Inass EL HAJJ: Molten LiCl-KCl eutectic mixture: a novel medium for the intercalation of alkaline-earth and lanthanide metals into graphite

Abstract:
Graphite intercalation compounds (GICs) are 2D materials that are subjected to numerous theoretical and experimental studies. In particular, these compounds have attracted a lot of attention from the scientific community regarding their superconducting properties at low temperature. Many GICs reported in the literature have been synthesized by changing the nature of the intercalated species. The first ones, resulting from an intercalation reaction between graphite and alkali metals, were obtained by direct action of metallic vapor on graphite. Since, a great deal of research has been carried out on graphite-electron donor systems, mainly those involving alkaline earth metals and lanthanides. Recently, researches have been carried out using a novel synthesis route involving eutectic medium LiCl-KCl as intermediate for intercalating various metals (strontium, barium, ytterbium and samarium) into graphite. Within this framework, the compounds prepared in this work have been characterized by X-ray diffraction, nuclear microprobe and Raman spectroscopy in order to carry out structural, chemical and physical properties studies. Differential scanning calorimetry has also been used to better understand the behavior of metals in molten salts.
Therefore, after a bibliographic presentation of the state of the art, the first part of this work entails in describing the results obtained concerning first stage binary compounds SrC6 and BaC6. Attempts to synthesize binary compounds YbC6 and SmC6 are also reported.
The second part of this work focuses on new phases synthesized from graphite Ba/LiCl KCl and graphite-Sr/LiCl-KCl systems. In each case, two compounds noted α and β could be identified and characterized. A reaction mechanism elucidating the formation of these GICs could be proposed. Calorimetric studies are carried out in order to inspect the behavior of metals towards molten salts and to further understand the chemical phenomena leading to graphite intercalation compounds in this medium .

Keywords:
intercalation – graphite – alkaline earth – lanthanides – molten salts – XRD – nuclear microprobe – Raman – DSC

Composition of the jury:
> Reporters:
- Marc DUBOIS, Professeur, ICCF, Université Clermont Auvergne
- Guillaume ROGEZ, Directeur de recherche CNRS, IPCMS, Université de Strasbourg
> Examiners:
- Nicolas EMERY, Chargé de recherche CNRS, ICMPE, Université Paris‑Est Créteil
- Claire HEROLD, Directrice de recherche CNRS, IJL, Université de Lorraine
> Direction of thesis:
- Sébastien CAHEN, Directeur de thèse, Maître de conférences, IJL, Université de Lorraine
- Lucie SPEYER, Co-directrice de thèse, Maître de conférences, IJL, Université de Lorraine