Titre :	Investigation on the structural, elastic, electronic and optical properties of BaTiO₃: An ab initio study
Type de document :	document électronique
Auteurs :	Kawter Ben Amara, Auteur ; Amer Saoudi, Directeur de thèse
Editeur :	Setif:UFA
Année de publication :	2025
Importance :	1 vol (80 f.)
Format :	29 cm
Langues :	Anglais (eng)
Catégories :	Thèses & Mémoires:Physique
Mots-clés :	Density Functional Theory (DFT) BaTiO₃ Structural properties Electronic properties Elastic properties Optical properties Pressure CASTEP Band gap
Index. décimale :	530 - Physique
Résumé :	This study aims to analyze the physical properties of the compound (BaTiO₃ Barium Titanate) using Density Functional Theory (DFT) and the PP-PW method within the CASTEP program. The research included the study of the structural, electronic, elastic, and optical properties of the compound under the influence of pressure, with a comparison of the results to the available theoretical and experimental data. The results showed that increasing pressure leads to a decrease in the lattice constant and cell volume, indicating the compressibility of the material. The elastic properties also showed a significant improvement in the compound's resistance to stress, with increases recorded in the elastic moduli such as C₁₁, C₁₂, and the bulk modulus B. From an electronic perspective, a slight increase in the energy gap was observed from 2.071 eV to 2.205 eV at 15 GPa, reflecting the effect of pressure on the band structure. As for the optical properties, there has been an improvement in the absorption coefficient, optical conductivity, and reflectivity, highlighting the potential use of BaTiO₃ in advanced electro-optical applications. These results confirm that the compound BaTiO₃ possesses multiple and distinctive properties under pressure, making it a promising candidate in the fields of electronics, solar cells, and sensors. They also support its consistency with previous literature, providing new insights into the material's behavior under harsh conditions.
Note de contenu :	Sommaire Table of contents......................................................................................................6 General Introduction : ...................................................................................... 12 Chapiter I: Theory and Numerical Calculations of DFT and PP-PW Methods I .1.Introduction ............................................................................................... 16 I.2. Schrödinger's equation .............................................................................. 16 I. 3. Born-Oppenheimer approach .................................................................. 17 I. 4. Hartree-Fock estimation........................................................................... 17 I. 5. Density functional theory (DFT) .............................................................. 18 I. 5. 1. Hohenberg and Kohn Theore .................................................................. 18 I. 5. 2. Kohn-Sham Equations ............................................................................. 19 I. 5. 3. The Exchange and Correlation Functional ............................................ 22 I.6 Pseudo-potential methods and plane waves .............................................. 25 I.6.1 Introduction ................................................................................................ 25 I.6.2 Bloch Theorem (the plane wave approach) ............................................... 26 I.6.3 Sampling of the first Brillouin zone ........................................................... 26 I.6.4 Ecut-off energy ............................................................................................ 27 I.7. CASTEP code............................................................................................. 28 Chapiter II:General Study of Perovskites and The Properties and Applications of BaTiO3 II.1 Introduction ............................................................................................... 33 II.2 Structure of perovskites: ........................................................................... 33 II.2.1. Simple perovskites .................................................................................... 35 II.2.2. Complex perovskites ................................................................................ 35 II.3 Stability conditions for ABO₃ perovskites................................................ 35 II.3.1 Tolerance factor......................................................................................... 35 II.3.2 Ionicity of bonds ........................................................................................ 36 II.4 Properties of perovskites ........................................................................... 37 II.4.1 Piezoelectricity ........................................................................................... 37 II.4.2 . Pyroelectricity .......................................................................................... 38 II.4.3. Ferroelectricity ......................................................................................... 39 II.5. Use of perovskites ..................................................................................... 42 II.6 General information on barium titanate .................................................. 43 II.6.1. definition ................................................................................................... 43 II.6.2. Phase transitions ....................................................................................... 44 II.6.3. BaTiO3 hysteresis cycle ............................................................................ 46 II.6.4. BaTiO₃ applications .................................................................................. 47 Chapter III: Structural, Electronic , elastic and optical properties of compound BaTiO3 III.1. Introduction: ........................................................................................... 51 III.2. Calculation details: ................................................................................. 51 III.3. Structural properties: ............................................................................. 51 III.4. Elastic properties of BaTiO3 compound: .............................................. 55 III.4.1. Calculation of elastic constants : ............................................................ 55 III.5. Electronic properties : ............................................................................ 59 III.5. 1. Electronic band structures: ................................................................... 60 III.5.2. Electron Charge Density : .................................................................... 62 III.5. 3. Density of States (DOS) and Partial Density of States (PDOS) : ....... 64 III. 6. Optical properties : ................................................................................ 66 III. 6. 1.Absorption coefficient : ......................................................................... 67 III. 6. 2.Optical conductivity :............................................................................. 69 III. 6. 3.Dielectric function :................................................................................ 70 III. 6. 4. Electronic Loss Function ...................................................................... 72 III. 6. 5. Reflectivity ............................................................................................. 73 III. 6. 6. Refractive Index .................................................................................... 74 General Conclusion : ........................................................................................... 79
Côte titre :	MAPH/0690

Investigation on the structural, elastic, electronic and optical properties of BaTiO₃: An ab initio study [document électronique] / Kawter Ben Amara, Auteur ; Amer Saoudi, Directeur de thèse . - [S.l.] : Setif:UFA, 2025 . - 1 vol (80 f.) ; 29 cm.
Langues : Anglais (eng)

Catégories :	Thèses & Mémoires:Physique
Mots-clés :	Density Functional Theory (DFT) BaTiO₃ Structural properties Electronic properties Elastic properties Optical properties Pressure CASTEP Band gap
Index. décimale :	530 - Physique
Résumé :	This study aims to analyze the physical properties of the compound (BaTiO₃ Barium Titanate) using Density Functional Theory (DFT) and the PP-PW method within the CASTEP program. The research included the study of the structural, electronic, elastic, and optical properties of the compound under the influence of pressure, with a comparison of the results to the available theoretical and experimental data. The results showed that increasing pressure leads to a decrease in the lattice constant and cell volume, indicating the compressibility of the material. The elastic properties also showed a significant improvement in the compound's resistance to stress, with increases recorded in the elastic moduli such as C₁₁, C₁₂, and the bulk modulus B. From an electronic perspective, a slight increase in the energy gap was observed from 2.071 eV to 2.205 eV at 15 GPa, reflecting the effect of pressure on the band structure. As for the optical properties, there has been an improvement in the absorption coefficient, optical conductivity, and reflectivity, highlighting the potential use of BaTiO₃ in advanced electro-optical applications. These results confirm that the compound BaTiO₃ possesses multiple and distinctive properties under pressure, making it a promising candidate in the fields of electronics, solar cells, and sensors. They also support its consistency with previous literature, providing new insights into the material's behavior under harsh conditions.
Note de contenu :	Sommaire Table of contents......................................................................................................6 General Introduction : ...................................................................................... 12 Chapiter I: Theory and Numerical Calculations of DFT and PP-PW Methods I .1.Introduction ............................................................................................... 16 I.2. Schrödinger's equation .............................................................................. 16 I. 3. Born-Oppenheimer approach .................................................................. 17 I. 4. Hartree-Fock estimation........................................................................... 17 I. 5. Density functional theory (DFT) .............................................................. 18 I. 5. 1. Hohenberg and Kohn Theore .................................................................. 18 I. 5. 2. Kohn-Sham Equations ............................................................................. 19 I. 5. 3. The Exchange and Correlation Functional ............................................ 22 I.6 Pseudo-potential methods and plane waves .............................................. 25 I.6.1 Introduction ................................................................................................ 25 I.6.2 Bloch Theorem (the plane wave approach) ............................................... 26 I.6.3 Sampling of the first Brillouin zone ........................................................... 26 I.6.4 Ecut-off energy ............................................................................................ 27 I.7. CASTEP code............................................................................................. 28 Chapiter II:General Study of Perovskites and The Properties and Applications of BaTiO3 II.1 Introduction ............................................................................................... 33 II.2 Structure of perovskites: ........................................................................... 33 II.2.1. Simple perovskites .................................................................................... 35 II.2.2. Complex perovskites ................................................................................ 35 II.3 Stability conditions for ABO₃ perovskites................................................ 35 II.3.1 Tolerance factor......................................................................................... 35 II.3.2 Ionicity of bonds ........................................................................................ 36 II.4 Properties of perovskites ........................................................................... 37 II.4.1 Piezoelectricity ........................................................................................... 37 II.4.2 . Pyroelectricity .......................................................................................... 38 II.4.3. Ferroelectricity ......................................................................................... 39 II.5. Use of perovskites ..................................................................................... 42 II.6 General information on barium titanate .................................................. 43 II.6.1. definition ................................................................................................... 43 II.6.2. Phase transitions ....................................................................................... 44 II.6.3. BaTiO3 hysteresis cycle ............................................................................ 46 II.6.4. BaTiO₃ applications .................................................................................. 47 Chapter III: Structural, Electronic , elastic and optical properties of compound BaTiO3 III.1. Introduction: ........................................................................................... 51 III.2. Calculation details: ................................................................................. 51 III.3. Structural properties: ............................................................................. 51 III.4. Elastic properties of BaTiO3 compound: .............................................. 55 III.4.1. Calculation of elastic constants : ............................................................ 55 III.5. Electronic properties : ............................................................................ 59 III.5. 1. Electronic band structures: ................................................................... 60 III.5.2. Electron Charge Density : .................................................................... 62 III.5. 3. Density of States (DOS) and Partial Density of States (PDOS) : ....... 64 III. 6. Optical properties : ................................................................................ 66 III. 6. 1.Absorption coefficient : ......................................................................... 67 III. 6. 2.Optical conductivity :............................................................................. 69 III. 6. 3.Dielectric function :................................................................................ 70 III. 6. 4. Electronic Loss Function ...................................................................... 72 III. 6. 5. Reflectivity ............................................................................................. 73 III. 6. 6. Refractive Index .................................................................................... 74 General Conclusion : ........................................................................................... 79
Côte titre :	MAPH/0690