Mechanical Stability Criteria Research Articles

First-principles calculations to investigate thermodynamic, mechanical and electronic properties of Penta-C72 carbon under pressure effect

The current work explores the mechanical characteristics, band structure modifications, elastic constant changes, and anisotropy of the carbon allotrope Penta-C72 at high pressure. First-principles simulations were used to analyse the structural features, stability, electronic, mechanical, and thermodynamic properties of Penta-C72, a metastable sp3 -bonded structure made up of carbon pentagons joined by bridge-like connections. The structural and dynamical stability of Penta-C72 under high pressure is confirmed using formation energy, phonon band maps, and thermodynamic properties. Besides, Born's mechanical stability criterion is fulfilled based on the elastic constants of Penta-C72, indicating its mechanical stability. Also, the anisotropic mechanical behaviour is shown by the material. Using the Reuss, Voigt, and Hill approximations, the elastic moduli under high pressure were computed, including bulk modulus (K), shear modulus (G), and Young's modulus (E). Besides, Penta-C72 exhibits a rise in anisotropy and moduli with increasing pressure. This investigation explores the changes in the band gap upon variation in the pressure. It is observed that there is a transition from semiconducting to metallic property above 10 GPa. Beyond 10 GPa, the material exhibits metallic behaviour. The study emphasizes that Penta-C72’s exceptional mechanical stability, directional anisotropy, and customisable electronic characteristics make it a strong contender for various engineering applications.

First-principles calculations of phase transition, phonon spectra, thermodynamic properties and elasticity for PuO2 polymorphs

The first principles are utilized to calculate the phase transition, phonon spectra, thermodynamic properties, and elasticity of PuO2 under varying pressures. Under the compression condition, the anticipated pressure of phase transition from Fmm to Pnma is 26.7 GPa, from Pnma to Cmcm is 112.9 GPa, and from Cmcm to I4/mmm phase is 588.0 GPa. As the pressure decreases, the phase transition pressure of anticipating from Fmm phase to P42/mnm phase occur at -8.6 GPa. The phonon spectra of these six structures show that all phases are dynamically stable under the selected pressure. Meanwhile, the verification results of the mechanical stability criterion show that Fmm, Pnma, Cmcm and I4/mmm of PuO2 are mechanically stable, nevertheless P42/mnm is unstable in high pressure. The thermodynamic properties were then calculated to further research the patterns of variation in the coefficient of thermal expansion, bulk modulus, Gibbs free energy, and heat capacity with temperature, and these were compared with experimental data.

Effect of Ti doping on phase stability and half-metallicity of the Co2FeGe compound: GGA and mBJ-GGA approaches

Density Functional Theory (DFT) calculations were performed using the full-potential linearized augmented plane wave (FP-LAPW) method to study the effect of Ti doping on Co2FeGe systems. The both GGA and mBJ-GGA formalisms were employed in this study. For both the L21 and XA structures, ferromagnetic, ferrimagnetic and paramagnetic phases were considered, and lattice optimization was conducted to determine the most stable magnetic phase. The Co2FeGe and Ti2FeGe Heusler alloys were found to be stable in the ferromagnetic state with the L21 structure. In contrast, the XA-type ordering was observed for the CoTiFeGe alloy. The density of states and band structure calculations for the CoTiFeGe (XA structure) alloy revealed half-metallic behavior, which is notable for its potential in achieving high spin polarization. Additionally, half-metallic character was observed for the Co2FeGe alloy with L21-type ordering when using the mBJ-GGA formalism. The calculated elastic constants confirmed that these systems satisfy the mechanical stability criteria. Furthermore, the systems with x = 0.00 (Co2FeGe) and x = 1.00 (Ti2FeGe) comply with the Slater-Pauling rule for half-metallicity in alloys, given by Mtot = NV-24. According to the mBJ-GGA method, the total magnetic moments of Co2FeGe and CoTiFeGe are 6 μB and 1 μB, respectively. Meanwhile, the Ti2FeGe compound follows the condition Mtot = NV-18 and has a total magnetic moment of approximately 2 μB. The optoelectronic properties were examined through analysis of the optical constants, confirming semiconducting behavior for both x = 0.00 and x = 1.00.

First-principles calculations to investigate optoelectronic of transition-metal half-Heusler alloys MTiSn (M = Pd and Pt) for optoelectronics applications

The structural, mechanical, optical, and electronic properties of half-Heuslers MTiSn (M = Pd and Pt) are investigated using FP-LAPW incorporating the GGA-PBE. MTiSn crystallize in ferromagnetic (FM) and cubic structure (F-43m; C1b) with lattice constants of 6.216 Å and 6.241 Å, respectively, in good agreement with the available data. Elastic constants Cij reveal that MTiSn meet the mechanical stability criteria with notable thermodynamic properties. Also, we have conducted a detailed analysis of optical properties, encompassing the dielectric function, absorption coefficient, optical conductivity, optical refractivity, and extinction coefficient. It is found that PtTiSn shows higher optical responses than PdTiSn at low and high energy ranges. In terms of electronic properties, MTiSn demonstrate narrow bandgap semiconductor characteristics with an indirect bandgap of Eg = 0.507 eV (M = Pd) and Eg = 0.782 eV (M = Pt). The notable optoelectronic responses have also been examined, indicating the high potential of MTiSn materials for optoelectronic applications.

Investigation on the structural, elastic, electronic, thermodynamic, and vibrational properties of the full heusler Sc2XAl (X =Cd and Zn): An ab initio study

The structural, mechanical, electronic, thermodynamic, and phonon characteristics of Sc2CdAl and Sc2ZnAl in L21 phase were the main focuses on this investigation. The density of states (DOS) and electronic band spectra signify the metallic behavior of the L21 phase of both materials. The impact of atomic arrangement with respect to the Wyckoff sites on the mechanical stability were additionally studied. The elastic constants of Sc2CdAl and Sc2ZnAl alloys indicated that these alloys convened Born mechanical stability criteria. Using the density functional perturbation theory's first-principle linear response method, complete phonon spectra have been acquired. Moreover, the quasi-harmonic approximation, specific heat capacity at constant volume, the internal free energy, entropy, and vibrational free energy variations of Sc2CdAl and Sc2ZnAl as full Heusler alloys have been utilized in examination the change over the temperature between 0 and 800 K. Both alloys might find application in real industrial applications.

Properties of bismuth based Bi2A3 (A = S, Se, Te) chalcogenides for optoelectronic and thermoelectric applications

Structural, electronic, optical, mechanical, thermoelectric and dielectric properties of binary Bi2A3 (A = S, Se, Te) chalcogenide semiconductors are studied by first-principles approach. Bismuth sulfide (Bi2S3) is found to be structurally stable in orthorhombic structure while bismuth selenide (Bi2Se3) and bismuth telluride (Bi2Te3) are stable in trigonal structure. Calculated mechanical properties reveal that all three Bi2A3 (A = S, Se, Te) compounds fulfil the mechanical stability criteria. Band structure calculations reveal that the Bi2S3 exhibits direct optical band gap (Eg = 1. 58 eV) which lies in the near-infrared (NIR) region, while the calculated Eg of Bi2Se3 and Bi2Te3 are found to be 0.53 eV and 0.35 eV, respectively lying in the far-infrared region. For Bi2S3 and Bi2Se3 compounds, the calculated dielectric properties show strong anisotropic behavior, while negligible anisotropic dielectric behavior is observed for Bi2Te3. Calculated optical properties show that all three Bi2A3 compounds possess high absorption coefficient (> 104 cm−1). For all three Bi2A3 (A = S, Se, Te) compounds, the calculated optical conductivity show prominent peak corresponding to the occurrence of optical conduction at energies 3.36 eV, 2.65 eV and 2.02 eV respectively. Calculated optical results support the results deduced from band structures and density of states spectra. Optical properties and dielectric behavior suggest that the Bi2S3 compound has suitable band gap and has potential to use for photovoltaic applications while Bi2A3 (A = Se, Te) compounds could be used in infrared detectors and other optical devices. Calculated thermal properties reveal that the Bi2A3 (A = S, Se, Te) chalcogenides could be potential materials for thermoelectric applications.

Effect of V-VIB group ternary elements on the properties of Ti2AlM-type O-phases: A first-principles study

Understanding the underlying constitutional mechanisms for the stability of complex phases and comprehending it is crucial to find new materials with desired mechanical and physical properties. In TiAl-alloys with ternary alloying additions orthorhombic phases can form but the effects of different alloying elements on their stability and other properties are only scarcely known. We present a comprehensive study using density functional theory (DFT) within the generalized gradient approximation (GGA) with the Perdew–Burke–Ernzerhof (PBE) method to determine energetic, and mechanical stability criteria and evaluate the electronic densities of states (DOS) and band structures to understand bonding behavior. The stability of Ti2AlM, as a bulk O-phase in ternary TiAl-based systems is predicted by investigating VB (V, Nb, and Ta) and VIB (Mo, W) group elements as ternary addition M. The electronic density of states and band structure indicate that the ternary elements addition causes charge redistribution through the formation of a bond, which significantly alters the stability and mechanical properties. All investigated compounds exhibit negative formation energies and the calculated elastic constants reveal that all are mechanically stable. For the different O-phase types investigated Ti2AlMo is the most stable and Ti2AlV the least stable when comparing energies of formation. The obtained elastic moduli and Pugh's ratios support the idea that Ti2AlM (M = V, Nb, Ta, Mo, and W) O-phases have attractive mechanical characteristics and exhibit ductility. Among all the systems investigated, Ti2AlMo, and Ti2AlW provide the highest increase in B, G, and E values. Based on the elastic constants also indicators for the mechanical properties, such as Poisson's ratio (ν), and Pugh ratio G/B, are calculated. According to our calculations, the brittle Ti2AlV is harder than the ductile Ti2AlMo. Based on the results of the present study, the Ti2AlM type O-phase is considered a promising constituent for designing new materials in the ternary Ti–Al-M system.

A First-Principles Study of the Structural, Elastic, and Mechanical Characteristics of Mg2Ni Subjected to Pressure Conditions

This study employs first-principles calculations to examine structural, elastic, and mechanistic relationships of Mg2Ni alloys under varying conditions of pressure. The investigation encompasses Young’s modulus, bulk modulus, shear modulus, Poisson’s ratio, and anisotropy index, as well as sound velocity, Debye temperature, and related properties. Our findings indicate that the lattice parameters of Mg2Ni in its ground state are in agreement with values obtained experimentally and from the literature, confirming the reliability of the calculated results. Furthermore, a gradual decrease in the values of the lattice parameters a/a0 and c/c0 is observed with increasing pressure. Specifically, the values for C13 and C33 decrease at a hydrostatic pressure of 5 GPa, while C11 and C13 increase when the external hydrostatic pressure exceeds 5 GPa. All other elastic constants exhibit a consistent increasing trend with increasing pressure between 0 and 30 GPa, with C11 and C12 increasing at a faster rate than C44 and C66. In the 0–30 GPa pressure range, Mg2Ni satisfies the mechanical stability criterion, indicating its stable existence under these conditions. Additionally, the Poisson’s ratio of Mg2Ni consistently exceeds 0.26 over a range of pressures from 0 to 30 GPa, signifying ductility and demonstrating consistency with the value of B/G. The hardness of Mg2Ni increases within the pressure range of 0–5 GPa, but decreases above 5 GPa. Notably, the shear anisotropy of Mg2Ni exhibits greater significance than the compressive anisotropy, with its anisotropy intensifying under higher pressures. Both the sound anisotropy and the Debye temperature of Mg2Ni demonstrate an increasing trend with rising pressure.

Pressure and atomic size effects of IV cation on mechanical and electronic properties of Zn-IV-N2 (IV[dbnd]Si, Ge and Sn): First principles calculation

Zn-IV-N2 compounds, incorporating Si, Ge, and Sn, have emerged as pivotal materials for their mechanical and electronic properties, influencing optoelectronic devices and photovoltaic applications. Employing density functional theory (DFT), we comprehensively investigate the structural, elastic, mechanical, and electronic characteristics of ZnIVN2 (IVSi, Ge, Sn) under ambient and pressure conditions up to 20 GPa. Our findings suggest that a larger atomic size of the group IV cation can be more easily compressed than a smaller size. The mechanical stability criteria and the phonon dispersion show mechanical and dynamic stability in both ambient pressure and under high pressure up to 20 GPa. The ZnSiN2 and ZnGeN2 exhibit linear increments in bulk modulus (B), shear modulus (G), and Young's modulus (E) under pressure, while ZnSnN2 experiences a decrease in G and E. Notably, the energy gap of ZnSiN2, ZnGeN2, and ZnSnN2 (4.62 eV indirect, 2.82 eV, 1.16 eV, respectively) increases with pressure due to higher N s orbital energy, approaching the UV region. In the valence band, a hybridization of N p and Si/Ge/Sn p orbitals is observed, offering opportunities to tailor the band gap for optimal applications in optoelectronic devices. Preferentially adjusting group-IV elements over group-II elements is recommended for optimizing band gap modulation. The correlation between larger atomic size and decreased band gap energy highlights the potential to fine-tune material properties through controlled variations in group-IV elements.

Structural, electronic, mechanical, thermodynamic and optical properties of oxide perovskite BeZrO3: a DFT study

The geometrical, electronic, mechanical, thermodynamic, and optical aspects of BeZrO3 crystal have been investigated employing Generalized Gradient Approximation (GGA) with Perdew–Burke–Ernzerhof (PBE), Revised Perdew–Burke–Ernzerhof (RPBE), Local density approximation (LDA) with Ceperley Alder and Perdew Zunger (CA-PZ) techniques under density functional theory. The band gap values of BeZrO3 have been reported to be 0.603 eV, 0.623 eV, 0.614 eV and 2.20 eV respectively in PBE, RPBE, LDA and Becke, 3-parameter, Lee–Yang–Parr (B3LYP) methods. Total and partial density analysis was used to determine atomic orbital nature of the Be, Zr, and O atoms in BeZrO3. By estimating the Mulliken population charge, the bonding characteristics of BeZrO3 have been elucidated. Using the Born mechanical stability criterion, it was determined that BeZrO3 crystal is mechanically stable. The evaluation of ductile strength was expressed by using Poisson and Pugh’s critical ratios, revealing the inherent elastic anisotropy features. The optical characteristics have been conducted using various methodologies, concluded that BeZrO3 exhibits remarkable efficacy in absorbing ultraviolet and visible light.

Exploring the structural, mechanical, magneto-electronic and thermophysical properties of f electron based XNpO3 perovskites (X = Na, Cs, Ca, Ra).

Here, we present systematic investigation of the structural and mechanical stability, electronic profile and thermophysical properties of f-electron based XNPO3 (X = Na, Cs, Ca, Ra) perovskites by first principles calculations. The structural optimization, tolerance factor criteria depicts the cubic structural stability of these alloys. Further, the stability of these materials is also determined by the cohesive and formation energy calculations along with mechanical stability criteria. The electronic structure is explored by calculating band structure and density of states which reveal the well-known half-metallic nature of the materials. Further, we have calculated different thermodynamic parameters including specific heat capacity, thermal expansion, Gruneisen parameter and their variation with temperature and pressure. The thermoelectric effectiveness of these materials is predicted in terms of Seebeck coefficient, electrical conductivity and power factor. All-inclusive we can say that calculated properties of these half-metallic materials extend their route in spintronics, thermoelectric and radioisotope generators device applications.

A comparative ab-initio investigation of the physical properties of cubic Laves phase compounds XBi2 (X = K, rb)

In this study, we looked into a number of physical properties of alkali-bismuth compounds XBi2 (X = K, Rb), in the cubic Laves phase (symmetry Fd 3‾ m) using the density functional theory (DFT). The structural, elastic behavior along with Pugh's ratio, Poisson's ratio, Cauchy pressure, anisotropy indices, micro- and macro-hardness, thermo-physical properties such as Debye temperature, sound velocities, Grüneisen parameter, and melting temperature, electronic band structure, and optoelectronic properties has been explored. The computed ground-state lattice parameters and unit cell volume are in close accordance with the known theoretical and experimental findings. The elastic, thermo-physical, and optoelectronic properties of XBi2 (X = K, Rb) are investigated for the first time in this study. The computed elastic constants satisfied the mechanical stability criteria. The estimated Pugh's ratio, Poisson's ratio, and Cauchy pressure signify the ductility of the compounds. In order to understand the electronic properties, band structures and electronic energy densities of states have been explored. These compounds exhibit metallic characteristics in their electrical band structures. We have done a complete investigation on the reflectivity, absorption coefficient, refractive index, dielectric function, optical conductivity, and loss function of these metals. These compounds possess a low Debye temperature, thermal conductivity, and melting point. The optical absorption, reflectivity spectra and the refractive index of XBi2 (X = K, Rb) show that they can be used as solar reflector and ultraviolet absorber. The majority of the findings in this study are novel.

Mechanical and dynamical stability, electronic and bonding properties of a new narrow-gap semiconductor YPdAs Half-Heusler: DFT and QTAIM study

YPdAs is a semiconductor with an indirect band-gap of a value close to that of the direct one. Despite its important semiconductor behaviour, this half-Heusler compound has not yet been synthesized. Therefore, the main objective of this work is to confirm its energetic, mechanical and dynamical stability to prove that it can be formed experimentally and exploit it in optoelectronic applications. We have adopted two calculation methods to ensure accuracy of the results: FP-LAPW and PPs. Both methods gave negative formation energy values, which confirmed the energetic stability of YPdAs. Furthermore, YPdHCAs structure is the most stable. In this structure, the estimated elastic stiffness constants Cij perfectly satisfy the mechanical stability criteria. The analysis of phonon dispersion curve has shown a similarity between the two adopted methods (Direct method and DFPT). Given the absence of soft modes, the dynamical stability is confirmed for the first time. From the above, we confirm the possibility of synthesizing this compound experimentally. The electronic results show that the band-gap is indirect. There is no band inversion between VBM and CBM, which shows the trivial nature of this semiconductor. The detailed analysis of the bonds between the different atoms of this compound using QTAIM has shown the presence of only two bonds (Y–Pd and Pd–As) that have a similar character of a dative nature.

First-principles study on the structure and stability of (H<sub>2</sub>dabco)[K(ClO<sub>4</sub>)<sub>3</sub>] under hydrostatic pressure

The crystal structure, molecular structure, electronic structure and mechanical properties of molecular perovskite high-energetic material (H<sub>2</sub>dabco)[K(ClO<sub>4</sub>)<sub>3</sub>] (DAP-2) under hydrostatic pressure ranging from 0 to 50 GPa are calculated and studied based on density functional theory. And the influences of pressure on its stability and impact sensitivity of DAP-2 are investigated. As the external pressure gradually increases, both the lattice parameters and the volume of DAP-2 crystal exhibit a monotonic decreasing trend. In the entire pressure range, the unit cell volume shrinks by up to 40.20%. By using the Birch Munnaghan equation of state to fit <i>P</i>-<i>V</i> relation, the bulk modulus <i>B</i><sub>0</sub> and its first-order derivative <i>B</i><sub>0</sub>’ with respect to pressure are obtained to be 23.4 GPa and 4.9 GPa, respectively. The observations of the characteristic bond length and bond angle within the crystal indicate that the cage-like structure of organic cation H<sub>2</sub>dabco<sup>2+</sup> undergoes distortion at 25 GPa. Further analysis of the average fractional coordinates of the center-of-mass and Euler angles for H<sub>2</sub>dabco<sup>2+</sup> and KO<sub>12</sub> polyhedron shows that within a pressure range from 0 to 50 GPa, both the average fractional coordinates of the center-of-mass and the Euler angles exhibit fluctuations at 25 GPa, but the overall amplitude of these fluctuations is very small. Based on this finding, it is speculated that the space group symmetry of the crystal may remain unchanged in the entire pressure range. In terms of electronic structure, with the increase of pressure, the band gap value increases rapidly and reaches a maximum value at about 20 GPa, followed by a slow decreasing trend. Based on the first-principles band gap criterion and the variation of the band gap under different pressures, it is demonstrated that below 20 GPa, the impact sensitivity of DAP-2 gradually decreases with pressure increasing; however, when the pressure exceeds 20 GPa, the impact sensitivity exhibits a slow increasing trend. In addition, the elastic constants <i>C</i><sub><i>ij</i>,</sub> Young’s modulus (<i>E</i>), bulk modulus (<i>B</i>), shear modulus (<i>G</i>), and Cauchy pressure (<i>C</i><sub>12</sub> – <i>C</i><sub>44</sub>) all increase with pressure rising, indicating that the rigidity and ductility of the crystal under pressure are significantly strengthened. According to the mechanical stability criterion, the crystal maintains the mechanical stability throughout the pressure range.

First principles investigation of electronic and elastic properties of strontium oxide and strontium peroxide phases: insights into structural stability and phase transitions

Strontium oxide (SrO) and Strontium peroxide (SrO2) with multiple phases have been observed to exist at various temperatures and pressures, however there is little literature available on their properties. We have therefore attempted to discover several unexplored properties of various phases of SrO and SrO2. In this study, the electronic and elastic properties of SrO and SrO2 have been calculated via the first principle approach. We performed the said calculations over four available phases (FCC, BCC, hexagonal-1, and hexagonal-2) of SrO and two available phases (tetragonal and orthorhombic) of SrO2. The calculations have been conducted using density functional theory within the scalar-relativistic norm-conserving optimized Vanderbilt pseudopotential. In this study, equilibrium lattice parameter, elastic constants, structural stability, bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, Pugh ratio, Universal anisotropy index, Cauchy pressure and Kleinman’s internal strain parameter as elastic properties; the band gap and nature of the band gap as electronic properties have been calculated for the aforementioned materials. The phase transition between FCC-SrO and BCC-SrO has been observed during the calculation of elastic properties at 47 GPa. Based on the mechanical stability criteria, all phases except SrO(BCC) and SrO(Hexagonal-2) have been found to pass. The value of the bulk modulus have been observed between 68 GPa and 88 GPa for the different phases of SrOx [x = 1, 2]. Satisfactory agreement could be found between the present results and the available theoretical and experimental results.

Exploration energy harvesting through impurity-induced phenomena in barium titanate: First principle calculations

In this study, we used the plane-wave pseudopotential technique with PBE-GGA implemented in CASTEP code to investigate the structural, electronic, elastic, mechanical, optical, and thermal properties of Ca, Sr, and Ca/Sr(co-doping) doped barium titanate perovskite. Structural transformation from cubic to tetragonal was observed. Formation energy confirms thermodynamic stability. The tolerance factor verifies the adoption of perovskite crystal structure. Pristine and all doped compositions have suitable bandgap for solar cell applications. After doping in BaTiO3, more density of states are available; hence, charge mobility increases. Doping in BaTiO3 also induced an effect on its optical, elastic, mechanical and thermal properties. The refractive index, extinction coefficient, and energy loss function are reduced, which enhances the absorptive nature of the material. Thermal characteristics all show the suitability for energy harvesting applications. All doped compositions fulfil the mechanical stability criteria. Poisson and Pugh's ratio suggest that doping transforms material nature from brittle to ductile, which make it a suitable candidate for flexible solar cell and optoelectronic devices.

Mechanical stability criterions of cubic Na2He up to 500 GPa

The Cauchy pressure Cp was usually used to explain the atomic bonding character in a compound, while the mechanical stability criterions are usually used to study the stability of the structure under external compression. Using the elastic constants reported recently by Zahidur Rahaman et al. in Chinese Journal of Physics, 56 (2018) 231-237, as well as different mathematical formula, we reported on the Cauchy violation and the generalized mechanical stability criterions of cubic Na2He compound under high hydrostatic compression from 100 GPa to 500 GPa. For pressures ranging from 100 to 500 GPa, all values of both Cauchy pressure Cp and the generalized mechanical stability criteria G are negative. In addition we calculated the Debye temperature θD of Na2He compound using Siethoff’s approach. The results obtained are slightly lower than those obtained from the Debye approach reported by Zahidur Rahaman et al.

A DFT study of the structural, magnetic, electronic, mechanical and optical properties of M0.75Cu0.25Fe2O4 (M = Co, Ni, Mg, Mn) ferrites: Optoelectronic applications

DFT calculations were used to investigate the structural, magnetic, electronic, mechanical and optical properties of M0.75Cu0.25Fe2O4 (M = Co, Ni, Mg, Mn) ferrites by employing the CASTEP Code. The simulated XRD of M0.75Cu0.25Fe2O4 (M = Co, Ni, Mg, Mn) ferrites revealed an increase in lattice constants (8.353–8.501 Å), d-spacings (2.426–2.592 Å), the volume of the unit cell (582.811–614.342 Å3), hopping lengths (LA = 7.234–7.441 Å; LB = 5.906–6.074 Å) and a decrease in X-ray density (5.376–5.035 g/cm3). The M0.75Cu0.25Fe2O4 (M = Co, Ni, Mg, Mn) ferrites exhibited the characteristics of direct bandgap semiconductor materials, which increased from 0.931–1.176 eV The computed DOS revealed that M0.75Cu0.25Fe2O4 (M = Co, Ni, Mg, Mn) ferrites exhibited good spin polarization behavior as well, and according to Hirshfeld analyses, the magnetic moment from 3.348–1.436 μB and saturation magnetization from 79.264–34.435 emu/g were increased. The cubic crystal mechanical stability criteria of M0.75Cu0.25Fe2O4 (M = Co, Ni, Mg, Mn) ferrites indicated that all ferrites were mechanically stable as potential candidates in electrochemical applications. The values of Pugh's ratio of M0.75Cu0.25Fe2O4 (M = Co, Ni, Mg, Mn) ferrites predicted the ductile nature of all ferrites and all the values of Poisson's ratio exhibited the behavior of ionic bonds of all ferrites. The optical characteristics of M0.75Cu0.25Fe2O4 (M = Co, Ni, Mg, Mn) ferrites lie in visible regions, which proved suitable candidates in optoelectronic applications.

Mechanical properties, tensile strength, anisotropy and electronic properties of ZrxSiy intermetallics

The thermodynamic properties, mechanical, ideal tensile strength, fracture toughness, anisotropy and electronic properties of Zr2Si, Zr3Si2, ZrSi2, Zr5Si3 α-ZrSi and β-ZrSi are studied by using the first principles. The results indicate that the six Zr-Si compounds satisfied with the structural stability. The elastic constants indicate that the six compounds satisfied with the mechanical stability criteria. The values of the ideal tensile strength were calculated for Zr-Si intermetallics. It is worth noting that β-ZrSi has the highest values of three elastic moduli among the six Zr-Si intermetallics, while ZrSi2 has the lowest values for three moduli. The Poisson's ratio indicates that six intermetallics are all brittle. The order of hardness is: Zr2Si > β-ZrSi > Zr5Si3 > ZrSi2 > Zr3Si2 > α-ZrSi. The fracture toughness of Zr5Si3 is the largest and ZrSi2 is the smallest. α- ZrSi has the best damage tolerance. The elastic anisotropy index, surface structures and projections indicate that six intermetallics are elastic anisotropy. Meanwhile, the elastic anisotropy is further explained by the sound velocity along the different directions. Debye temperature further confirmed the reason why ZrSi2 has the maximum hardness. Moreover, the electronic structures explain the mechanical properties.

First principle insights into the physical properties of Ti-based 211-MAX phase nitrides Ti2AN (A = Tl and Pb)

We have used the theoretical ab initio approach to scrutinize the electronic and other physical properties of Ti2AN (A = Tl and Pb). Geometrical optimization has been carried out to obtain accurate lattice constants and internal coordinates. The formation energies of Ti2TlN and Ti2PbN are found to be negative, which confirms their stability. The aforementioned compounds are found to be metallic because of their zero-band gaps. The metallicity f m (x 10−3) of Ti2TlN and Ti2PbN phases were determined to be 1.77 and 2.11, respectively. In addition, we evaluate the elastic constant C ij , which obeys the Born-Huang mechanical stability criterion. We used the Voigt-Reuss-Hill approximation for the analysis of Young’s modulus, shear modulus, and bulk modulus successfully. Furthermore, Ti2TlN is found to be brittle, but Ti2PbN is close to the brittle-ductile boundary line according to Pugh’s and Poisson’s ratios. The Debye temperature, melting temperature, and minimum thermal conductivity have all been rigorously studied to examine the potential scenarios of genuine high-temperature applications. Lower Young’s modulus, the minimum thermal conductivity (Ti2TlN and Ti2PbN), and Debye temperature values reveal that Ti2PbN might be used as a thermal barrier coating application. A study of elastic anisotropy demonstrates that Ti2PbN has a higher degree of anisotropy than Ti2TlN, according to the universal anisotropy index. We confirmed the dynamic stability (i.e., no negative frequencies at the gamma point) of predicted compounds by performing phonon DOS and phonon band structures. Finally, the temperature-dependent thermodynamic properties of Ti2TlN and Ti2PbN have been thoroughly analyzed, where the entropy (S), free energy, and internal energy (E) vary with respect to temperature. Moreover, the convergence of specific heat capacity is observed at constant volume to the Dulong-Petit limit at higher temperatures.