Strukturna, elastična, elektronska i rešetkina svojstva legura GaPxAsySb1−x−y S rešetkama priležnim dvjema podlogama

Information on the energy band gaps, the lattice parameter and the lattice matching to available substrates is a prerequisite for many practical applications. A pseudopotential plane-wave method, as implemented in the ABINIT code, is used to the GaPxAsySb1−x−y quaternary alloy lattice matched to GaAs and InP substrates to predict their energy band gaps, elastic constants and lattice dynamic properties. The ranges of compositions for which the alloy is lattice-matched to GaAs and InP are determined. A very good agreement is obtained between the calculated values and the available experimental data of GaAs and GaAs0.5Sb0.5 parents. The compositional dependence of direct and indirect band gaps has been investigated. Note that a phase transition occurred at As composition of 0.018 and 0.576 for GaPxAsySb1−x−y within InP and GaAs substrates. The static and high-frequency dielectric constants and refractive index are indeed inversely proportional (proportional) to the fundamental band gap for GaPxAsySb1−x−y within InP (GaAs) substrates. We study the variation of elastic constants, the optical phonon frequencies (ωTO and ωLO) and the Born effective charge Z* with As concentration.Podaci o energijskim procijepima, parametrima rešetke i prileživanju na dostupne podloge je preduvjet mnogin primjenama. Rabimo metodu ravnih valova s pseudopotencijalom, primijenjenu u programu ABINIT, da bismo predvidjeli procijepe energijskih vrpci, elastične konstante i dinamička svojstva rešetaka legure GaPxAsySb1−x−y s četiri sastavnice, priležne na GaAs i InP podloge. Odredili smo područja sastava za koja rešetke priliježu na GaAs i InP. Postigli smo vrlo dobar sklad izračunatih vrijednosti s eksperimentalnim podacima za polazne legure GaAs i GaAs0.5Sb0.5. Istražili smo ovisnost izravnih i neizravnih procijepa vrpci o sastavu. Opaža se pojava faznog prijelaza za sadržaj As od 0.018 i 0.576 u GaPxAsySb1−x−y na InP i GaAs podlogama. Statičke i visokofrekventne dielektrične konstante te indeks loma su obrnuto razmjerni (razmjerni) širini osnovnog procijepa vrpci u GaPxAsySb1−x−y na InP and GaAs podlogama. Proučavamo promjene elastičnih konstanti, optičkih fononskih frekvencija (ωTO i ωLO) te Bornovog efektivnog naboja Z ∗ u ovisnosti o sadržaju As

Strukturna, elastična, elektronska i rešetkina svojstva legura GaPxAsySb1−x−y S rešetkama priležnim dvjema podlogama

Information on the energy band gaps, the lattice parameter and the lattice matching to available substrates is a prerequisite for many practical applications. A pseudopotential plane-wave method, as implemented in the ABINIT code, is used to the GaPxAsySb1−x−y quaternary alloy lattice matched to GaAs and InP substrates to predict their energy band gaps, elastic constants and lattice dynamic properties. The ranges of compositions for which the alloy is lattice-matched to GaAs and InP are determined. A very good agreement is obtained between the calculated values and the available experimental data of GaAs and GaAs0.5Sb0.5 parents. The compositional dependence of direct and indirect band gaps has been investigated. Note that a phase transition occurred at As composition of 0.018 and 0.576 for GaPxAsySb1−x−y within InP and GaAs substrates. The static and high-frequency dielectric constants and refractive index are indeed inversely proportional (proportional) to the fundamental band gap for GaPxAsySb1−x−y within InP (GaAs) substrates. We study the variation of elastic constants, the optical phonon frequencies (ωTO and ωLO) and the Born effective charge Z* with As concentration.Podaci o energijskim procijepima, parametrima rešetke i prileživanju na dostupne podloge je preduvjet mnogin primjenama. Rabimo metodu ravnih valova s pseudopotencijalom, primijenjenu u programu ABINIT, da bismo predvidjeli procijepe energijskih vrpci, elastične konstante i dinamička svojstva rešetaka legure GaPxAsySb1−x−y s četiri sastavnice, priležne na GaAs i InP podloge. Odredili smo područja sastava za koja rešetke priliježu na GaAs i InP. Postigli smo vrlo dobar sklad izračunatih vrijednosti s eksperimentalnim podacima za polazne legure GaAs i GaAs0.5Sb0.5. Istražili smo ovisnost izravnih i neizravnih procijepa vrpci o sastavu. Opaža se pojava faznog prijelaza za sadržaj As od 0.018 i 0.576 u GaPxAsySb1−x−y na InP i GaAs podlogama. Statičke i visokofrekventne dielektrične konstante te indeks loma su obrnuto razmjerni (razmjerni) širini osnovnog procijepa vrpci u GaPxAsySb1−x−y na InP and GaAs podlogama. Proučavamo promjene elastičnih konstanti, optičkih fononskih frekvencija (ωTO i ωLO) te Bornovog efektivnog naboja Z ∗ u ovisnosti o sadržaju As

Effect of Mg contents on the mechanical proprieties and precipitation kinetics in Al–3.3 wt.% Cu alloy

The effect of additional Mg on the microstructure, mechanical properties, and transformation kinetics during aging in Al–3.3 wt.% Cu alloy was studied. The compositions and microstructure were examined by X-ray diffraction, Differential scanning calorimetry (DSC) and scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy (EDS). The results show that the Mg in the Al–Cu alloy mainly precipitated to the grain boundaries during the process of transformation and formed a ternary Al2CuMg metallic compound and the rate of discontinuous precipitation reaction decreases with increasing concentration of Mg. The activation energy of crystallization was evaluated by applying the Kissinger equation

Роль магистратуры в процессе гармонизации европейского пространства высшего образования

In this paper, we report the by first-principles predicted properties of the recently discovered magnetic MAX phase Mn2GaC. The electronic band structure and vibrational dispersion relation, as well as the electronic and vibrational density of states, have been calculated. The band structure close to the Fermi level indicates anisotropy with respect to electrical conductivity, while the distribution of the electronic and vibrational states for both Mn and Ga depend on the chosen relative orientation of the Mn spins across the Ga sheets in the Mn–Ga–Mn trilayers. In addition, the elastic properties have been calculated, and from the five elastic constants, the Voigt bulk modulus is determined to be 157 GPa, the Voigt shear modulus 93 GPa, and the Young's modulus 233 GPa. Furthermore, Mn2GaC is found relatively elastically isotropic, with a compression anisotropy factor of 0.97, and shear anisotropy factors of 0.9 and 1, respectively. The Poisson's ratio is 0.25. Evaluated elastic properties are compared to theoretical and experimental results for M 2 AC phases where M = Ti, V, Cr, Zr, Nb, Ta, and A = Al, S, Ge, In, S

Accelerated discovery of two crystal structure types in a complex inorganic phase field

The discovery of new materials is hampered by the lack of efficient approaches to the exploration of both the large number of possible elemental compositions for such materials, and of the candidate structures at each composition1. For example, the discovery of inorganic extended solid structures has relied on knowledge of crystal chemistry coupled with time-consuming materials synthesis with systematically varied elemental ratios2,3. Computational methods have been developed to guide synthesis by predicting structures at specific compositions4,5,6 and predicting compositions for known crystal structures7,8, with notable successes9,10. However, the challenge of finding qualitatively new, experimentally realizable compounds, with crystal structures where the unit cell and the atom positions within it differ from known structures, remains for compositionally complex systems. Many valuable properties arise from substitution into known crystal structures, but materials discovery using this approach alone risks both missing best-in-class performance and attempting design with incomplete knowledge8,11. Here we report the experimental discovery of two structure types by computational identification of the region of a complex inorganic phase field that contains them. This is achieved by computing probe structures that capture the chemical and structural diversity of the system and whose energies can be ranked against combinations of currently known materials. Subsequent experimental exploration of the lowest-energy regions of the computed phase diagram affords two materials with previously unreported crystal structures featuring unusual structural motifs. This approach will accelerate the systematic discovery of new materials in complex compositional spaces by efficiently guiding synthesis and enhancing the predictive power of the computational tools through expansion of the knowledge base underpinning them

First-principles study of structural, elastic, electronic and optical properties of perovskites hydrides XLiH

The stability, structural, elastic, electronic and optical properties of perovskite hydrides BaLiH3 and SrLiH3 were investigated by the density functional theory. The calculated lattice parameters are in well agreement with previous calculation and experimental data. The energy band structure, density of states, born effective charge and Mulliken charge population were obtained. BaLiH3 and SrLiH3 present an indirect band gap of 2.23 eV and 1.86 eV at equilibrium. The top of the valence band reflects the s electronic character for both structures. Furthermore, the absorption spectrum, refractive index, extinction coefficient, reflectivity, energy-loss spectrum and dielectric function were calculated. The origin of the spectral peaks was interpreted based on the electronic structure. The static dielectric constant and static refractive index are proportional to the fundamental indirect band gap

Structural, elastic, electronic, optical and thermal properties of cubic perovskite CsCdF

We have investigated the structural, elastic, electronic, optical and thermal properties of an insulator perovskite CsCdF3 using the pseudo-potential plane wave (PP-PW) scheme in the frame of generalized gradient approximation (GGA) and local density approximation (LDA). The computed lattice parameter and bulk modulus agree reasonably with experimental and previous theoretical works. We find that the cubic Pm-3m crystal symmetry persists throughout the pressure range studied. The anisotropy in CsCdF3 crystal is strong, while, by analyzing the ratio between the bulk and shear moduli, we conclude that CsCdF3 is ductile material. The calculations reveal that CsCdF3 is an indirect-gap insulator under ambient conditions, with the gap increasing under pressure. Also, we present the results of the densities of states and charge densities. The static dielectric constant and static refractive index are proportional to the fundamental indirect band gap Γ-R. The thermal effect on the volume, bulk modulus, heat capacities CV and CP and Debye temperature was predicted using the quasi-harmonic Debye model. To the author's knowledge, most of the studied properties are reported for the first time

Density functional prediction of the structural, elastic, electronic, and thermodynamic properties of the cubic and hexagonal (c, h)-Fe2Hf

Using density functional theory (DFT), the structural, elastic, electronic, and thermodynamic properties of Fe2Hf in the cubic and hexagonal solid phases with Fd-3m and P63/mmc are reported with generalized gradient approximations (GGA). To achieve energy convergence, we report the k-point mesh density and plane-wave energy cut-offs. The calculated equilibrium parameters are in good agreement with the available theoretical data. A complete elastic tensor and crystal anisotropies of the ultra-incompressible Fe2Hf are determined in the wide pressure range. Finally, by using the quasi-harmonic Debye Model, the isothermal and adiabatic bulk modulus and heat capacity of Fe2Hf are also successfully obtained in the present work. By the elastic stability criteria, it is predicted that Fd-3m and P63/mmc structures of Fe2Hf are stable in the pressure range studied, respectively

Structural, elastic, thermoelastic and electronic properties of M2O3 (M = Cr, Fe, Al) compounds: Experimental and theoretical study

We derived the chemical compositions and the micro hardness of the two studied steels Fe20Mn5Cr and Fe9S28Mn. The contamination of these two compounds by oxygen gives the series M2O3 (M = Fe, Cr, Al). Rhombohedral crystal structure of these compounds was determined by means of the X-rays diffraction. First principles calculations were performed to investigate structural, elastic and mechanical properties of M2O3 (M = Fe, Cr, Al) compounds at equilibrium pressure. Fe2O3 and Cr2O3 are classified as ductile materials, while Al2O3 is brittle. The Debye temperature, the elastic wave velocities and the integration of elastic wave velocities in various directions of the single crystal were obtained. All these compounds are elastically and chemically stable. The calculated elastic constants are in good agreement with the experiment values in the approximation of the gradient generalized for the correlation and exchange potential. We calculated the partial and total densities of states PDOD and TDOS for M2O3 (M = Fe, Cr, Al) compounds. As a result, electronic bands, DOS at the Fermi level, were obtained for the first time especially for Fe2O3 and Cr2O3. Keywords: Band structure, Bulk moduli, Electronic propertie