Universal Anisotropy Index Research Articles

Ab Initio Studies of Mechanical, Dynamical, and Thermodynamic Properties of Fe-Pt Alloys.

The density functional theory (DFT) framework in the generalized gradient approximation (GGA) was employed to study the mechanical, dynamical, and thermodynamic properties of the ordered bimetallic Fe-Pt alloys with stoichiometric structures Fe3Pt, FePt, and FePt3. These alloys exhibit remarkable magnetic properties, high coercivity, excellent chemical stability, high magnetization, and corrosion resistance, making them potential candidates for application in high-density magnetic storage devices, magnetic recording media, and spintronic devices. The calculations of elastic constants showed that all the considered Fe-Pt alloys satisfy the Born necessary conditions for mechanical stability. Calculations on macroscopic elastic moduli showed that Fe-Pt alloys are ductile and characterized by greater resistance to deformation and volume change under external shearing forces. Furthermore, Fe-Pt alloys exhibit significant anisotropy due to variations in elastic constants and deviation of the universal anisotropy index value from zero. The equiatomic FePt showed dynamical stability, while the others showed softening of soft modes along high symmetry lines in the Brillouin zone. Moreover, from the phonon densities of states, we observed that Fe atomic vibrations are dominant at higher frequencies in Fe-rich compositions, while Pt vibrations are prevalent in Pt-rich.

Enhancing mechanical properties of MgB2 superconductors through Nb substitution: A first-principles study

MgB2 has a wide range of applications as a crucial superconducting material in fields such as electronics and communications, but its weak mechanical properties limit its use in extreme environments such as high pressure. Therefore, this article explores the enhancement mechanism of the mechanical properties for MgB2 by substituting Mg sites with Nb element based on first principles. After substitution, NbB2 has better thermodynamic stability, and the introduction of Nb-d state enhances light absorption. In terms of mechanics, due to the higher electron accumulation density in the Nb–B bond and a shorter bond length (2.451 Å), the atomic interactions become tighter and stronger. As a result, both elastic constants and modulus are enhanced, exhibiting high stiffness, high compression resistance, etc. The spatial distribution of 3D elastic anisotropy is closer to a spherical shape and the universal anisotropy index (AU) tends to approach 0, which indicates the mechanical properties in all directions are more consistent, making it easier to predict and control. Meanwhile, the elastic modulus rises smoothly with increasing hydrostatic pressure and is not affected by lattice compression at low hydrostatic pressure. The change rate of B–B bond length is 6.8 % at 100 GPa, which becomes the main reason for the enhancement of mechanical properties. The article provides a theoretical foundation for the preparation of superconductors with excellent mechanical properties under extreme conditions.

Multi-scale investigation of the mechanical-structural hallmarks of cubic-silicon-carbide under elevated pressures: Hirshfeld topological surfaces-first principles synergic approach

The pressure-induced evolution of cubic-silicon-carbide (3 C-SiC) crystal structure, elastic constants, and bond lengths are systematically elucidated, shedding light on its behavior across a wide range of thermodynamic states. The study employs a Hirshfeld topological surfaces-first principles synergic approach to comprehensively analyze the structure and thermal, and elastic hallmarks of 3 C-SiC single crystal under elevated pressure. The study reveals intricate details regarding the pressure-density relationship, providing valuable perceptions into the single crystal response to external stimuli. In particular, the elastic properties, including Young's- (320<Y<339 GPa), shear-modulus (179<S<195 GPa), and Poisson's-ratio (0.248<σ<0.370), are explored in depth as a function of applied stress, offering a inclusive insights of the material's response to external stimuli. The analysis also explored the Hirshfeld surfaces including the globularity and asphericity of both the unit cell and individual SiC molecules. The universal anisotropy index, a crucial parameter for understanding material anisotropy, is also computed. The increasing globularity, particularly at the molecular level, may enhance force distribution in the crystal lattice, potentially affecting both bond lengths and elasticity and promoting isotropic behavior. The constant unit cell asphericity indicates a resilient structural response to pressure variations, suggesting stability in bond lengths and potential influence on the elastic behavior of 3 C-SiC crystal. The study focuses on advanced materials and computational methods, providing helpful inspirations into the performance of 3 C-SiC under elevated pressure relevant to various technological domains.

Elasticity of dense anisotropic carbons: A machine learning model of the structure–property relationship informed by large scale molecular dynamics data

Dense anisotropic carbons are praised materials for thermostructural applications, yet, so far, a detailed structure–property relationship for these materials is still lacking, especially for the pyrocarbon (pyC) matrices in carbon/carbon composites. Here we compute the full elastic tensors of 210 recently introduced nanoscale models of anisotropic carbons (Polewczyk et al., 2023), covering domain sizes (Lc and La) and orientation angles (OA, as a measure of nanotexture) relevant to most as-prepared and moderately heat-treated pyC matrices: Lc∈ [1.5:8 nm]; La∈ [2:5.5 nm]; and OA ∈ [25:110°]. Isothermal and adiabatic elastic tensors, corresponding to the slow quasi-static and ultra-fast loading regimes, respectively, are considered. Analyzing the database of computed elastic constants with a random forest regressor supervised learning algorithm we show that all elastic constants can be predicted accurately using Lc, La and OA as descriptors. Among the latter, OA is the one showing, by far, the strongest correlation with the elastic tensors. For such dense, non porous carbons, 3 of the 6 isothermal and 5 of the 6 adiabatic constants can even be accurately predicted using OA as the unique material descriptor. Calculation of the universal anisotropy index shows that isothermal tensors show more anisotropy than adiabatic ones, indicating that stress relaxation favors elastic anisotropy. Eventually, the Young’s moduli and Poisson coefficients of six models of actual pyCs are presented and their longitudinal moduli compared to tensile measurements, showing relatively poor agreement. These results suggest that accounting for texture at a larger scale is required to capture pyC matrices elasticity. The developed supervised learning model is available for online use at https://web.ism.u-bordeaux.fr/rfr.

First-principles calculations to investigate structural, elastic and electronic properties of chloro-perovskite NaMgCl3

In this work, we have investigated the structural, electronic, and optical properties of the halide-perovskite NaMgCl3 by performing first-principles calculations using a mixed basis of the full-potential linearized augmented plane wave (FP-LAPW) approach under the generalized gradient approximation (GGA-PBEsol), a revised Perdew-Burke-Ernzerhof, and the modified Becke-Johnson (TB-mBJ) implemented on the Wien2k package. The obtained results show that NaMgCl3 is more stable in the nonmagnetic phase.The compound is found to be thermodynamically and elastically stable. It is found that there is a good agreement between the calculated lattice constants and the values published in previous studies. The complete set of first-order elastic constants tensor has been calculated, implying mechanical stability. The Young's modulus, shear modulus, Poisson's ratio,Pugh's ratio, and universal anisotropy index have been additionally calculated. The atomic bonds along both x and y axis are stronger than those along the z-axis. The Debye temperature is calculated using the average sound velocity. From electronic band structures, we have found that NaMgCl3 is an insulator with a direct wide band gap ΓV→ΓC. The electronic charge densities were plotted.Analysis of the charge density distribution map reveals that the bondings in NaMgCl3 are ionic. The calculated density of states (DOS) indicates that the valence band is mainly dominated by Cl− anions, the conduction band is mainly dominated by Mg2+ cations, whereas Na+ has a negligible contribution. The optical characteristics, notably the dielectric function tensor, refractive function, reflectivity, absorption coefficient, photo-conductivity and transmittance were plotted and discussed. The optical properties confirm that NaMgCl3 is optically anisotropic in 10–24 eV range .The low transmittance and high absorption coefficient in the far ultra-violet region, between 90 and 250 nm, make this compound a good candidate for use as an ultraviolet shield, in vacuum ultraviolet lenses and in thermoelectric promising features due to his direct wide band gap.Experimental and theoretical data are scarce for this compound in an ilmenite-type structure.

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.

A comparative ab initio study on mechanical and thermal properties of rare-earth scandate LnScO3 (Ln = La, Pr, Nd, Sm, Eu and Tb) compounds

To comparatively examine the mechanical and thermal properties of rare-earth scandate LnScO3 (Ln = La, Pr, Nd, Sm, Eu and Tb) compounds, ab initio calculation based on density functional theory was used within the framework of the generalized gradient approximation. The elastic moduli, Pugh’s criterion, Poisson’s ratio, Vickers hardness, linear compressibility, Debye temperature, Grüneisen parameter, elastic wave velocities, minimum thermal conductivities of LnScO3 were successfully obtained from independent single crystal elastic coefficients. The computed elastic constants indicate that these compounds have mechanical stability. The ductile and brittle properties of LnScO3 compounds were investigated using the B H /G H , Poisson’s ratio and Cauchy pressure. The mechanical anisotropic properties of LnScO3 compounds were discussed using universal anisotropic index, shear anisotropy factors, percentage shear (compressible) anisotropy index. Minimum thermal conductivities of LnScO3 were determined using Cahill’s and Clark’s model. Except for the elastic coefficients of NdScO3, SmScO3 and TbScO3 compounds, many physical properties of LnScO3 compounds were calculated for the first time in this study. We compared our calculation results with experimental and other theoretical data available in the literature.

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.

First-Principle Investigation into Mechanical Properties of Al6Mg1Zr1 under Uniaxial Tension Strain on the Basis of Density Functional Theory

The influences of uniaxial tension strain in the x direction (εx) on the mechanical stability, stress–strain relations, elastic properties, hardness, ductility, and elastic anisotropy of Al6Mg1Zr1 compound were studied by performing first-principle calculations on the basis of density functional theory. It was found that Al6Mg1Zr1 compound is mechanically stable in the range of strain εx from 0 to 6%. As the strain εx increased from 0 to 6%, the stress in the x direction (σx) first grew linearly and then followed a nonlinear trend, while the stresses in the y and z directions (σy and σz) showed a linearly, increasing trend all the way. The bulk modulus B, shear modulus G, and Young’s modulus E all dropped as the strain εx increased from 0 to 6%. The Poisson ratio μ of Al6Mg1Zr1 compound was nearly unchanged when the strain εx was less than 3%, but then it grew quickly. Vickers hardness HV of Al6Mg1Zr1 compound dropped gradually as the strain εx increased from 0 to 6%. The Al6Mg1Zr1 compound was brittle when the εx was less than 4%, but it presented ductility when the strain εx was more than 4%. As the strain εx increased from 0 to 6%, the compression anisotropy percentage (AB) grew and its slope became larger when the strain εx was more than 4%, while both the shear anisotropy percentage (AG) and the universal anisotropy index (AU) first dropped slowly and then grew quickly. These results demonstrate that imposing appropriate uniaxial tension strain can affect and regulate the mechanical properties of Al6Mg1Zr1 compound.

Structural, Electronic, Elastic, Mechanical, and Opto-Electronic Properties for ZnAg2SnS4 and ZnAg2Sn0.93Fe0.07S4 Photocatalyst Effort on Wastewater Treatment through the First Principle Study

The stannite structured ZnAg2SnS4 was developed from its parent composition ZnAg2GeS4, which is considered to be an excellent photocatalytic material, as the demands for photocatalytic effect on organic and waste water treatment have been increasing around the globe. First and foremost, the geometry optimization was performed by density functional theory (DFT) of the generalized gradient approximation (GGA) with Perdew–Burke–Ernzerhof (PBE)-ballpark figured as the successful candidate for computational screening containing heavy metal complexes. The structural geometry parameters were determined along with the electronic band structure, density of state (DOS), partial density of state (PDOS), Mulliken charge population, elastic constant, and optical characteristics. When the Ge (ZnAg2GeS4) atom has been swapped out by a Sn (ZnAg2SnS4) atom, the changes in band gap is noticeable, which rises from 0.94 eV to 1.15 eV with the same geometry and surface area. But, after 7% Fe doping, it has decreased to 0.32 eV. The PDOS demonstrates that the production of hydrogen for photocatalytic influence on wastewater treatment is dependent on the Fe atom's ability to induce and boost the electron density in both the conduction band and the valence band. The study of the elastic constant and mechanical constant revealed that these crystals are extremely stable in any environment. The dielectric constant and optical absorptions illustrate the superior evidence for photocatalytic activity. To sum up, it could be said that after doping of Fe, the elastic constant and mechanical constant show all universal anisotropic index crystals and ZnAg2Sn0.93Fe0.07S4 can absorb a variety of UV radiation, which raises the possibility that it could function as a photocatalyst.

Elastic, anisotropic, lattice dynamics and electronic properties of XNiM and XNi2M (X = Ti, Zr, Hf; M = Sn, Ge, Si): DFT comparison study

The ab-initio calculations were performed using density functional theory (DFT) as implemented in the Quantum ESPRESSO (QE) code. Lattice parameter mismatch was minimal (2.5 % - 3 %) in TiNiSn/TiNi2Sn, ZrNiSn/ZrNi2Sn, and HfNiSn/HfNi2Sn compounds. Half-Heusler compounds had shorter bond lengths and smaller bulk moduli than their full-Heusler counterparts. Directional dependencies of the Young’s and shear moduli were investigated using elastic constants. TiNiGe, HfNiSn, and ZrNiSn had a greater universal anisotropy index among the half-Heusler compounds. Half-Heusler, TiNi2Sn, TiNi2Si, ZrNi2Sn, and HfNi2Sn compounds are reported to be dynamically stable. The electronic structure computations show that TiNiSn, ZrNiSn, and HfNiSn compounds have the least indirect energy gaps of 0.4508 eV, 0.5019 eV, and 0.3847 eV respectively. TiNiSn, ZrNiSn, and HfNiSn compounds are good candidates for minimizing the thermal conductivity of thermoelectric devices. TiNi2Sn, ZrNi2Sn, and HfNi2Sn are good candidates as possible contact electrodes for TiNiSn, ZrNiSn, and HfNiSn.

First principles study of the structural, mechanical and optical properties of Li6PS5X (X= Cl, I) argyrodite compounds

Phosphorus-containing argyrodite are now gaining high attention for energy storage devices. Here, the electronic, structural, optical and elastic properties of Li6PS5X (X = Cl, I) argyrodites by utilizing density functional theory (DFT) have been studied. Trans-Blaha approach of the modified Becke–Johnson (TB-mBJ) potential is used to get accurate band gap energy values where the (PBEsol-GGA) are used for the calculations of the structural parameters of Li6PS5Cl and Li6PS5I compounds with lattice parameters of 10.31 Å and 10.36 Å respectively. The mBJ-functional shows energy bandgap of Li6PS5Cl to be 3.11 eV and for Li6PS5I with band gap of 2.81 eV. The static refractive index for Li6PS5Cl and Li6PS5I are 2.23 and 1.90. Elastic constants of the cubic compounds C11, C12 and C44 and different moduli like Young modulus, Shear moduli alongwith different parameters like Kleinman's parameters, first and second Lame constants, Hardness, Melting temperature, Chung-Buessem anisotropy index, universal anisotropic index, acoustic behavior and its anisotropy, Poisson ratios. Mechanically the compounds determined as brittle. The current study has reported many new results on the argyrodite compounds which maybe interesting for future experimental studies and further theoretical exploration of the family of these compounds.

Theoretical Prediction of Structural, Mechanical, and Thermophysical Properties of the Precipitates in 2xxx Series Aluminum Alloy

We presented a theoretical study for the structural, mechanical, and thermophysical properties of the precipitates in 2xxx series aluminum alloy by applying the widely used density functional theory of Perdew-Burke-Ernzerhof (PBE). The results indicated that the most thermodynamically stable structure refers to the Al3Zr phase in regardless of its different polymorphs, while the formation enthalpy of Al5Cu2Mg8Si6 is only -0.02 eV (close to zero) indicating its metastable nature. The universal anisotropy index of AU follows the trend of: Al2Cu &gt; Al2CuMg ≈ Al3Zr_D022 ≈ Al20Cu2Mn3 &gt; Al3Fe ≈ Al6Mn &gt; Al3Zr_D023 ≈ Al3Zr_L12 &gt; Al7Cu2Fe &gt; Al3Fe2Si. The thermal expansion coefficients (TECs) were calculated based on Quasi harmonic approximation (QHA); Al2CuMg shows the highest linear thermal expansion coefficient (LTEC), followed by Al3Fe, Al2Cu, Al3Zr_L12 and others, while Al3Zr_D022 is the lowest one. The calculated data of three Al3Zr polymorphs follow the order of L12 &gt; D023 &gt; D022, all of them show much lower LTEC than Al substance. For multi-phase aluminum alloys, when the expansion coefficient of the precipitates is quite different from the matrix, it may cause a relatively large internal stress, or even produce cracks under actual service conditions. Therefore, it is necessary to discuss the heat misfit degree during the material design. The discrepancy between a-Al and Al2CuMg is the smallest, which may decrease the heat misfit degree between them and improve the thermal shock resistant behaviors.

Dynamical, mechanical, anisotropic, and thermodynamic properties of Mg-XL-Y (XL = Zn, Al) alloys with long-period stacking ordered structures: A first-principles calculation

The dynamical, mechanical, anisotropic, and thermodynamic properties of Mg-XL-Y (XL = Zn, Al) alloys based on three long-period stacking ordered (LPSO) phases (ie, 10H, 14H, and 18R) have been investigated systematically by first-principles calculations. The LPSO phases of Mg-XL-Y (XL = Zn, Al) alloys are thermodynamically, dynamically, and mechanically stable. The each LPSO phase of Mg–Al–Y alloys has superior mechanical properties with larger resistances to deformation under applied stress and shear pressure, stiffness, as well as hardness than those of corresponding to LPSO phases of Mg–Zn–Y alloys. According to universal elastic anisotropic index, percent shear anisotropy, 3D surface structures of Young's moulus, and sound velocities, the LPSO phases of Mg-XL-Y (XL = Zn, Al) alloys exhibit obvious anisotropy. Besides, all LPSO phases of Mg-XL-Y (XL = Zn, Al) alloys possess low lattice thermal conductivity due to the strong anharmonicity. The calculated adsorption energies indicate that the 14H(001) surface of Mg–Al–Y system at the hollow site is more sensitive to absorb O atom.

An efficient analytical method to obtain the homogenised frequency-independent elastic material properties of cross-laminated timber elements

Cross-Laminated Timber (CLT) is a renewable, sustainable, and cost-efficient building element that has been growing in popularity in recent years. To improve one of CLT’s weaknesses, its suboptimal noise and vibration isolation performance, computationally efficient, accessible, and extensible CLT vibro-acoustic models are required. An effective approach to achieve such models is the homogenisation of layered materials. This paper presents a validated homogenisation method based on First-order Shear Deformation Theory (FSDT) that obtains the frequency-independent elastic material properties of CLT. This method is applicable to arbitrary linear elastic material properties, orientations, and stacking sequences of the layers. The homogenised material properties are utilised with FSDT Equivalent Single-Layer (ESL) models that are readily implemented with many finite element method codes to calculate the vibro-acoustic behaviour of CLT elements, even including thickness resonance effects when applied with an appropriate model. The presented homogenisation method for CLT is validated in a numerical study by comparing the mechanical mobilities of ESL models against layerwise dynamic models. The numerical study is conducted based on an experimentally validated 5-ply model for 2- to 7-ply CLT plates with proportionally increasing thicknesses and three idealised boundary conditions. The frequency-independent material properties also allow for the graphical exploration of the anisotropic nature of CLT and the calculation of the universal anisotropic index. The flexibility of the homogenisation method, combined with its ready implementation in already widely implemented FSDT models, can have an application and impact beyond the vibro-acoustic considerations of CLT into the general mechanical modelling of CLT as it is implemented in ever more advanced applications.

Design of elastically isotropic shell lattices from anisotropic constitutive materials for additive manufacturing

Additively manufactured elastically isotropic lattice structures are promising for lightweight structural applications. Current design methods for elastically isotropic lattice structures are mostly based on the assumption of isotropic constitutive materials. However, additive manufacturing (AM) fabricated materials generally exhibit undesired anisotropy due to the layer-by-layer construction, which requires precise material models to be incorporated in structural design framework. This work presents a design method of variable thickness triply periodic minimal surface (TPMS) shell lattices to achieve elastic isotropy from homogeneous anisotropic constitutive materials. A gradient-based optimization method which adopts the universal anisotropy index as the objective is developed to handle any orthotropic lattices, extending the widely used method based on the Zener anisotropy ratio that only suits cubic lattices. To validate the proposed design method, the transversely isotropic elasticity model of micro laser powder bed fusion (μLPBF) fabricated stainless steel 316 L (SS316L) is calibrated through tensile tests, and then incorporated into the optimization method to design elastically isotropic variable thickness N14, IWP, and P shell lattices. Compression tests results of μLPBF fabricated N14 lattices demonstrate that the proposed design reduces the relative standard deviation of the lattice’s Young’s moduli along nine directions from 0.77 (uniform thickness) to 0.75. Further numerical analysis reveals that the Young’s moduli of N14, IWP and P shell lattices along [001] direction are reduced by 2%−6% depending on the lattice type, while those along [100] and [101] directions remain almost constant after anisotropic SS316L ( E z / E x = 0.92) replaces the isotropic one. This work provides a design and analysis method for AM fabricated TPMS shell lattices made of anisotropic constitutive materials, and reveals the influences of anisotropic constitutive materials on the elastic properties of lattices.

Structural stabilities, mechanical and thermodynamic properties of chalcogenide perovskite ABS3 (A = Li, Na, K, Rb, Cs; B = Si, Ge, Sn) from first-principles study

In this study, first-principles calculations have been used to study the mechanical and thermodynamic properties of chalcogenide perovskite ABS3 (A = Li, Na, K, Rb, Cs; B = Si, Ge, Sn) in the triclinic phase. The structural stabilities of perovskite were investigated through Goldschmidt’s tolerance factor (t) and phonon dispersion. It was indicated that all of the investigated materials construct stable perovskite structures. The mechanical properties of chalcogenide perovskites ABS3 were systematically investigated by density functional theory (DFT). The DFT method was considered within the meta-generalized gradient approximation revTPSS. The elastic properties of materials give the data necessary in understanding the bonding property between adjacent atomic planes, stiffness, bonding anisotropic, and structural stability of the material. The independent elastic constants Cij have been used for the prediction of mechanical properties like bulk modulus (B), Shear modulus (G), Young’s modulus (E) Poisson’s ratio (ν), and the universal anisotropic index (AU). The mechanical stability, brittleness, and ductility behaviors of materials were discussed. The covalent, ionic, and metallic nature of the materials were also discussed. The thermodynamic parameters including heat capacity, entropy, enthalpy, and free energy were also computed and discussed with a wide range of temperatures (0–1000 K).

STRUCTURAL AND ELASTIC PROPERTIES OF AgNi10 ALLOY STUDIED WITH AB-INITIO CALCULATIONS

First-principles calculations based on density functional theory (DFT) are used to calculate the structural, elastic and thermodynamic properties of the supersaturated solid-solution AgNi10 alloy, applied mainly to electrical contact materials. In this work, for the exchange-correlation energy, the generalized gradient approximation (GGA) functional is used. The calculated structural and electronic properties of supersaturated solid-solution AgNi10 alloys show that the occupation of Ni in the Ag lattice is ordered. All single-crystal elastic stiffness constants of the energetically and mechanically optimized stable AgNi10 model are calculated using the finite strain method and using the Voigt-Reuss-Hill approximation. Various anisotropic indices like the universal anisotropic index, shear anisotropic index, directional dependence of Young’s modulus, bulk modulus and others are calculated to study the elastic anisotropy. The strong anisotropy in the elastic properties of AgNi10 was confirmed. Phonon dispersions were carried out, showing that the AgNi10 crystal has dynamic stability. The Debye temperature is calculated from the elastic data by estimating the average sound velocity in the AgNi10. Furthermore, the vibrational thermodynamic properties (free energy, enthalpy, entropy and heat capacity) of AgNi10 are obtained successfully.

Corrosion Protection Oxide Scale Formed on Surface of Fe-Ni-M (M = Al, Cr, Cu) Inert Anode for Molten Salt Electrolysis.

An oxide scale formed on the surface of metal anodes is crucial for determining the overall quality of molten salt electrolysis (MSE), particularly for the durability of the anode materials. However, the material properties of oxide scales are yet to be revealed, particularly in ternary spinel oxide phases. Therefore, we investigate the mechanical and thermal properties of spinel oxides via first-principles calculations. The oxides are calculated using the models of normal (cubic) and inverse (orthorhombic) spinel compounds. The d-orbital exchange correlation potential of transition metal oxides is addressed using the generalized gradient approximation plus Hubbard U. The lattice constant, formation energy, cohesive energy, elastic modulus, Poisson’s ratio, universal anisotropy index, hardness, minimal thermal conductivity, and thermal expansion coefficient are calculated. Based on the calculated mechanical and thermal properties of the spinel compound, the Fe–Ni–Al inert anode is expected to be the most suitable oxide scale for MSE applications among the materials investigated in our study.

Tailoring the mechanical response of Ruddlesden Popper lead halide perovskites

Two dimensional (2D) Ruddlesden Popper perovskites have been extensively studied for their exceptional optical and electronic characteristics while only a few studies have shed light on their mechanical properties. The existing literature mainly discusses the mechanical strength of single crystal perovskites, however a study of structure tunability of 2D perovskite thin films is still missing. In this study, we report the effect of number of inorganic layers ‘n’ on elastic modulus of 2D, quasi-2D perovskites and 3D perovskite thin films using nanoindentation technique. Our studies indicate the role of orientation of the inorganic layers in perovskite films in tailoring their mechanical response. The experimental results have been substantiated using first principle density functional theory (DFT) calculations. We also report other important mechanical parameters namely, shear modulus, bulk modulus, Poisson’s ratio, Pugh’s ratio, Vickers hardness, yield strength and the universal elastic anisotropic index using DFT simulations. Anisotropy is observed in the elastic modulus of the materials under study and has been discussed in detail in the manuscript. Understanding the mechanical behavior of 2D Ruddlesden Popper perovskites thin film in comparison with conventional 3D perovskite offers intriguing insights into the atomic layer dependent properties and paves the path for next generation mechanically durable and novel devices.