Mathieu Chevereau PhD defense

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Glasses and Ceramics (V&C) team Abstract The work reported in this thesis manuscript focuses on the synthesis and the characterization of new infrared transparent ceramics. Gallium (III) selenide (Ga2Se3) powder was synthesized using sealed-tube method, and then sintered by Spark Plasma Sintering (SPS), to make dense and pore-free ceramics. Sintered ceramics exhibit a 100 % densification rate, and are transparent from 4,5 to 16,5 μm. However, absorption bands remain on the transmission spectra, which origins are discussed. The use of another synthesis technique (mechanosynthesis) also allowed the obtention of Ga2Se3 powder, and its sintering process is described. The sulphide glass KSb5S8 was chosen to elaborate transparent ceramics by complete crystallization of the glass. With a monoclinic structure, this crystalline phase exhibits a high birefringence. Its crystallization was therefore studied in order to determine the heat treatment conditions required to maintain a nanometer-scale grain size. KSb5S8 ceramics were obtained, but lacked transparency due to the presence of scattering centers. By slightly modifying the glass composition to KSb4,61S7,86, crystalline samples kept much of the transmission of the original glass. KSb4,61S7,86 ceramics are transparent from 4 to 13 μm, show no porosity, and are the first non-oxide transparent ceramics obtained by complete crystallization of glass. Jury Gaëlle DELAIZIR - Professor - IRCER, Université de Limoges / Reviewer Sylvain MARINEL - Professor - CRISMAT, Université de Caen Normandie / Reviewer Isabelle MONOT-LAFFEZ - Professor - GREMAN, Université de Tours / Examiner Cécile GENEVOIS - CNRS Research engineer - CEMHTI, Université d’Orléans / Examiner Sébastien CHENU - Associate professor - ISCR, Université de Rennes / PhD Director Louisiane VERGER \- CNRS Research fellow - ISCR, Université de Rennes / PhD Co-director Contacts Mathieu Chevereau, mathieu.chevereau@laposte.net Sébastien Chenu, sebastien.chenu@univ-rennes.fr