| Titre : | Study of mechanical and physical properties Of thermoelectric materials for energy conversion. |
| Auteurs : | Maria Nor Elyakin Boumezrag, Auteur ; Said Lakel, Directeur de thèse ; Kenza Almi , 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.(161.p) / ill.couv.ill.en coul / 30cm |
| Langues: | Anglais |
| Langues originales: | Anglais |
| Mots-clés: | Alkali doped CuO, spin coating, solvent, structural properties, thermoelectric properties |
| Résumé : |
Study of mechanical and physical properties of thermoelectric materials for energy conversion. his study investigates the fabrication and characterization of CuO thin films on glass substrates using the spin coating technique. Key experimental parameters, including solvent type, annealing temperature, film thickness, and alkali metal (Li, Na, K) doping at concentrations of 3%, 6%, 9%, and 12%, were optimized to enhance the structural, optical, electrical, and thermoelectric properties of the films. X-ray diffraction (XRD) analysis confirmed the polycrystalline monoclinic structure of CuO, with variations in crystalline peaks and lattice structure influenced by different solvents. Isopropanol, 1-propanol, ethanol, and 2-methoxyethanol promoted growth along the c-axis (002 plane), whereas pentanol and methanol favored (111) plane growth. Isopropanol-based films exhibited the largest crystallite size and improved optical transmittance, while crystallinity improved with annealing up to 500°C. Optimized film deposition with nine layers resulted in an approximate thickness of 400 nm, leading to smaller crystallites with higher strain. Other hand, across all doping levels, the monoclinic phase was preserved. Sodium and potassium doping led to lattice compression, whereas lithium reduced lattice volume at higher concentrations. Optically, sodium and potassium doping enhanced transmittance, with potassium providing the best optical clarity at 6%, while lithium reduced transmittance and increased the band gap. Urbach energy increased in all doped films, indicating higher disorder, with potassium-doped films showing the least disorder at 6%. For the electrical properties, electrical conductivity was improved with sodium and potassium doping, peaking at 6%, with sodium achieving a conductivity of 5.93 × 10⁻² (Ω cm) ⁻¹ and potassium exhibiting the lowest resistivity. Lithium doping enhanced conductivity up to 6%, but further doping led to a decline. The best thermoelectric performance was observed in Li-doped CuO, which exhibited the highest power factor (9.776 × 10⁻¹⁰ W. m⁻¹.K⁻²). Additionally, the study of mechanical and elastic properties confirmed CuO's strong anisotropy and mechanical stability. These findings highlight the potential of doped CuO thin films for applications in optoelectronics, thermoelectric, and flexible electronics, demonstrating the ability to fine-tune their properties through controlled doping and processing techniques. |
| Sommaire : |
I.1. Introduction .................1 I.2. Cupric (II) oxide ......... 6 I.3. Properties of cupric oxide thin films ...................... 7 I.3.1. Structural properties .7 I.3.2. Electrical properties ................... 13 I.3.3. Optical properties ..17 I.3.4. Mechanical properties ............................ 19 I.4. CuO doping ............ 21 I.5. Applications of copper oxide .......................... 22 I.5.1. Gaz sensing ............. 22 I.5.2. Photo- catalysis ........24 I.5.3. Solar cells ................ 25 I.5.4. Thermoelectric application ................................... 27 Reference ........ 29 Chapter II : Experimental details and characterization methods II.1. Introduction ......... 42 II.2. Sol gel process ........ 42 II.3. Spin coating technique 45 II.4. CuO thin films preparation ...................... 49 II.5. Characterization methods ..................................... 52 II.5.1. Physico-chemical characterizations ...................... 52 II.5.1.1. Thin Film’s thickness Measurement ...................................................................... 52 II.5.1.2. X-ray diffraction (XRD) .............................................. 52 II.5.1.3. Scanning electron microscopy (SEM) ................................ 55 II.5.1.4. Energy-Dispersive Spectrometry (EDS) ........ 56 II.5.1.5. UV –Visible spectroscopy ............................... 57 II.5.2. Electrical characterization techniques: ............... 58 II.5.2.1. four probes method .......=.................................. 66 II.6 DFT characterization of mechanical properties …………………………………...….…63 Reference .................. 66 Chapter III : The solvent, number of layers and annealing temperature influence on .CuO thin films properties III.1. Solvent effect .......... 72 III.1.1. Introduction ....... 72 III.1.2. Result and discussions ........................... 73 III.1.2.2. Optical properties: ........................ 76 III.1.2.3. Electrical properties ........... 81 III.2. Thickness effect .................... 82 III.2.1. Introduction ....................... 82 III.2.2. Result and discussions .................. 82 III.2.2.1. Thin film’s thickness Measurement ......82 III.2.2.2. Structural properties.83 III.2.2.3. Optical properties .....86 III.2.2.4. Electrical properties ..................91 III.3. Annealing temperature effect..........93 III.3.1. Introduction .............93 III.3.2. Result and discussions 93 III.3.2.1. Structural properties: ......................93 III.3.2.2. Optical properties ...99 III.3.2.3. Electrical Characterization .................. 103 III.4. Conclusion................... 104 Reference ............................ 105 Chapter IV : Influence of alkali doping CuO thin films IV.1. Introduction ........... 109 IV.2. Results and discussion ............... 109 IV.2.1. Lithium doped Copper oxide ..................... 109 IV.2.1.1. Structural characterizations .......... 112 IV.2.1.2. Optical properties ................. 116 IV.2.1.3. Electrical properties ........... 117 IV.2.2. Sodium doped copper oxide .............................................. 117 IV.2.2.1. Structural characterizations ............. 117 IV.2.2.2. Optical properties .............................. 121 IV.2.2.3. Electrical properties ............................. 125 IV.2.3 Potassium doped copper oxide ........................... 126 IV.2.3.1. Structural characterizations ................. 126 IV.2.3.2. Morphological (SEM) and chemical composition (EDX) analysis ................... 129 IV.2.3.3. Optical properties .......................... 134 IV.2.3.4. Electrical properties ......................... 132 IV.2.4. Thermoelectric properties ............................................. 140 IV.2.4.1. Conductivity Type .................................. 140 IV.2.4.2. The Seebeck coefficient ....................................... 141 IV.2.4.3. The Power Factor (PF) ........................................ 142 IV.2.5. Elastic constants and mechanical properties ........................ 135 IV.2.5.2. Polycrystalline elastic constants ............................................................................... 145 IV.2.5.3 Anisotropy of elastic moduli ...................................... 148 IV.3. Conclusion: .............147 Reference .............. 156 General Conclusion and future work………………………………………………………161 |
| Type de document : | Thése doctorat |
| En ligne : | http://thesis.univ-biskra.dz/id/eprint/6850 |
Disponibilité (1)
| Cote | Support | Localisation | Statut |
|---|---|---|---|
| TPHY/150 | Théses de doctorat | bibliothèque sciences exactes | Consultable |
