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Alkaline/Alkaline-Earth Silicide and Germanides Alloys for Energy Applications

Mardi 21 novembre 2023 10:00 - Duree : 2 heures
Lieu : Amphithéâtre - CNRS Délégation Occitanie Est - 1919, route de Mende - 34090 Montpellier cedex 5

Orateur : Soutenance de Thèse de Doaa ALI (Univ. Montpellier & ILL)

Soutenance en anglais

ZOOM LINK : https://umontpellier-fr.zoom.us/j/96060169241

Abstract :

The primary objective of the research presented in this thesis focuses on the investigation and development of environmentally friendly alloys composed of alkaline and alkali-earth elements in combination with silicon and germanium, in the context of thermoelectric applications, and electrochemical studies, with relevance to battery applications. A drawback of the best-performing materials for these energy applications is their toxicity, scarcity, and/or costs of the chemical elements they are synthesized from. For this reason, alkaline and alkali-earth silicides have attracted high interest as they are made of abundant, cheap, and non-toxic elements. Among their many compounds, this study has focused on investigating semiconducting hexagonal Ca3Si4, and rhombohedral Ca14Si19, in the context of thermoelectricity. Both Ca3Si4 and Ca14Si19 compounds possess complex structures with narrow energy bandgaps, rendering them well-suited for achieving low thermal conductivities and high power factors, ultimately resulting in a large dimensionless figure of merit (ZT). In ab initio calculations, another silicide compound, α-SrSi2, was predicted to exhibit a semiconducting structure with a narrow bandgap. Thus making the three compounds promising candidates for investigation as thermoelectric materials (TEMs). Furthermore, In the context of electrochemical studies, the goal is to investigate the mobility of Na within Ge through electrochemistry experiments on NaGe compound. Additionally, this study extends to high-pressure high-temperature experiments to synthesize NaxSiy compounds, which hold promise to be studied for energy-related applications in the future. To gain a comprehensive understanding of the macroscopic and microscopic physical properties of the different studied compounds, a wide array of measurement techniques are employed in combination with density functional theory (DFT) calculations. These measurements encompass diverse methods, including neutron and x-ray diffraction for investigating the structural properties of the compounds. Additionally, the inelastic neutron spectroscopy is used to probe the lattice vibrations responsible for heat transport in Ca3Si4, Ca14Si19, α-SrSi2, and NaGe compounds. Furthermore, a new synthesis reactive spark plasma sintering technique for synthesizing Ca14Si19 in a few minutes is introduced beside the conventional annealing method. This study also reports thermoelectric measurements to assess the potential of materials such as Ca3Si4 and Ca14Si19 for thermoelectric applications.

Contact : tellier@ill.fr

Discipline évènement : (Physique)
Entité organisatrice : (ILL)
Nature évènement : (Soutenance de thèse)

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