Search

Effect of functional on structural, elastic, optoelectronic and thermoelectric characteristics of semiconducting MgX2Se4 (X = Lu, Y) spinels has been realized by WIEN2k code. The lattice constant of MgY2Se4 is slightly greater than that of MgLu2Se4, and these quantities are slightly deviated from the experimental values, where the error does not exceed 1.3%. The cohesive energy proves that both spinels are chemically stable in the normal case, and this stability is more pronounced in MgLu2Y4. The large ionic radius of Lu compared to Y explains the high bulk modulus of MgY2Se4 as well as its hardness. The spinels under study have Г → Г direct band gap located between 1.178 and 1.4 eV for all the functionals, proving their semiconductor nature. Se-s, Y-d, Lu-d states in MgY2Se4 and MgLu2Se4 dominate the upper valence band, while the first conduction band located between Fermi level and 1.5 eV is empty. There is a strong coupling between Se-p–Lu-p sites for MgLu2Se4 and Se-p–Y-p states in MgY2Se4, which reflects their hybridization. The high absorption in the ultraviolet range, the band gap between 1 and 2.4 eV and the refractive index in the range of 2.29–2.61 favour these spinels as absorbers in solar cells. Peaks of all the optical quantities studied relating to the mBJ–GGA functional are shifted to the right compared with GGA and GGA+SO approximations. The thermoelectric parameters were investigated as a function of photon energy and temperature using GGA+SO functional. [ABSTRACT FROM AUTHOR]

The main objective of this research is the explanation of the replacement of feldspar limestone imported from Spain with recycled automotive glass, in order to reduce waste and promote environmental sustainability. Details and efforts of making porcelain ceramics from local raw materials such as quartz, kaolin and glass are also given. Replacing the feldspar with reclaimed automotive glass shows the effect of the Na2O and CaO solvents contained in the glass on the sintering and crystallization of the studied porcelain. The results showed that the added glass contributes to the reduction of the density and the acceleration of the sintering process, by occupying the sites of the open spaces, observed in the samples not containing feldspars. By reaching a nonporous ratio at a temperature of 1000∘C, the melting of the material is accelerated due to the dissolved oxides it contains, in addition to the linear shrinkage rate in samples that contain a lot of glass reaching the normal level of porcelain (about 12%) at low temperature compared to ordinary porcelain. [ABSTRACT FROM AUTHOR]

Structural, elastic, mechanical and electronic properties of pure and zinc-doped SrTiO3 at the concentration in the range (1–10%) are studied by first-principles calculations. The structural parameters of synthesized compounds agree well with the standard data depicting the growth of stable compounds. A slight obvious increase in the lattice constant of 3.9245 Å is observed in Zn-doped SrTiO3 due to the deviation of the atomic radii of Zn and Ti. Elastic constants and mechanical parameters of SrTiO3 are closer to their available theoretical and experimental data. The investigated compounds exhibit brittle behavior for all Zn ratios. The doping zinc concentration reduces the indirect band gap value. The doping concentration 2%, gives a band gap value closer to the experimental one. The band gap of pure SrTiO3 is 1.827 eV and after doping with Zn for concentration from 1% to 10%, the optimized values are 1.970, 1.886, 1.802, 1.718, 1.635, 1.552, 1.470, 1.389, 1.310, 1.231 and 1.154 eV. [ABSTRACT FROM AUTHOR]

We carried out a theoretical study on hexahalometallate single crystals X2SnBr6 (X = Rb, Cs) with the density functional theory framework, using generalized gradient approximation of the Perdew, Burke, and Ernzerhof and Heyd–Scuseria–Ernzerhof hybrid functional. The lattice constant of the compounds Cs2SnBr6 and Rb2SnBr6 is consistent with the experimental data currently available, with an uncertainty of 0.04% and 0.07%, respectively. For the first time, the elastic moduli of Cs2SnBr6 at equilibrium and under pressure effect were estimated. When fitted to the Birch–Murnaghan equation of state, the bulk modulus of Cs2SnBr6 and Rb2SnBr6 obtained using the generalized gradient approximation optimization is closer to the experimental one. The interatomic distances of Cs2SnBr6 are greater than those of Rb2SnBr6, because these distances are proportional to the radius of Cs (1.73 Å) and Rb (1.64 Å). The direct band gap Γ–Γ of 1.272 eV and 1.1019 eV for, respectively, Cs2SnBr6 and Rb2SnBr6 explains their semiconducting character. The Sn-s state dominates in the conduction band minima, indicating that Sn and Br are in ionic connection in both Cs2SnBr6 and Rb2SnBr6 [ABSTRACT FROM AUTHOR]

The structural, elastic, electrical, and thermodynamic characteristics of Fe2Hf cubic and hexagonal phases with space group Fd-3m and P63/mmc are presented using the generalized gradient approximations. The k-points mesh density and plane-wave energy cut-off accomplish the energy convergence. The computed equilibrium parameters are closer to the theoretical data. The elastic tensor and crystal anisotropy of ultraincompressible Fe2Hf are computed in a wide pressure range. The isothermal and adiabatic bulk modulus, as well as the heat capacity of Fe2Hf is successfully calculated utilizing the quasi-harmonic Debye Model. The Fd-3m and P63/mmc Fe2Hf structures are stable in the studied pressure range. [ABSTRACT FROM AUTHOR]

Some physical properties of hexahalometallate K2XBr6(X = Se, Pt) were computed in the zinc blend structure using GGA-PBESOL. The cell constant of K2SeBr6 and K2PtBr6 is consistent to the experiment value quoted in the literature, where the error is 0.95% and 1%. K2SeBr6 and K2PtBr6 present covalent bonding, high anisotropy and are ductile. The elastic constants of K2SeBr6 and K2PtBr6 are significantly smaller due to their larger reticular distances, lower Coulomb forces and then they are soft and damage tolerant. The interatomic separation is greater in K2SeBr6 than in K2PtBr6, hence the Coulomb interaction in K2PtBr6 is greater than that of K2SeBr6. The internal coordinate of Br atom in K2PtBr6 is lower than that of the same atom in K2SeBr6, and this can be explained by the fact that it is inversely proportional to the atom radius of Se and Pt. There are two major plasmonic processes, with intensities 3.7 and 1.35 located around 53.5 nm and 72.8 nm for K2SeBr6 and K2PtBr6. [ABSTRACT FROM AUTHOR]