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In this paper, by using density functional theory (DFT), the structural, electronic, and optical properties of cubic and orthorhombic perovskites BaZrS3−xSex are explored. The lattice parameters increase when the substitution of S/Se atoms is applied, whereas the bulk moduli decrease. The density of states curves showed a strong hybridization between Zr-d and S-p/Se-p orbitals. Furthermore, the obtained bandgaps of the orthorhombic phases are direct (Γ–Γ), whereas they are indirect (R–Γ) for the cubic phase. When substituting sulfur with selenium, the bandgap decreases from 0.963 to 0.705 eV for the orthorhombic phase and from 0.655 to 0.288 eV for the cubic phase. The dielectric function showed that the optical bandgaps are between 0.7 and 0.5 eV for orthorhombic BaZrS3–xSex, which is in the infra-red spectrum, and it was between 0.7 and 0.25 eV for the cubic phase. The reflectivity was in the range of [26%–31%] at low energies, which can be considered quite reflective. The refractive index for the orthorhombic phase increased from 3.0 to 3.5 at low energies and from 3.6 to 3.9 for the cubic phase, which indicates high absorption at those values of energy. The result obtained indicates that chalcogenide perovskites BaZrS3−xSex are good candidates for future photovoltaic applications such as tandem solar cells. [ABSTRACT FROM AUTHOR]

In this article, the structural, elastic, electronic, and magnetic characteristics of both regular and inverse Heusler alloys, Sc2TiAl and Sc2TiSi, were investigated using a full-potential, linearized augmented plane-wave (FP-LAPW) method, within the density functional theory. The optimized structural parameters were determined from the minimization of the total energy versus the volume of the unit cell. The band structure and DOS calculations were performed within the generalized gradient approximation (GGA) and modified Becke–Johnson approaches (mBJ-GGA), employed in the Wien2K code. The density of states (DOS) and band structure (BS) indicate the metallic nature of the regular structure of the two compounds. The total spin magnetic moments for the two compounds were consistent with the previous theoretical results. We calculated the elastic properties: bulk moduli, B , Poisson's ratio, ν , shear modulus, S, Young's modulus (Y), and the B/s ratio. Additionally, we used Blackman's diagram and Every's diagram to compare the elastic properties of the studied compounds, whereas Pugh's and Poisson's ratios were used in the analysis of the relationship between interatomic bonding type and physical properties. Mechanically, we found that the regular and inverse full-Heusler compounds Sc2TiAl and Sc2TiSi were stable. The results agree with previous studies, providing a road map for possible uses in electronic devices. [ABSTRACT FROM AUTHOR]

The structural, elastic, electronic, magnetic, and thermoelectric properties of MgEu2X4 (X = S and Se) spinel compounds are investigated computationally. Calculations are performed using the full‐potential linearized augmented plane wave (FP‐LAPW) method within the Perdew, Burke, and Ernzerhof generalized gradient approximation (PBE‐GGA), GGA + U, and modified Becke–Johnson (mBJ‐GGA) approximations. The band structure and density of states results from the three exchange‐correlation approximation methods (mBJ, GGA + U, and PBE) show that these spinel compounds are fully spin‐polarized. Also, they possess a half‐metallic character in the spin‐down channel with a direct bandgap (Γ–Γ) of about 3.44, 2.712, and 2.472 eV for MgEu2S4 and 2.89, 2.285, and 2.017 eV for MgEu2Se4, respectively. The formation of both compounds is energetically favorable based on the results of the total energy and cohesive energy calculations. Furthermore, the two compounds are chemically and mechanically stable, as concluded from cohesive energy and elastic calculations. The elastic calculations reveal that both spinel compounds are ductile materials. The ionic bonds are predominant. The quasi‐harmonic model has also been used to investigate the influences of temperature and pressure on thermal characteristics. The thermoelectric behavior is studied using the BoltzTraP code. Both systems show good thermoelectric properties for the spin‐down channel. [ABSTRACT FROM AUTHOR]

Density functional theory calculations based on full potential linearized augmented plane-wave (FP-LAPW) plus local orbital method in the framework of GGA-PBE, as embodied in the WIEN2k code, is used to investigate the structural, electronic and magnetic properties of intermetallic T i 1 + x F e S b Heusler compounds, where ( x = − 0.75 , − 0.50 , − 0.25 , 0.0 , 0.25 , 0.50 , 0.75 , 1.0 ). Moreover, the Tran-Blaha parameterized of the modified Becke-Johnson (TB-mBJ) exchange potential, as a semi-local method, is employed to predict the bandgap more precisely. The physical characteristic of these systems are found to be mostly determined by the crystal structure and the electron concentration or the number of valence electrons. We examined the site preference of the parent compound T i F e S b and varied the electron concentration by doping or removing a T i atom and we found that the variation plays a crucial role in the physical properties of these material systems. Alloys with x ≤ 0 are found to exhibit a ferrimagnetic phase, and the alloy with x = 0.25 exhibits non-magnetic properties, whereas the rest have shown ferromagnetic phase. The band-structure analysis of T i 1.75 F e S b and T i 2 F e S b ( C u H g 2 T i -type) alloys suggested that they could be ferromagnetic half-metallic candidates with bandgaps 0.350 and 0.468 eV, respectively. We found that T i rich T i 1 + x F e S b alloys have high spin polarization. [ABSTRACT FROM AUTHOR]