| Titre : | Synthesis and study of the dielectric properties of a doped NBT type material |
| Auteurs : | rahima Rahal, Auteur ; Malika Abba , Directeur de thèse ; Zelikha Necira, Directeur de thèse |
| Type de document : | Thése doctorat |
| Editeur : | Biskra [Algérie] : Faculté des Sciences Exactes et des Sciences de la Nature et de la Vie, Université Mohamed Khider, 2025 |
| Format : | 1VOL.(128p) / ill.couv.ill.en coul / 30cm |
| Langues: | Anglais |
| Langues originales: | Anglais |
| Mots-clés: | Rare earths .Dielectric .MB. Dye. Photocatalytic. Sunlight irradiation. |
| Résumé : |
The present study reports the fabrication of NBT-type ceramic materials with the general formula (Na0.5Bi0.5) 0.94 R 0.04Ti 0.95 (Ni0.2 Fe0.2 Sb0.6) 0.05O3 (abbreviated as NBT-RNFS), where R denotes the dopant elements La, Nd, Gd, and Y. The ceramics were synthesized via the conventional solidstate reaction method. The main objective of this study was to investigate the effect of rare earth doping on the dielectric and photocatalytic properties of novel NBT-based ceramic materials. The NBT-RNFS samples were successfully synthesized at 1150°C. Undoped NBT-NFS samples had a single rhombohedral phase, while rare earth-doped NBT-NFS samples showed a rhombohedral phase along with a pyrochlore phase. Rietveld refinement of the XRD data showed a slight shrinkage of the unit cell volume with the substitution of rare earth elements, attributed to their relatively lower ionic radii compared to the host ions. Optical bandgap analysis revealed that the fabricated perovskite samples exhibited semiconducting behavior, with measured bandgap values ranging from 2.61 to 2.80 eV. The La-doped NBT-RNFS system exhibited an impressive 83% photocatalytic dye degradation rate, substantially outperforming the 23% dye removal efficiency of the undoped material. Similarly, the Nd-doped (62% dye removal) and Y-doped (66% dye removal) NBT-RNFS ceramics also displayed enhanced photocatalytic activities under broadband solar light exposure. The La-doped NBT-RNFS composition demonstrated an exceptionally high dielectric constant (εr) of 1151.87, while the Nd-doped NBT-RNFS exhibited a dielectric constant of 1122.31. These values significantly exceeded the dielectric constant of 951.02 obtained for the undoped NBT-NFS ceramic. |
| Sommaire : |
List of symbols and abbreviations Liste of Figures Liste of Tables General Introduction .............................................................................................................. 1 References bibliographiques ...................................................................................................... 4 Chapter I: TECHNICAL BACKGROUND I.Introduction……………………………………………………………………...……………6 I.1 Part A: Basics of photocatalysis ........................................................................................... 6 I.1.1 Photocatalysis ................................................................................................................. 6 I.1.2 The principle of photocatalysis ...................................................................................... 7 I.1.3 Photocatalytic reactions mechanism .............................................................................. 8 I.1.4 Perovskite materials in photocatalysis ......................................................................... 10 I.1.5 Diverse applications of photocatalysis ......................................................................... 12 I.2 Part B: Basics of ferroelectrics ........................................................................................... 12 I.2.1 Dielectric materials ...................................................................................................... 12 I.2.2 Dielectric properties ..................................................................................................... 12 I.2.3 Dielectric constant ........................................................................................................ 14 I.2.4 Dielectric losses ............................................................................................................ 15 I.2.5 Quality Factor ............................................................................................................... 16 I.2.6 Curie-Weiss behavior ................................................................................................... 16 I.2.7 Polarization mechanisms .............................................................................................. 16 I.2.7.1 Electronic polarization Pelec ................................................................................... 17 I.2.7.2 Ionic polarization (Atoms) Pions ............................................................................. 17 I.2.7.3 Orientation or dipolar polarization Por ................................................................... 17 I.2.7.4 Space Charge Polarization Psc ............................................................................... 18 I.2.8 Variation of dielectric constant with frequency ........................................................... 18 I.2.9 Ferroelectric materials .................................................................................................. 19 I.2.9.1 Definition ............................................................................................................... 19 I.2.9.2 Ferroelectric Hysteresis ......................................................................................... 20 I.2.9.3. Ferroelectric domains: .......................................................................................... 22 I.2.9.4 Polar nanoregions .................................................................................................. 23 I.2.9.5.Classification of symmetry classes ........................................................................ 24 I.2.10 Piezoelectricity ............................................................................................................... I.2.10 Pyroelectricity ............................................................................................................ 25 I.2.11 Utilization of ferroelectric materials .......................................................................... 26 I.2.12 Na0.5Bi0.5TiO3-Based ceramics (NBT) ....................................................................... 26 I.2.12.1 Structural properties ............................................................................................ 26 I.2.12.2 Phase formation ................................................................................................... 27 I.2.12.3 Ion Substitution .................................................................................................... 27 Conclusion ................................................................................................................................ 29 Biblogrqphic references ........................................................................................................... 30 Chapter II:Synthesis & Characterization Techniques II.1.Introduction ...................................................................................................................... 37 II.2 Choice of materials and dopants: ....................................................................................... 37 II.3 Experimental Details ......................................................................................................... 38 II.4 Solid State Reaction Method ............................................................................................. 38 II.5 Characterization technique ................................................................................................ 39 II.5.1Thermal analysis (DTA)/TGA: .................................................................................... 39 II.5.2 Density measurements ................................................................................................ 41 II.5.2. 1 Archimedes’ Density ........................................................................................... 41 II.5. 2.2 Theoretical Density ............................................................................................. 42 II.5.2. 3 Relative Density .................................................................................................. 42 II.5.3 XRD Analyses ............................................................................................................ 43 II.5.4 .The Rietveld Refinement Method .............................................................................. 44 II.5.5 Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS/EDX) .............................................................................................................................................. 45 II.5.6 ATR-FTIR spectroscopy ............................................................................................. 46 II.5.7 Raman Spectroscopy ................................................................................................... 48 II. 5.8 UV –Visible spectroscopy ......................................................................................... 50 II.5.9 Classification of Adsorption Isotherms ...................................................................... 51 II.5. 10 The BET technique .................................................................................................. 52 II.5.11 BJH method .............................................................................................................. 53 II.5.12 t-plot model (surface area, micropore and mesopore volume) ................................. 53 II.5.13 Dielectric spectroscopy ............................................................................................. 54 Conclusion ................................................................................................................................ 57 Biblogrqphic references ........................................................................................................... 58 Chapter III: Study of the Reaction Sequences and Structural-Microstructural Properties of the Novel Na0.5Bi0.5 Ti0.95 (Ni0.2Fe0.2Sb0.6) 0.05O3 Solid Solution Introduction: ............................................................................................................................. 62 Part A: The Study of reaction sequences for the formation of a novel solid solution: Na0.5Bi0.5Ti0.95 (Ni0.2Fe0.2Sb0.6)0.05O3 ........................................................................................ 62 III 1.1. Previous works: ........................................................................................................ 62 III 1.2 Experimental part: ..................................................................................................... 63 III 1.3 NBT-NFS samples at different sintering temperatures: ............................................ 64 III 1.5. Phase analysis of raw materials: ............................................................................... 66 III 1.6 XRD outcomes: ......................................................................................................... 68 Part B: Structural and microstructural properties of the novel Na 0.5Bi 0.5 R0.04Ti 0.95 (Ni 0.2 Fe 0.2Sb 0.6)0.05O3 (R = La, Nd, Gd, Y) solid solution. ................................................................... 73 III 2.1 Phase identification .................................................................................................... 73 III 2.2.Evolution of lattice parameters .................................................................................. 76 III 2.3. Influence of the rare earth element on interatomic distances in NBT-RNFS samples.. .............................................................................................................................................. 77 III 2.4. Charge density .......................................................................................................... 79 III 2.5. The Goldschmidt Factor ........................................................................................... 80 III 2.6 Density (g/cm3) .......................................................................................................... 81 III 2.7. Microstructural analysis ........................................................................................... 82 III 2.8 Energy dispersive spectrometric analysis EDS ......................................................... 84 III 2.9. Fourier Transform Infrared spectroscopy (FTIR) .................................................... 86 III 2.10. Raman spectroscopy analysis: ................................................................................ 87 Conclusion ............................................................................................................................ 91 Biblogrqphic references ........................................................................................................... 92 Chapter IV:Photocatalytic and Dielectric Performance of Novel Rare-Earth Doped NBTRNFS Ceramic Materials INTRODUCTION .................................................................................................................... 98 Part A: Characterization and Evaluation of Photocatalytic Performance of Novel Ceramic NBTRNFS ........................................................................................................................................ 98 IV.1.1 Optical analysis ......................................................................................................... 98 IV.1.2 BET analysis.............................................................................................................. 99 IV.1.3 BJH Method (Pore size distribution) ....................................................................... 101 IV.1.4 T-plot ....................................................................................................................... 103 IV.1.5 Photocatalytic activity ............................................................................................. 105 IV.1.6 Photocatalytic mechanism ....................................................................................... 108 IV.1.7 Kinetic studies ......................................................................................................... 109 IV.2 Part B: Effect of rare-earth elements doping (R = Gd, La, Y, and Nd) on the dielectric properties of NBT-NFS ceramics. .......................................................................................... 112 IV.2.1 Dielectric constant ...........................................................................................112 IV.2.2 Dielectric loss (tanδ) ................................................................................................ 114 IV.2.3. Exploring the impact of rare earth elements on the dielectric properties of NBT-NFS ceramics: ............................................................................................................................. 116 IV.2.4 The effect of frequency ........................................................................................... 118 IV.2.5.The diffusivity parameter (γ) ................................................................................... 119 IV.2.6 Curie-Weiss Behavior ............................................................................................. 121 IV.2.7 Conductivity studies ................................................................................................ 123 Conclusion .......................................................................................................................... 124 Biblogrqphic references ......................................................................................................... 125 Conclusion general ................................................................................................................. 128 |
| Type de document : | Thése doctorat |
Disponibilité (1)
| Cote | Support | Localisation | Statut |
|---|---|---|---|
| TCH/126 | Théses de doctorat | bibliothèque sciences exactes | Consultable |
