Thomas STEPHANT PhD defense

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Uranium sulfides: a crystal-chemical study by X-ray spectroscopy and an in-depth investigation of their physical properties
Uranium sulfides: a crystal-chemical study by X-ray spectroscopy and an in-depth investigation of their physical properties

Solid State Chemistry and Materials (CSM) team

Abstract
This work presents an in-depth investigation of binary and ternary uranium sulfides and their physical properties. High-energy-resolution X-ray spectroscopies (HERFD-XANES, RXES, RIXS) were used to determine uranium oxidation states, revealing predominantly U4+ together with compositions exhibiting mixed U3+/U4+.The measurements also confirm the greater covalency of U-S relative to U-O bonds. The study includes the ternary families U8TMS17, An2FeS5, UTMS3 et UnCu2S3n+1 (n = 3, 6)(TM = Sc - Ni et Ba; An = Th et U), in which TM3+ in several cases stabilizes mixed U3+/U4+ states. Bulk densification by spark-plasma sintering (SPS) yielded samples suitable for, in several cases for the first time, heat capacity and electrical resistivity measurements, together with complementary magnetic characterization. The compounds display a range of magnetic responses from Curie–Weiss paramagnetism to complex cooperative or ferrimagnetic ordering.

Jury

  • Jan Pieter Glatzel, Scientifique de ligne, ESRF, Grenoble / Reporter

  • António Gonçalves, Directeur de recherche, C²TN, Lisbonne, Portugal / Reporter

  • Sylvie Daviero-Minaud, Professeure, UCCS, Université de Lille, Lille / Examiner

  • Guillaume Morin, Directeur de recherche, CNRS, IMPMC, Paris / Examiner

  • Myrtille O.J.Y. Hunault, Scientifique de ligne, SOLEIL, Saint-Aubin / PhD Co-supervisor

  • Carmelo Prestipino, Chargé de recherche, CNRS, CRISMAT, Caen / PhD Co-supervisor

  • Mathieu Pasturel, Directeur de recherche, CNRS, ISCR, Rennes / PhD Supervisor

Contacts