- [ VRPG-Doc-Sc] Sciences physiques --- علوم فيزيائية
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- ItemEtude du premier principe des propriétés structurales, électroniques, et magnétiques de la nouvelle classe des alliages Heusler(2016-02-25) KHETIR Mohammed Amine; Encadreur: Rozale Habib; Co-Encadreur: LAKDJA Abdelazizالملخص (بالعربية) : :ملخص إنّ مجموعة من المعادن المسمات خلائط هسلار قد تم التنبوء أنّها تحمل خصائص أنصاف المعادن عند درجة حرارة معتدلة من أهم الميادين التي تستعمل فيها هي سبين ترونيك لانّها تملك درجة حرارة كوري عالية و إستقطاب قد يصل إلى مائة بالمائة و مجموعة معادن نصف هسلار الفيرومغناطيسي حضي بدراستنا في هادا العمل نقدم دراسة نظرية لهده المواد باستعمال طريقة المبدء الإول أبينسيو و طريقة إستغلال المعلومات و دالك لمعاينة الخصائص الهيكلية و الإلكترونية و المغنطيسية لهذه المواد Résumé (Français et/ou Anglais) : Abstract In search of half-metallic ferromagnetism, we have studied the electronic structure and magnetic properties based on density functional theory (DFT) within the generalized gradient approximation (GGA) and GGA plus modified Becke and Johnson as the exchange correlation for XCsSr (X = C, Si, Ge, and Sn) half-Heusler compounds. The strong spin polarization of p orbital for C, Si, Ge, and Sn atoms is found to be the origin of ferromagnetic for all compounds leading to a total magnetic moment 1 µB. Résumé: Dans le domaine de recherche du ferromagnétisme semi métallique, on a fait l’étude structurale électronique et magnétique du composé hypothétique XCsSr ( X= C, si, Sn et Ge) en utilisant la méthode ( DFT) la théorie de la fonctionnelle de la densité avec l’approximation du gradient généralisé (GGA) et la GGA + MBj, et la forte polarisation en spin des orbitales p des Atomes C, Ge, Sn, et Si s’avers l’origine de l’état fondamental ferromagnétique conduisant à moment magnétique total égal à 1 µB.
- ItemL'étude de l'effet multi-échelle de nouveaux matériaux et applications technologiques(2017-07-04) KHEROUBI Boumediene; Encadreur: BENZAIR AbdelnourAbstract In this work we examine the role of the multi-scale effect in the study of physical properties in the behavior of new materials and the discussions that generate on the link of atomic simulations. Theoretical effect is defined through modes of structural instability that are specified by criteria involving adjustable parameters. More, usually force can be characterized by the appearance of soft mode. Keys words: multi-scale effect, new materials, technologic application Résumé Dans ce travail de thèse nous examinons le rôle de l'effet multi échelle à l'étude des propriétés physique dans le comportement de nouveaux matériaux et les discussions qui engendrent sur le lien des simulations atomistiques. Effet théorique est défini grâce à des modes de l'instabilité structurelle qui sont spécifiés par des critères impliquant des paramètres ajustable. Plus, généralement la force peut être caractérisée par l'apparition de soft mode. Mots clés: effet multi-échelle, nouveaux matériaux, application technologique.
- ItemÉtude des propriétés structurales, électroniques, élastiques, magnétiques et thermodynamiques des composés Full-Heusler X2CeAl (X= Ag, Cu et Au)(2018-12-06) Khelfaoui Friha; Encadreur: Ameri MohammedRésumé (Français et Anglais) : Résumé L’objectif de ce travail est d’étudier les propriétés structurales, électroniques, élastiques, magnétiques, et thermodynamiques des matériaux Heusler. Pour ce faire, on a visé les composés ternaires X2CeAl avec X=Ag, Cu, and Au. En effet, on a utilisé la théorie de la fonctionnelle de la densité (DFT) avec l’approximation du gradient généralisé (GGA-PBE). On note que ces composés ont l’élément terre rare lourd Ce qui nous emmène à ajouter la correction de couplage spin-orbit dans cette approximation (GGA+SOC). Les paramètres de maille des composés étudiés à l’état fondamental sont les premières prédictions. L’analyse des résultats des bandes d’énergie et des densités d’états des composés ternaires X2CeAl montre que ces matériaux sont des métaux ferromagnétiques et que l’élément Ce est principalement l’origine de magnétisme de ces matériaux. Abstract The aims of this work is to studied the structural, elastic, electronic, magnetic, elastic and thermodynamic properties of the Full Heusler compounds X2CeAl with X=Ag, Cu, and Au. In effect, we used The density functional theory (DFT) with the generalized gradient approximation (GGA-PBE).Their inclusion of the heavy and rare earth element Ce leads us to add the spin-orbit coupling correction (GGA+SOC). The calculated lattice parameters corresponding to the ground state are the first predictions. There are no available experimental and theoretical results to compare with. Analysis of the results of the energy bands and density of states of the ternary compounds X2CeAl shows that these materials are the ferromagnetic metals and Ce atom is the origin of their ferromagnetism.
- ItemEtude ab initio des propriétés structurales, mécaniques, électroniques et thermiques des composés Fe2VX (X = Al, Ga) sous pression.(2016-07-03) KHALFA MOHAMED; Encadreur: KHACHAI HOUARIRésumé (Français et/ou Anglais) : The electronic structure, mechanical and thermodynamic properties of Fe2VX, (with X = Al and Ga), have been studied self consistently by employing state-of-the art full-potential linearized approach of augmented plane wave plus local orbitals (FP-LAPW+lo) method. The exchange-correlation potential is treated with the local density and generalized gradient approximations (LDA and GGA). Our predicted ground state properties such as lattice constants, bulk modulus and elastic constants appear more accurate when we employed the GGA rather than the LDA, and these results are in very good agreement with the available experimental and theoretical data. Further, thermodynamic properties of Fe2VAl and Fe2VGa are predicted with pressure and temperature in the ranges of 0–40 GPa and 0–1500 K using the quasi-harmonic Debye model. We have obtained successfully the variations of the heat capacities, primitive cell volume and volume expansion coefficient. Keywords: DFT, electronic structure, mechanical properties, thermodynamic properties, Heusler compounds.
- ItemContribution à l’étude des propriétés physiques de l’alliage CuCl1-xBrx (0≤ x ≤ 1) par la méthode FP - LMTO(2016-12-15) KAMEL M’rabet; Encadreur: AMERI Mohammed; Co-Encadreur: ABIDRI BoualemRésumé (Français et/ou Anglais) : This work is a contribution to the study of structural, elastic, electronics, optics and thermodynamics, materials of the I-VII (copper halides) and the ternary alloy derived from these compounds, this summer to study by the muffin-tin orbital method linearized with a total potential (FP-LMTO) as part of the functional theory of DFT density, implemented in the code Mstudio Mindlab, and to determine the potential for exchange and correlation is used the approximations of the generalized gradient (GGA). In this work, we have 1first ground state, the structural properties of CuX (CuCl, CuBr) after calculating the transition pressure we note that the most stable phase and the zinc-blende phase (B3) and vien computing elastic properties of binary compounds in their phase (B3). the lattice parameter, the elastic modulus and its derivative were calculated and compared, are in good agreement with experimental and other theoretical results. The elastic constants are close to the experimental data . One of the most important aspects of our calculations is that brings out the important role played by the state (d) of the transition metal (Cu) which states p boron atom are absent. In the GGA approach, we studied the electronic properties (band structure, charge density and effective mass) of the parent compounds. The detailed study of the state total and partial density allowed us to determine the type of hybridization of the orbital and clarify the participation of each band in the link that give the good nature of the energy gap. The compounds exhibit a mixed character of ionic and covalent bonding and the semiconductor behavior to direct band gap Γ-Γ. The elastic coefficients predicted by the model Mehl show that our materials are stable in this phase of zinc-blende structure and values are closest to the experiment. Our study has established stability and physical properties of the CuCl1-x Brx alloy was used for the first time Züger technique to study the origin of the optical bowing. The chemical contribution (Charge) is more important than the structural effects and volumetric strain due to the small difference in ionicity Between the two parent compounds. The optical parameters are processed by code Mstudio Mindlab. Quasi-harmonic Debye model, wherein the crystal vibrations are Treated as a continuum isotope obtained from derivative energy total electron relative to the volume. This model provides results fundamentally correct and reasonable and in good agreement with experiment, we show that the coefficient of thermal expansion (α) increases with increasing temperature. θD It is noted that decreases linearly with increasing temperature. For a fixed temperature, the Debye temperature increases with increasing pressure. In conclusion, the dependencies of volume compressibility modulus, heat capacities and temperature on the Debye temperature and pressure were successfully obtained.
