Ab initio Study of Some Physical Properties of the Cu2MgSiS4 and Cu2MgGeS4 diamond-like semiconductors and Sr2GeN2 Polymorphs / BEDJAOUI Abdelhak  

Public ISBD Titre : Ab initio Study of Some Physical Properties of the Cu2MgSiS4 and Cu2MgGeS4 diamond-like semiconductors and Sr2GeN2 Polymorphs Type de document : texte imprimé Auteurs : BEDJAOUI Abdelhak, Auteur Editeur : Setif:UFA Année de publication : 2017 Importance : 1 vol (187 f .) Format : 29 cm Langues : Français (fre) Catégories : Thèses & Mémoires:Physique Mots-clés : Diamond-like compound Sr2GeN2 polymorphs First-principles calculations structural parameters Elastic moduli Electronic structure  Optical properties  thermodynamic properties Index. décimale : 530 Physique Résumé : In the present work, we have explored some physical properties of the two newly synthetized quaternary diamond-like semiconductors Cu2MgSiS4 and Cu2MgGeS4, and two polymorphs of the ternary nitrides α-Sr2GeN2 and β-Sr2GeN2, using firstprinciple calculations based on the density functional theory (DFT). The exchange-correlation effects were treated within the new version of the generalized gradient approximation (GGA-PBEsol). The structural, elastic, electronic and optical properties of the two considered diamond-like semiconductors were studied in detail using two complementary first-principles approaches: the pseudopotential plane wave (PP-PW) and the full potential augmented plane wane (FP-LAPW). The calculated equilibrium structural parameters are in good agreement with the available experimental data. Single-crystal and polycrystalline elastic moduli and their related properties, including elastic constants, bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, elastic anisotropy indexes, Pugh’s criterion, elastic wave velocities and Debye temperature, were predicted. We find that the inclusion of the electronic exchange-correlation through the newly developed TB-mBJ improves the description of the electronic structure. The TB-mBJ yields a direct band gap (Γ-Γ) of 2.64 and 1.54 eV for Cu2MgSiS4 and Cu2MgGeS4, respectively. Frequency-dependence of the dielectric function, refractive index, extinction coefficient, absorption coefficient, reflectivity, energy loss function and optical conductivity were predicted, and the origins of the observed electronic transitions were assigned. Both Cu2MgSiS4 and Cu2MgGeS4 exhibit noticeable absorption in the ultraviolet range. The structural, elastic and thermodynamic properties of the α (tetragonal) and β (orthorhombic) polymorphs of the Sr2GeN2 compound have been examined in detail using ab initio pseudopotential plane-wave calculations. Apart the structural properties at ambient conditions, all present reported results are predicted for the first time. The calculated equilibrium lattice parameters and inter-atomic bond-lengths of the considered polymorphs are in good agreement with the available experimental data. It is found that α-Sr2GeN2 is energetically more stable than β-Sr2GeN2. The two examined polymorphs are very similar in their crystal structures and have almost identical local environments. The single-crystal and polycrystalline elastic parameters and related properties, including elastic constants, bulk, shear and Young’s moduli, Poisson’s ratio, anisotropy indexes, Pugh’s criterion, elastic wave velocities and Debye temperature, have been predicted. Temperature and pressure dependence of some macroscopic properties - including the bulk modulus, volume thermal expansion coefficient, heat capacity and Debye temperature - have been evaluated using ab initio calculations combined with the quasi-harmonic Debye model. Côte titre : DPH/0207 En ligne : https://drive.google.com/file/d/1znqhYjJAUf5xV_vYR8ftRwURwdDlL9eJ/view?usp=shari [...] Format de la ressource électronique : pdf Ab initio Study of Some Physical Properties of the Cu2MgSiS4 and Cu2MgGeS4 diamond-like semiconductors and Sr2GeN2 Polymorphs [texte imprimé] / BEDJAOUI Abdelhak, Auteur . - [S.l.] : Setif:UFA, 2017 . - 1 vol (187 f .) ; 29 cm. Langues : Français (fre) Catégories : Thèses & Mémoires:Physique Mots-clés : Diamond-like compound Sr2GeN2 polymorphs First-principles calculations structural parameters Elastic moduli Electronic structure  Optical properties  thermodynamic properties Index. décimale : 530 Physique Résumé : In the present work, we have explored some physical properties of the two newly synthetized quaternary diamond-like semiconductors Cu2MgSiS4 and Cu2MgGeS4, and two polymorphs of the ternary nitrides α-Sr2GeN2 and β-Sr2GeN2, using firstprinciple calculations based on the density functional theory (DFT). The exchange-correlation effects were treated within the new version of the generalized gradient approximation (GGA-PBEsol). The structural, elastic, electronic and optical properties of the two considered diamond-like semiconductors were studied in detail using two complementary first-principles approaches: the pseudopotential plane wave (PP-PW) and the full potential augmented plane wane (FP-LAPW). The calculated equilibrium structural parameters are in good agreement with the available experimental data. Single-crystal and polycrystalline elastic moduli and their related properties, including elastic constants, bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, elastic anisotropy indexes, Pugh’s criterion, elastic wave velocities and Debye temperature, were predicted. We find that the inclusion of the electronic exchange-correlation through the newly developed TB-mBJ improves the description of the electronic structure. The TB-mBJ yields a direct band gap (Γ-Γ) of 2.64 and 1.54 eV for Cu2MgSiS4 and Cu2MgGeS4, respectively. Frequency-dependence of the dielectric function, refractive index, extinction coefficient, absorption coefficient, reflectivity, energy loss function and optical conductivity were predicted, and the origins of the observed electronic transitions were assigned. Both Cu2MgSiS4 and Cu2MgGeS4 exhibit noticeable absorption in the ultraviolet range. The structural, elastic and thermodynamic properties of the α (tetragonal) and β (orthorhombic) polymorphs of the Sr2GeN2 compound have been examined in detail using ab initio pseudopotential plane-wave calculations. Apart the structural properties at ambient conditions, all present reported results are predicted for the first time. The calculated equilibrium lattice parameters and inter-atomic bond-lengths of the considered polymorphs are in good agreement with the available experimental data. It is found that α-Sr2GeN2 is energetically more stable than β-Sr2GeN2. The two examined polymorphs are very similar in their crystal structures and have almost identical local environments. The single-crystal and polycrystalline elastic parameters and related properties, including elastic constants, bulk, shear and Young’s moduli, Poisson’s ratio, anisotropy indexes, Pugh’s criterion, elastic wave velocities and Debye temperature, have been predicted. Temperature and pressure dependence of some macroscopic properties - including the bulk modulus, volume thermal expansion coefficient, heat capacity and Debye temperature - have been evaluated using ab initio calculations combined with the quasi-harmonic Debye model. Côte titre : DPH/0207 En ligne : https://drive.google.com/file/d/1znqhYjJAUf5xV_vYR8ftRwURwdDlL9eJ/view?usp=shari [...] Format de la ressource électronique : pdf

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Code-barres	Cote	Support	Localisation	Section	Disponibilité
DPH/0207	DPH/0207	Thèse	Bibliothéque des sciences	Anglais	Disponible Disponible

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