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46. An ab initio study of the structural, elastic, electronic, optical properties and phonons of the double perovskite oxides Sr2AlXO6 (X=Ta, Nb, V).

Author

Ghebouli, B., Ghebouli, M.A., Choutri, H., Fatmi, M., Chihi, T., Louail, L., Bouhemadou, A., Bin-Omran, S., Khenata, R., and Khachai, H.

Subjects
*PEROVSKITE, *OPTICAL properties of semiconductors, *BAND gaps, *DIELECTRICS, *DENSITY functional theory, *AB initio quantum chemistry methods
Abstract

We report ab initio density functional theory calculations of the structural, elastic, electronic and optical properties of the double perovskite oxides Sr 2 AlXO 6 (X=Ta, Nb, V). We have predicted a direct Г–Г band gap in Sr 2 AlXO 6 (X=Ta, Nb) and an indirect Г–X band gap for Sr 2 AlVO 6 . The fundamental band gap increases linearly when the pressure is enhanced in the range 0–20 GPa. The frequency dependent of complex dielectric function, absorption, reflectivity and electron energy loss function were investigated in the range 0–40 eV. Features such as lattice constant, bulk modulus, elastic constants, band structure, total and local densities of states have been computed. [ABSTRACT FROM AUTHOR]

Published
2016
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47. Electronic structure and lattice dynamics of Ca x Mg1−x S in the rock-salt phase.

Author

Ghebouli, M.A., Choutri, H., and Bouarissa, N.

Subjects
*CALCIUM sulfide, *CRYSTAL lattices, *MAGNESIUM compounds, *ROCK salt, *ELECTRONIC band structure, *LATTICE dynamics, *NUMERICAL calculations
Abstract

Abstract: Electronic band structure and lattice dynamical properties of Ca x Mg1−x S alloys in the rock-salt phase have been investigated. The calculations are performed in the framework of ab initio pseudo-potential approach within the generalized gradient approximation. Reasonable agreement is generally obtained between our results and the available experimental observations and previous calculations. The deviation of the alloy lattice constant and bulk modulus from linearity has been examined and discussed. Fundamental band gaps and Г–X and Г–L separations in higher-lying conduction bands are predicted. In agreement with reflectivity spectrum and recent optical absorption spectrum measurements, CaS in the rock-salt phase is found to be an indirect band-gap (Г–X). Similarly to CaS, the electronic band structure calculations showed that MgS is also an indirect band-gap (Г–X) semiconductor. However, a system transition between indirect and direct structures has been predicted in the Ca concentration range 0.12–0.83. Upon alloying the phonon modes are significantly changed showing that the longitudinal optical–transverse optical (LO–TO) splitting becomes narrower as one proceeds from pure rock-salt MgS to pure rock-salt CaS. [Copyright &y& Elsevier]

Published
2014
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48. Lattice dynamics and thermal properties of Ca x Mg 1−x S ternary alloys

Author

Choutri, H., Ghebouli, M.A., and Bouarissa, N.

Subjects
*LATTICE dynamics, *CALCIUM compounds, *THERMAL properties of metals, *TERNARY alloys, *CRYSTAL structure, *PERMITTIVITY, *HEAT capacity
Abstract

Abstract: We present results of ab initio calculations concerning lattice dynamical and thermal properties of MgS, CaS and their ternary mixed crystals Ca x Mg 1−x S in zinc-blende structure. Results for the phonon modes, dielectric constants, Fröhlich coupling parameter, polaron effective mass, entropy and heat capacities are given for Ca x Mg 1−x S within a composition range 0–1. Generally good agreement is obtained between our results and data available in the literature. Other case, our results are predictions. [Copyright &y& Elsevier]

Published
2013
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49. Theoretical prediction of the fundamental properties for the ternary Li2PtH6 and Na2PtH6

Author

Ghebouli, M.A., Choutri, H., Bouarissa, N., Ghebouli, B., Bouhemadou, A., Soyalp, F., Uçgun, E., and Ocak, H.Y.

Subjects
*LITHIUM compounds, *TERNARY system, *SODIUM compounds, *HYDROGEN storage, *OPTICAL properties, *DENSITY functionals, *ELECTRONIC structure
Abstract

Abstract: Li2PtH6 and Na2PtH6 are good candidate for hydrogen storage. The structural, elastic, electronic and optical properties of Li2PtH6 and Na2PtH6 compounds have been investigated using pseudo-potential plane–wave method based on the density functional theory. Computed lattice constant and H atom positional parameter at equilibrium agree well with the available experimental data. A quadratic pressure dependence of the elastic stiffness is found. A set of isotropic elastic parameters and related properties, namely bulk and shear moduli, Young''s modulus, Poisson''s ratio, average sound velocity and Debye temperature are numerically estimated in the framework of the Voigt–Reuss–Hill approximation for Li2PtH6 and Na2PtH6 polycrystalline aggregate. The analyses of the band structure indicates that Li2PtH6 and Na2PtH6 are indirect gap semiconductors. The static dielectric constant and static refractive index are inversely proportional to the fundamental gap. [Copyright &y& Elsevier]

Published
2012
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50. First-principles study on stability, energy gaps, optical phonon and related parameters of In1−x−y Al x Ga y As alloys

Author

Ghebouli, M.A., Choutri, H., Bouarissa, N., and Ghebouli, B.

Subjects
*BAND gaps, *PHONONS, *INDIUM alloys, *CHEMICAL systems, *DENSITY functionals, *CHEMICAL stability, *CRYSTAL lattices, *PERMITTIVITY
Abstract

Abstract: Based on the density functional theory as implemented in the Abinit code under the virtual crystal approximation, the lattice constant, bulk modulus, elastic constants, gap energies, electron effective mass, the dielectric constants and born effective charge in In1−x−y Al x Ga y As have been calculated with both GGA and LDA in the range 0≤y≤0.9801. The optical and acoustical phonon frequencies, Fröhlich coupling parameter, deformation energy and polaron effective mass are calculated and their dependence on the Ga content is examined. For AlAs, our results are in reasonable agreement with the known data in the literature; while for other contents our treatments are predictions. [Copyright &y& Elsevier]

Published
2012
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