is the major factor that limits the mechanical stability. The elastic constant C44 is the first one that cannot satisfy the mechanical stability criteria under pressure. The anisotropy parameters are far from 1(one) shows that the hcp PdH2 is a highly anisotropic structure. The electronic structure study indicates that the bonding force between Pd and H atoms along the z-axis direction increases with the increasing pressure. Also, the phonon dispersion study shows that PdH2 is dynamic stability under pressure. The results suggest that hcp PdH2 can be metastable in van der Waals layered structure.

Theoretical investigations of optoelectronic and thermoelectric properties of the XIn2O4 (X = Mg, Zn, Cd) spinel oxides

The spinel oxides have received remarkable attention in recent years for being promising materials for optoelectronic and thermoelectric applications. In this paper, the thermodynamic stability of the XIn2O4 (X = Mg, Zn, Cd) spinels is examined by calculating the formation energy whereas the mechanical stability is evaluated by Born mechanical stability criteria. Our results indicate adequate thermodynamic and mechanical stability of the studied spinels. Ductile behavior of these materials is established through Pugh's and Poisson's ratios. The bandgaps of magnitudes 4.0 eV, 2.79 eV, and 2.21 eV have been calculated respectively for MgIn2O4, ZnIn2O4 and CdIn2O4 by modified Becke and Johnson (mBJ) exchange potential. The optical spectra of dielectric constants, refraction, absorption and other related parameters are determined to explore their potential for optoelectronic applications. Furthermore, thermoelectric properties are investigated in terms of thermal to electrical conductivities, Seebeck coefficients, and figures of merit (ZT). The high ZT of magnitude 0.84, 0.74, 0.79 are observed for MgIn2O4, ZnIn2O4 and CdIn2O4 that highlight important of these materials' potential applications in thermoelectric generators and other thermal energy conversion devices.

Structural, electronic, magnetic, elastic and thermodynamic properties of [formula omitted] perovskite

In this paper, we have studied the structural, electronic, magnetic, elastic and thermodynamic properties of the cubic perovskite system Cr4N using the first-principles calculations based on density functional theory (DFT) with the generalized gradient approximation (GGA). Our results show that the Cr4N is more stable in a ferrimagnetic configuration (FIM) and in a ferromagnetic arrangement (FM), Cr4N is nonmagnetic compound (NM). Density of States (DOS) and band structure calculations show a metallic behavior of Cr4N. The calculated elastic constants satisfy the Born mechanical stability criterion. Based on the calculated data of Poisson’s ratio, Cr4N have ionic bonding. According to the B/G values, the compound under investigation is found to be brittle nature in FIM configuration and ductile nature in FM and NM configurations. The exchange interactions of Cr4N, were calculated to obtain the critical temperature (TC) from Monte Carlo calculations. The obtained value of TC (295 K) is in good agreement with other theoretical works.

Investigation of the Mechanical, Electronic and Phonon Properties of X2ScAl (X = Ir, Os, and Pt) Heusler Compounds

In the present study, the second-order elastic constants and the electronic band structures of the X2ScAl (x = Ir, Os, and Pt) compounds crystallized in the L21 phase were calculated separately by using the ab-initio density functional theory. According to the results for the second-order elastic constants, these compounds met the Born mechanical stability criteria. Also, according to the Pugh criteria, they were found to have a ductile structure and to show anisotropic behavior. The microhardneses of the compounds were between 2 and 14 GPa, and the highest hardness was found in the Ir2ScAl (14.290 GPa) compound. In addition, the energy band structures of these compounds were calculated, and the crystals were found to have a metallic bond structure. All the computed data were compared with previously calculated results obtained with different methods. According to the findings obtained in the present study, in terms of its mechanical and electronic behaviors, Ir2ScAl was found to have better physical properties than Os2ScAl and Pt2ScAl. The phonon dispersion curves and their corresponding total and projected densities of states were investigated for the first time by using a linear-response approach in the context of density functional perturbation theory. The frequencies of the optical phonon modes of all compounds at the Γ point were 4.767, 7.504 and 9.271 THz for Ir2ScAl, 2.761, 7.985 and 9.184 THz for Os2ScAl and 2.012, 5.6952 and 8.118 THz for Pt2ScAl. The heat capacity Cv at constant volume versus temperature was calculated using a quasi-harmonic approach and the results are discussed.

The stability, electronic, mechanical and thermal properties of three novel superhard carbon crystals

Three novel orthorhombic carbon crystals were designed and their stability, sound velocities, thermal conductivity and dynamically and mechanical properties were investigated. Density functional theory calculations show that the three carbon crystals are energetically stable with cohesive energies less than −8.94 eV and their elastic constants satisfy the mechanical stability criterion of orthorhombic system. They are anisotropic superhard materials with Vickers hardness of over 79 GPa based on four different models. Their Debye temperature are over 2100 K, only a little lower than that of diamond. The calculations show that they may be synthesized from cold-compressed graphite under pressure of less than 20 GPa. Their similar structural features to diamond and excellent mechanical performance suggest that diamond can be a useful structural template of superhard materials.

First Principles Study on the Thermodynamic and Elastic Mechanical Stability of Mg2X (X = Si,Ge) Intermetallics with (anti) Vacancy Point Defects

In this paper, based on the density functional theory, through thermodynamic and mechanical stability criteria, the crystal cell model of intermetallic compounds with vacancy and anti-site point defects is constructed and the lattice constant, formation heat, binding energy, elastic constant, and elastic modulus of Mg2X (X = Si, Ge) intermetallics with or without point defects are calculated. The results show that the difference in the atomic radius leads to the instability and distortion of crystal cells with point defects; Mg2X are easier to form vacancy defects than anti-site defects on the X (X = Si, Ge) lattice site, and form anti-site defects on the Mg lattice site. Generally, the point defect is more likely to appear at the Mg position than at the Si or Ge position. Among the four kinds of point defects, the anti-site defect x M g is the easiest to form. The structure of intermetallics without defects is more stable than that with defects, and the structure of the intermetallics with point defects at the Mg position is more stable than that at the Si/Ge position. The anti-site and vacancy defects will reduce the material’s resistance to volume deformation shear strain, and positive elastic deformation, and increase the mechanical instability of the elastic deformation of the material. Compared with the anti-site point defect, the void point defect can lead to the mechanical instability of the transverse deformation of the material and improve the plasticity of the material. The research in this paper is helpful for the analysis of the mechanical stability of the elastic deformation of Mg2X (X = Si, Ge) intermetallics under the service condition that it is easy to produce vacancy and anti-site defects.

The structural, electronic, elastic and high thermoelectric properties of a new Zintl compound Ba<sub>3</sub>Sn<sub>3</sub>Sb<sub>4</sub> studiedby first principles

The structural, electronic, elastic, and thermoelectric properties of a new recently synthetized Zintl compound Ba3Sn3Sb4 are studied using the first principles and the Boltzmann theory. We determine the requirements of the chemical potentials for the formation of Ba3Sn3Sb4. On the basis of the mechanical stability criteria and the phonon spectrum of Ba3Sn3Sb4, the lattice structure is determined to be thermodynamically stable. The electron density difference of Ba3Sn3Sb4 shows that there is an ionic bond between Ba and the [Sn3Sb4] cluster, and a covalent Sn–Sb bond in [Sn3Sb4]. The coexistence of ionic and covalent bonds indicates that Ba3Sn3Sb4 is a typical Zintl compound. The calculated electronic band structure shows that Ba3Sn3Sb4 is an indirect semiconductor with a band gap ~0.29 eV. In the conduction bands, the presence of multivalley bands benefits the thermoelectric properties. In terms of the Slack model, the lattice thermal conductivity κ l is smaller than 0.5 W m−1 K−1 when the temperature is over 720 K. On the basis of the analysis of the band structure, we calculate the thermoelectric properties using the Boltzmann theory. The results show that p-type-doped Ba3Sn3Sb4 undergoes interesting changes. Because pristine Ba3Sn3Sb4 is an n-type semiconductor, the Seebeck coefficient of p-type-doped Ba3Sn3Sb4 changes from negative to positive at T =500 K or T =700 K. For p-type-doped Ba3Sn3Sb4, the calculated largest ZT is 0.09. For n-type-doped Ba3Sn3Sb4, the Seebeck coefficient exhibits bipolar effects at T >500 K. This result is obtained because thermal excitation becomes strong with an increase in the temperature, and the effect of the minor carriers leads to the change of the S value. The optimized largest ZT value of n-type-doped Ba3Sn3Sb4 is up to 0.26 with n =1.14×1020 cm−3 at T =700 K, which is almost three times that of p-type-doped Ba3Sn3Sb4.

Robust stability, half-metallic ferrimagnetism and thermoelectric properties of new quaternary Heusler material: A first principles approach

Like full or half-heusler materials, equiatomic quaternary Heuslers (EQH) also display various intriguing physical properties. We carried out the strict and rigorous density functional theory calculations to estimate the stability of novel ferrimagnetic FeMnTaAl alloy. In this work, we considered the thermodynamic, energetic, dynamic and mechanical stability criteria, by evaluating the formation energy, phonon dispersion and elastic constants, respectively, which thereby suggest that the synthesis of FeMnTaAl as bulk phase is likely. Later, the electronic structure, magnetic and transport properties are determined from the ground state parameters. After the structural optimizations, the half-metallic character from spin resolved band structures and local spin moments (1 μB) potentially felicitate its spintronic applications. Conservative estimates of Seebeck coefficient (~85 μV/K at 900 K), lattice thermal conductivity (2.8 W/mK at 300 K) and figure of merit (0.03 at 900 K) have also been put forward in this report. The overall structural stability, ferrimagnetism with large TC accompanied by transport properties will possibly enact the experimental realization for magnetic, thermoelectric or spintronic impressions of this material in future.

Recently synthesized (Ti1-x Mo x )2AlC (0 ≤ x ≤ 0.20) solid solutions: deciphering the structural, electronic, mechanical and thermodynamic properties via ab initio simulations.

The structural, electronic, mechanical and thermodynamic properties of (Ti1−xMox)2AlC (0 ≤ x ≤ 0.20) were explored using density functional theory. The obtained lattice constants agree well with the experimental values. The electronic band structure confirms the metallic nature. Strengthening of covalent bonds due to Mo substitution is confirmed from the study of band structure, electronic density of states and charge density mapping. The elastic constants satisfy the mechanical stability criteria. Strengthening of covalent bonds leads to enhanced mechanical properties. (Ti1−xMox)2AlC compounds are found to exhibit brittle behavior. The anisotropic nature of (Ti1−xMox)2AlC is revealed from the direction dependent Young's modulus, compressibility, shear modulus and Poisson's ratio as well as the shear anisotropic constants and the universal anisotropic factor. The Debye temperature, minimum thermal conductivity, Grüneisen parameter and melting temperature of (Ti1−xMox)2AlC have been calculated for different Mo contents. Our calculated values are compared with reported values, where available.

Low compressible β-BP3N6

Using first principles calculation, the structural and mechanical properties of β-BP3N6, which adopts an orthorhombic structure with space group Pna21 (no. 33), were determined at three different pressure values (0, 20, and 42.4 GPa). The nine independent elastic constants meet all necessary and sufficient conditions for mechanical stability criteria for an orthorhombic crystal. β-BP3N6 shows strong resistance to volume change and hence a potential low compressible material. The Vickers hardness of β-BP3N6 was found to range between 49 and 51 GPa for different external pressures imposed on the crystal. These high values of Vickers hardness imply that β-BP3N6 is a potential superhard material.

Phase stability, magnetic and elastic properties of Co2NiGa alloy: A first-principles calculation

The phase stability, magnetic and elastic properties of Co2NiGa high temperature shape memory alloy were systematically investigated by the first-principles calculations. A new configuration was proposed for the parent phase of the stoichiometric Co2NiGa alloy. The elastic constants of this new structure satisfy the criteria of mechanical stability. The formation energies of the stoichiometric Co2NiGa in the paramagnetic austenite (PA), ferromagnetic austenite (FA) and non-modulated (NM) martensite were calculated. The bulk modulus, Young’s modulus and shear modulus of Co2NiGa alloys are higher than those of the Ni2MnGa alloy, which can provide larger deformation resistance.

First-principles calculations of mechanical and thermodynamic properties of tungsten-based alloy

Abstract The structural, mechanical and thermodynamic properties of tungsten-based alloys, including W0.5Ti0.5,W0.67Zr0.33,W0.666Ti0.1667Zr0.1667,W0.67Hf0.33 and W0.666Ti0.1667Hf0.1667, have been investigated in this paper by first-principles calculations based on density functional theory (DFT). The calculated elastic constants and mechanical stability criteria of cubic crystals indicated that all of these cubic alloys are mechanical stable. The mechanical properties, including bulk modulus (B), shear modulus (G), Young’s modulus(E), ratio B/G, Poisson’s ratio, Cauchy pressure and Vickers hardness are derived from the elastic constants Cij. According to calculated elastic modulus and Vickers hardness, the W0.666Ti0.1667Hf0.1667 alloy has the greatest mechanical strength. The Vickers hardness of these cubic alloys rank as follows: W0.666Ti0.1667Hf0.1667 > W0.67Zr0.33 > W0.666Ti0.1667Zr0.1667 > W0.5Ti0.5 > W0.67Hf0.33. Moreover, calculated ratio B/G, Poisson’s ratio, Cauchy pressure indicated that the ductility of W0.666Ti0.1667Hf0.1667 alloy is the worst among these alloys. The ductility of these cubic alloys rank as follows: W0.67Hf0.33 > W0.5 Ti0.5 > W0.67Zr0.33 > W0.666Ti0.1667Zr0.1667 > W0.666Ti0.1667Hf0.1667. What is noteworthy is that both mechanical strength and ductility of W0.666Ti0.1667Hf0.1667 are greater than pure W. Finally, Debye temperature, melting point and thermal conductivity have been predicted through empirical formulas. All these results will provide scientific data for the study on new product development of electrode materials.

Tuning the electronic structures and transport coefficients of Janus PtSSe monolayer with biaxial strain

Due to their great potential in electronics, optoelectronics, and piezoelectronics, Janus transition metal dichalcogenide monolayers have attracted an increased interest in research, and the MoSSe monolayer of them with the sandwiched S-Mo-Se structure has been synthesized experimentally. Here, we systematically study the effect of strain on electronic structures and transport properties of the Janus PtSSe monolayer. A detrimental effect on the power factor of the PtSSe monolayer can be observed when the spin-orbital coupling is included. With a/a0 from 0.94 to 1.06, the energy bandgap shows a nonmonotonic behavior, which is due to the position change of conduction band minimum. The strength of conduction bands convergence can be enhanced by changing the relative position of conduction band extrema caused by compressive strain, which is in favor of the n-type ZTe. Calculated results show that compressive strain can also induce flat valence bands around the Γ point near the Fermi level, which can lead to a high Seebeck coefficient due to large effective masses, giving rise to better p-type ZTe values. The calculated elastic constants with a/a0 from 0.94 to 1.06 all satisfy the mechanical stability criteria, which proves that the PtSSe monolayer is mechanically stable in the considered strain range. Our works provide a new route to tune the electronic structures and transport coefficients of the Janus PtSSe monolayer by biaxial strain and can motivate related experimental studies.

Theoretical predictions of magnetic shape memory alloys in Gallium-rich Heusler compounds

This paper provides a comprehensive study of the structural, magnetic, electronic, vibrational, and bulk mechanical properties for Ga2(Nb,Ta,W)X (X = Cr, Mn, Fe, Co, and Ni) Heusler alloys using first-principles density-functional theory. By considering the total energy, the structural type and magnetic configuration of cubic Ga2(Nb,Ta,W)X are determined. Analyzing the calculated formation energies allows determination of the compounds that are stable electronically. The total energy difference between the austenite and martensite phases indicates that all the alloys are prone to tetragonal transitions from the austenite to martensite phases. Furthermore, the martensitic transitions are demonstrated from the perspectives of the density of states, phonon dispersion, mechanical stability criteria, and elastic anisotropy ratio. The ratio of the shear to bulk moduli indicates that all the considered Ga2-based materials are inherently ductile, and most of the alloys possess much better ductility than the well-known Ni2MnGa material. Among the considered alloys, Ga2(Nb,Ta)X (X = Cr, Mn, and Fe) and Ga2WX (X = Cr, Mn, Fe, and Co), which have martensitic transition temperatures above room temperature, are expected to operate as new magnetic shape memory alloys.

Mechanical and thermodynamic properties of two-dimensional monoclinic Ga2O3

The discovery of two-dimensional (2D) Ga2O3 has provided an efficient way to design high performance Ga2O3 devices. Here, mechanical and thermodynamic properties of 2D Ga2O3 are important parameters in device design but very few studies are investigated by density functional theory. Results show that 2D Ga2O3 retains the monoclinic character with thirteen independent elastic constants which meet with the mechanical stability criteria, and irrespective of its thickness. Interestingly, although the elastic constant C11 is lower than C22 and C33, 2D Ga2O3 may be harder to be compressed along the a direction. Meanwhile, the elastic constant C44 is larger than C55 and C66, in contrast to that of bulk β-Ga2O3. Upon decreasing the thickness of 2D Ga2O3, the elastic properties continue reduce and lower than those of 2D layered materials, but their compressive anisotropic properties are enhanced and larger than those of bulk β-Ga2O3. The thermal conductivity and capacity of monolayer Ga2O3 are enhanced to 0.49 W∙cm−1∙K−1, and 27.58 J∙mol−1∙K−1, respectively. Such variations of bulk-transition-2D Ga2O3 are opposite to those of bulk-transition-2D GaN due to the recombined orbitals of GaN. These results are crucial to the device design based on 2D Ga2O3.

Structural, magnetic, electronic and elastic properties of half-metallic ferromagnetism full-Heusler alloys: Normal-Co2TiSn and inverse- Zr2RhGa using FP-LAPW method

The equilibrium structural parameters, electronic, magnetic and elastic properties of the inverse Zr2RhGa and normal Co2TiSn Full-Heusler compounds have been studied using density-functional theory (DFT) and full-potential linearized augmented plane-wave (FP-LAPW) method as implemented in the WIEN2k package. The Generalized Gradient Approximation (GGA) has been used for the exchange-correlation potential (Vxc) to compute the equilibrium structural parameters; lattice constant (a), bulk modulus (B) and bulk modulus pressure derivative (B′). In addition to the GGA approach, the modified Becke Johnson (mBJ) scheme has been used to calculate the band gap energies. The normal Heusler Co2TiSn compound and the inverse Heusler Zr2RhGa compound within GGA and mBJ approaches are found to have a half-metallic behavior, with an indirect energy gap in the spin down configuration. The calculated total magnetic moments for both compounds are to some extent compatible with the available experimental and theoretical results. Elastic constants and their related properties were obtained by using the IRelast package. These compounds are mechanically stable. The elastic constants satisfy the Born mechanical stability criteria. B/S ratio shows that the normal Co2TiSn has a brittle nature, while the inverse Zr2RhGa has a ductile nature; Poisson's ratio (ν) values show that both compounds have an ionic bond nature.

Structural, elastic and electronic properties of new superhard orthorhombic C28

The structural, mechanical and electronic properties of recently reported superhard material C[Formula: see text] are studied by first-principles calculations. The unit cell of C[Formula: see text] is composed of 28 carbon atoms and all sp3 hybridized bonds. From 0 GPa to 100 GPa, C[Formula: see text] satisfies the mechanical stability criteria and the phonon spectrum of C[Formula: see text] has no imaginary frequency, which means that C[Formula: see text] is mechanically and dynamically stable. The results of hardness calculated show that C[Formula: see text] is a potential superhard material with the Vickers hardness of 84.0 GPa. By analyzing the elastic anisotropy, we found that elastic anisotropy of C[Formula: see text] increases with pressure. The calculations of band structure demonstrates that C[Formula: see text] is an indirect bandgap semiconductor with the gap of 4.406 eV. These analyses demonstrate C[Formula: see text] is a superhard semiconductor material.

Theoretical investigation of elastic constants and related properties of compressed PbO2

This work aims to study the structural and elastic properties of tetragonal lead dioxide (β-PbO2) material using first-principles calculations. Features such as lattice parameters, bulk modulus and its first pressure derivative, elastic constants, mechanical parameters, sound velocities, Debye temperature and melting temperature have been investigated, and their dependence on pressure in the range 0–1 GPa has been analyzed and discussed. Upon compression, the stiffness of the material of interest is found to become larger as compared to that at zero pressure. Moreover, its tetragonal structure fulfills the mechanical stability criteria in all studied pressure range. Besides, the analysis of Pugh’s ratio shows that PbO2 behaves in a ductile manner.

Halfmetallicity, mechanical and thermodynamic study on iridium based compounds by First Principles calculations

Using First Principles calculations as implemented in Wien2K, Electronic structure, Magnetic, Half-Metallic, Mechanical and thermodynamic properties has been studied for Ir2MnAl and Ir2MnGa full Heusler alloys. Structural optimization was performed for nonmagnetic (NM), Ferromagnetic (FM) and antiferromagnetic (AFM) states using LSDA as exchange-correlation potential. Both the alloys were found to be stable in FM states. These alloys have satisfied Born mechanical stability criteria in ferromagnetic L21 structure. Elastic constants, Mechanical properties, and thermodynamic properties were calculated. They reveal that these alloys being incompressible, ductile and anisotropic. Ir2MnAl exhibited half metallicity with 100% spin polarization, while, Ir2MnGa was observed to be metallic with 96% spin polarization. The total spin magnetic moment per unit cell of both the alloys satisfy Slater-Pauling rule with 4 μB and 4.02 μB for Ir2MnAl and Ir2MnGa respectively. Ir2MnAl was observed to be a half-metallic ferromagnet with an indirect energy gap of 0.25eV. Curie temperature was calculated using the mean field approximation method to be 110K for Ir2MnAl. Since the calculated value of Curie temperature is low, Ir2MnAl, would not be suitable for room temperature spintronic devices.