Results of this research are available online in two published papers. / The main focus of this research was to synthesize and then to characterize the potential high-performance thermoelectric materials. In this regard, we have prepared a series of pure RECuSe2 (with RE = Pr, Sm, Gd, Dy and Er) and RECuTe2 (with RE = Er, Dy and Gd) and analyzed their crystal structure, electronic and physical properties. We used powder and single crystal X-ray diffraction techniques to analyze their crystal structures and employed energy dispersive X-ray spectrometry (EDS) to verify their chemical compositions. The temperature stability of the synthesized samples was examined by differential thermal and gravimetrical analysis. The high-purity consolidated pellets were prepared for physical properties measurements. We analyzed the relationship between their crystal structures and pertinent electronic properties through the LMTO calculations. The RECuSe2 phases adopt two structures, monoclinic and trigonal. The monoclinic structure (P21/c, z = 4) is observed for lighter rare earths (RE = Pr, Sm and Gd) and Cu-disordered trigonal structure for heavier rare earths (P m1, z = 1, RE = Dy and Er). The resistivity and Seebeck coefficient measurements indicate that the studied selenides are p-type semiconductors with relatively small activation energies (0.045-0.12 eV). However, their electrical resistivities are too high (0.49-220 Ohmcm at room temperature) to make them competitive thermoelectric materials. Electronic structure calculations indicate presence of a band gap in the RECuSe2 phases. The synthesized RECuTe2 phases (RE = Er, Dy and Gd) adopt a monoclinic-distorted variant (C2/m, z = 2) of the trigonal structure (P m1, Z= 1) observed for the RECuSe2 (with RE = Dy, Er). While such disorder may be beneficial for lowering their thermal conductivity, large values of electrical resistivity (0.02-0.87 Ohmcm at room temperature) make these phases unsuitable for practical applications. Comparing to the corresponding semiconducting selenides, the tellurides have lower resistivities, and display a metallic type resistivity. Such behavior stems from the closure of band gaps, which is verified by the electronic structures calculations. Structurally the RECuTe2 phases (with RE = Er, Dy and Gd) are similar to RECuSe2 with the P m1 structure. The monoclinic distortion in RECuTe2 is driven by Cu displacement inside the larger tetrahedral voids in the hexagonal close packing of the Te atoms. Most likely, Cu shifts to one side of the Te tetrahedra to optimize the Cu-Te interactions. / Thesis / Candidate in Philosophy

En vue de la réduction des problèmes engendrés par les phénomènes de retrait-gonflement des sols dans la dépression de la Lama au Sud du Bénin, nous avons entrepris des recherches dans le but de maîtriser le comportement de ces sols. Six échantillons de sols fins dont quatre argileux de cette région ont été prélevés. Différents essais ont été réalisés : une caractérisation macroscopique concernant les propriétés mécaniques et géotechniques et les essais microscopiques prenant en compte les analyses chimiques, thermiques, minéralogiques et microstructurales. Les sols étudiés sont constitués de différents minéraux argileux. Celle à structure fibreuse est à l'origine d’un comportement macroscopique particulier décelé par l’essai de gonflement libre. Les essais ont confirmé le fort potentiel de gonflement et de retrait de certains sols qui sont donc à l'origine des fortes dégradations rencontrées.Les résultats montrent que les sols traités se distinguent par les performances mécaniques acquises et peuvent être utilisés à différents niveaux de la chaussée selon leur teneur en liant.Les différentes méthodes utilisées ont révélé des facettes particulières de l'étude de traitement des sols fins. Principalement, nous avons noté que les informations apportées par les observations au Microscope Electronique à Balayage, les analyses thermiques et les analyses de Diffraction aux Rayons X ont permis de compléter l’analyse des résultats géotechniques. En somme, les méthodes de caractérisation géotechnique permettent d’avoir une idée générale du potentiel de gonflement, mais pour les études d’envergure, la réalisation d’études microscopiques est primordiale. / To help reduce the problems caused by phenomena due to the shrink-swell soil in the depression of the Lama in southern Benin, we have undertaken research in order to control the behavior of these soils. Six soil samples, including four clay from this area were taken. Different types of tests were performed: a macroscopic characterization concerning mainly mechanical and geotechnical properties and microscopic tests taking into account the chemical, thermal, microstructural and mineralogical analysis. The soils studied consist of different clay minerals. The fibrous structure is at the origin of a particular macroscopic behavior detected by the free swell test. The tests confirmed the potential for swelling and shrinking of some soils that are causing heavy damage.Three soils treated with different contents at Binder Hydraulic Road, were subjected to several tests. The results show that these soils are distinguished by the acquired mechanical performance and may be used at different levels of the floor according to binder content.Also, the different methods revealed specific facets of fine soil treatment study. Mainly, we noted that the information provided by the observations scanning electron microscope, thermal analysis and the analysis of diffraction X-Ray are very important and helped complete the analysis of geotechnical results for soil treatment. In sum, geotechnical characterization methods used to get a general idea of the swelling potential, but for large-scale studies, conducting microscopic studies is paramount.