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Ab initio Study of Some Physical Properties of the Cu2MgSiS4 and Cu2MgGeS4 diamond-like semiconductors and Sr2GeN2 Polymorphs / BEDJAOUI Abdelhak
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 propertiesIndex. 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 : 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 propertiesIndex. 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 : Exemplaires (1)
Code-barres Cote Support Localisation Section Disponibilité DPH/0207 DPH/0207 Thèse Bibliothéque des sciences Anglais Disponible
DisponibleStudy of Fundamental Physical Properties of Some Ternary Nitride-Based Compounds (Ca5Si2N6 and Sr5Ge2N6) / Loubna Debache
Titre : Study of Fundamental Physical Properties of Some Ternary Nitride-Based Compounds (Ca5Si2N6 and Sr5Ge2N6) Type de document : texte imprimé Auteurs : Loubna Debache ; Youcef Medkour, Directeur de thèse Editeur : Sétif:UFA1 Année de publication : 2024 Importance : 1 vol (88 f .) Format : 29 cm Catégories : Thèses & Mémoires:Physique Mots-clés : Ternary nitrides Density functional theory GGA-PBEsol TB-mBJ Elastic
properties Electronic band structure Optical properties Transport properties Thermodynamic
propertiesIndex. décimale : 530 Physique Résumé : Our work consists in studying the structural, elastic, electronic, optical, thermoelectric
and thermodynamic properties of the ternary nitrides Ca5Si2N6 and Sr5Ge2N6, using the
density functional theory (DFT) within the GGA-PBEsol and TB-mBJ approaches. The
theoretically predicted lattice parameters constants are consistent with the available
experimental results. According to the estimated cohesive energy, formation enthalpy and
Born-Huang stability criterion, the examined compounds are thermodynamically and
mechanically stable. Findings on elastic properties suggest that both nitrides are ductile in
nature with significant elastic anisotropy. Using the TB-mBJ electronic band structure, these
nitrides were found to be semiconductors with a direct band gap (V-V) of 3.55 eV for
Ca5Si2N6 and indirect band gap (V-Γ) of 3.15eV for Sr5Ge2N6. The nitridosilicate compound
can be used as a phosphor material because the band gap and Deby temperature values are
within the recommended range. Substitution with heavier cations leads to narrowing the Eg
value and reducing the Ï´D(K) value. Even that, this material is still useful for other optical
applications. The computed optical functions show a modest static dielectric, a notable optical
anisotropy and a strong absorptivity of electromagnetic waves in the ultraviolet range,
indicating that the title compounds are suitable for UV-optoelectronic applications.
Furthermore, transport properties, including Seebeck coefficient, electrical conductivity,
thermal conductivity, power factor and figure of merit have been studied employing classical
BoltzTrap software. The large figure of merit (ZT) values of these ternary nitrides, suggests
their potential use in thermoelectric devices, especially at low and room temperature. Using
Debye's quasi-harmonic model, we explored the thermodynamic properties of Ca5Si2N6 and
Sr5Ge2N6 under the effect of temperature and pressure such as: the modulus of compressibility
B, coefficient of thermal expansion α, heat capacity at constant volume CV, heat capacity at
constant pressure CP and the Debye temperature Ï´D(K)Côte titre : DPH/0298 En ligne : http://dspace.univ-setif.dz:8888/jspui/retrieve/8476/2309.pdf Format de la ressource électronique : Study of Fundamental Physical Properties of Some Ternary Nitride-Based Compounds (Ca5Si2N6 and Sr5Ge2N6) [texte imprimé] / Loubna Debache ; Youcef Medkour, Directeur de thèse . - [S.l.] : Sétif:UFA1, 2024 . - 1 vol (88 f .) ; 29 cm.
Catégories : Thèses & Mémoires:Physique Mots-clés : Ternary nitrides Density functional theory GGA-PBEsol TB-mBJ Elastic
properties Electronic band structure Optical properties Transport properties Thermodynamic
propertiesIndex. décimale : 530 Physique Résumé : Our work consists in studying the structural, elastic, electronic, optical, thermoelectric
and thermodynamic properties of the ternary nitrides Ca5Si2N6 and Sr5Ge2N6, using the
density functional theory (DFT) within the GGA-PBEsol and TB-mBJ approaches. The
theoretically predicted lattice parameters constants are consistent with the available
experimental results. According to the estimated cohesive energy, formation enthalpy and
Born-Huang stability criterion, the examined compounds are thermodynamically and
mechanically stable. Findings on elastic properties suggest that both nitrides are ductile in
nature with significant elastic anisotropy. Using the TB-mBJ electronic band structure, these
nitrides were found to be semiconductors with a direct band gap (V-V) of 3.55 eV for
Ca5Si2N6 and indirect band gap (V-Γ) of 3.15eV for Sr5Ge2N6. The nitridosilicate compound
can be used as a phosphor material because the band gap and Deby temperature values are
within the recommended range. Substitution with heavier cations leads to narrowing the Eg
value and reducing the Ï´D(K) value. Even that, this material is still useful for other optical
applications. The computed optical functions show a modest static dielectric, a notable optical
anisotropy and a strong absorptivity of electromagnetic waves in the ultraviolet range,
indicating that the title compounds are suitable for UV-optoelectronic applications.
Furthermore, transport properties, including Seebeck coefficient, electrical conductivity,
thermal conductivity, power factor and figure of merit have been studied employing classical
BoltzTrap software. The large figure of merit (ZT) values of these ternary nitrides, suggests
their potential use in thermoelectric devices, especially at low and room temperature. Using
Debye's quasi-harmonic model, we explored the thermodynamic properties of Ca5Si2N6 and
Sr5Ge2N6 under the effect of temperature and pressure such as: the modulus of compressibility
B, coefficient of thermal expansion α, heat capacity at constant volume CV, heat capacity at
constant pressure CP and the Debye temperature Ï´D(K)Côte titre : DPH/0298 En ligne : http://dspace.univ-setif.dz:8888/jspui/retrieve/8476/2309.pdf Format de la ressource électronique : Exemplaires (1)
Code-barres Cote Support Localisation Section Disponibilité DPH/0298 DPH/0298 Thèse Bibliothéque des sciences Anglais Disponible
Disponible