Solid State Chemistry and Materials (CSM) team

Abstract
The work presented in this Ph.D. thesis focuses on the synthesis, structural analysis, properties characterization, and investigation of the temperature-dependent behavior of complex sulfides. The first part of this research has been devoted to the exploration of new phases in the Cr-Sn-S ternary diagram, specifically the Cr2Sn3S7 and SnCr2S4 phases, which exhibit complex crystallographic structures with multiple sublattices, that significantly contribute to their low lattice thermal conductivity. A multi-technique crystallographic approach to the Cr2Sn3S7 phase revealed two weakly bound sub-lattices, attributed to the presence of Sn2+ in the structure. The latter is responsible for the low thermal conductivity of the phase, as confirmed by both experimental and theoretical studies. For the SnCr2S4 phase, its low thermal conductivity can be explained by the incommensurate nature of its structure, as investigated using 3D electron diffraction combined with diffuse scattering simulations. The second part of this work focused on the study of the temperature-dependent behavior of the Cu26V2Sn6S32 phase, reported as a promising thermoelectric material. Synchrotron X-ray diffraction confirmed the absence of exsolution phenomena in samples prepared by mechanosynthesis, regardless of the densification process used. Finally, the formation mechanisms of Cr2Sn3S7, SnCr2S4, Cu26V2Sn6S32 and Cu26Ti2Sb6S32 during sealed tube synthesis are investigated using in situ neutron powder diffraction.

Jury

• Laurence CROGUENNEC, Directice de Recherche, Institut de Chimie de la Matiere Condensee de Bordeaux / Rapportrice

• David BERARDAN, Maître de conférence, Université Paris Sud / Rapporteur

• Catherine DEJOIE, Scientifique de ligne, European Synchrotron Radiation Facility / Examinatrice

• Emmanuel GUILMEAU, Directeur de recherche CNRS, ENSICAEN / Examinateur

• Stéphane JOBIC, Directeur de recherche CNRS, Institut des Matériaux Jean Rouxel de Nantes / Examinateur

• Mathieu PASTUREL, Directeur de Recherche, CNRS, Institut des Sciences Chimiques de Rennes / Directeur de thèse

• Carmelo PRESTIPINO, Chargé de Recherche, CNRS, ENSICAEN / Co-Directeur de thèse

• Pierric LEMOINE, Professeur, Université de Lorraine / Encadrant

Contact
Mathieu Pasturel - mathieu.pasturel@univ-rennes.fr