First principles study of structural, elastic, and thermodynamic properties of LiAl

The equilibrium structural parameters, thermodynamic properties, elastic constants, and several other related properties of LiMAl2 (M = Rh, Pd, Ir and Pt) ternary intermetallic compounds have been investigated, employing the projected augmented wave pseudopotentials (PAW) approach in the framework of the density functional theory (DFT) as implemented in the Quantum Espresso code. Our findings on the lattice parameters of LiMAl2 (M = Rh, Pd, Ir and Pt) compounds agree well with the experimental ones, while our obtained results of the elastic constants are in general slightly higher than the theoretical ones reported previously in literature. Our results concerning the mechanical stability criteria indicate that all LiMAl2 (M = Rh, Pd, Ir and Pt) are mechanically stable at equilibrium, while the analyses of both Zener anisotropy factor and elastic anisotropy index show that all these compounds are highly anisotropic in their elastic properties. According to Mukhanov et al.’s (Philos. Mag. 89:2117, 2009) model, the Vickers hardness HV of LiMAl2 (M = Rh, Pd, Ir and Pt) increases gradually and almost linearly with increasing pressure. The Debye temperature θD as well as the melting point Tm of the aggregate materials are calculated using two different empirical expressions. The obtained values of θD are around 499.5 (546.4) K for LiRhAl2, 478.7 (520.6) K for LiPdAl2, 411 (451) K for LiIrAl2, and 417.3 (455.2) K for LiPtAl2 compound, respectively; while those of Tm are found to be around 1566 (1448) K for LiRhAl2, 1436 (1316) K for LiPdAl2, 1650 (1502) K for LiIrAl2, and 1615 (1489) K for LiPtAl2, respectively. Our calculated data show that the behavior of the thermodynamic properties with increasing temperatures is monotonic for all our materials of interest

The pressure influence on structural parameters and elastic properties of rock-salt CaX (X=S, Se and Te) materials

The structural parameters and elastic properties of rock-salt CaX (X = S, Se and Te) materials are explored employing the CASTEP code established on the density functional theory (DFT). The energy of exchange-correlation is calculated using the generalized gradient approximation (GGA). The convention between our outcomes related to the lattice parameter and experiment is 0.50%, 0% and 1% for CaS, CaSe and CaTe materials, respectively. The lattice constant augments when proceeding from CaS to CaSe to CaTe. This lowers also the modulus of compressibility. The studied materials present a weak elastic constants for C12 and C44. This signalizes that these materials are supplementary reluctant to the unidimensionelle compression than to the perversion of cisaillement. C11 increases very rapidly. However, C12 and C44 increase very slowly. The material stability of the structure for the results of interest is stable at zero pressure. A phase transition will happen at pressures of 25.20 GPa for CaSe and 20.10 GPa for CaTe. No phase transition has been detected for CaS up to 30 GPa. All studied materials have comported as fragile in the pressure range 0 to 4 GPa. The variation of energy under any little deformity is positive. The anisotropy indicates that all materials are anisotropic in the pressure range up to 30 GPa and they are more rigid along the axes 〈100〉

First-Principles Study of Pressure Dependence of Optical Spectra of MnS

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Electronic structure and optical response for Zn1−xBexSe

The electronic structures and optical properties of the Zn1−xBexSe semiconductor ternary alloys have been investigated by using the full-potential linear augmented plane wave (FP-LAPW) method. From this study, the energy band gap has a value of about 1.2 eV for zinc-blende ZnSe. However, for Zn0.50Be0.50Se and BeSe, the fundamental band gap energy is found to occur at the highly symmetric X point in the Brillouin zone and has values of about 2.3 eV and 2.8 eV, for Zn0.50Be0.50Se and BeSe, respectively. Optical parameters, such as dielectric constant, refractive index and reflectivity are calculated and analyzed. The results demonstrated that the compounds Zn1−xBexSe have the potential to be used for optoelectronic applications. Keywords: Band structure, Optical properties, Zn1−xBexSe alloys, FP-LAPW metho

A study of CdTe solar cells using Ga-doped MgxZn1-xO buffer/TCO layers: Simulation and performance analysis

The effect of stacked Ga-doped MgxZn1−xO (GMZO) thin films being the n-partner buffer layer and of the transparent conducting oxide (TCO) layer on the performance of CdTe thin film solar cells has been investigated. The diversity of the electrical and optical properties of GMZO films versus Ga and Mg doping concentrations suggested the use of low-Ga-doped MgxZn1−xO (LGMZO) films as a high resistance transparent buffer layer. Thus, a high-Ga-doped MgxZn1−xO (HGMZO) film is nominated as a transparent TCO layer. In this respect, a (n+)-HGMZO/(n)-LGMZO/(p)-CdTe/MoTe2/Mo suggested structure has been simulated using the Analysis of Microelectronic and Photonic Structures (AMPS-1D) software under the AM1.5G illumination and at a temperature of 300 K. The structure uses the molybdenum ditelluride (MoTe2) layer as a back surface between the CdTe absorber layer and the Mo back contact. The effect of the thickness and the carrier concentration of the LGMZO-buffer, and of the CdTe absorber layers on the CdTe cell performance was investigated. Keywords: CdTe solar cells, Thin films, Ga-doped MgxZn1−xO, AMPS-1

Structural phase stability, elastic parameters and thermal properties of YN from first-principles calculation

The structural phase stability, elastic parameters and thermodynamic properties of YN at normal and under high pressure are reported. The calculations are mainly performed using the full-potential linearized augmented plane wave method within the density functional theory. Both local density approximation (LDA) and generalized gradient approximation (GGA) are used to model the correlation-exchange potential. The calculated equilibrium lattice parameter and the bulk modulus show good accordance with the experimental and previous theoretical reports. The phase transition from the NaCl (B1) structure to the CsCl (B2) structure is found to occur at 131 GPa within GGA and 115 GPa within LDA. The linear pressure coefficients of the different elastic moduli being addressed here are also determined along with the mechanical and dynamical stability criteria which are shown to be satisfied for YN with B1 phase under normal conditions. Besides, the heat capacity and other thermodynamic parameters are examined and discussed versus temperature

Phase transition, mechanical stability and optical response of MnSe: Pressure effect

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