ED Sciences Chimiques
Synthesis, characterization and shaping of nanoparticles based on SrTiO3 as EHT anode materials for the oxidative coupling of methane
by Arnaud DANDRE (ICMCB - Institut de Chimie de la Matière Condensée de Bordeaux)
The defense will take place at 14h00 - Amphithéatre Institut de Chimie de la Matière Condensée de Bordeaux (ICMCB) 87 Avenue du Dr Albert Schweitzer, 33600 Pessac
in front of the jury composed of
- Cyril AYMONIER - Directeur de recherche - CNRS-ICMCB - Directeur de these
- Maryline GUILLOUX-VIRY - Professeure - Université de Rennes - Rapporteur
- Bo Brummerstedt IVERSEN - Professeur - Aarhus University - Rapporteur
- Akira YOKO - Professeur associé - Tohoku University - Examinateur
- Roger DE-SOUZA - Professeur - Aachen University - Examinateur
- Jean-Marc BASSAT - Directeur de recherche - CNRS-ICMCB - CoDirecteur de these
- Mario MAGLIONE - Directeur de recherche - CNRS-ICMCB - Examinateur
- Gilles PHILIPPOT - Maître de conférences - Université de Bordeaux-ICMCB - Examinateur
Strontium titanate (SrTiO3) is a material of great interest due to its remarkable electrical, optical, and catalytic properties, as well as its chemical stability. Its perovskite-type crystal structure, which allows for various dopings to easily adjust its properties, is central to its appeal. Among the synthesis methods for doped and undoped SrTiO3, the supercritical fluid route presents an intriguing alternative. Indeed, in the field of materials science, the supercritical fluid route has revolutionized the synthesis of nanoparticles, thin films, and porous materials. This method not only enables the creation of materials that cannot be obtained through conventional approaches but also achieves a uniform particle size distribution, high purity, and improved crystallinity which is a key factor for optimizing material performance. Strontium titanate allows doping at both A-site (strontium) and B-site (titanium). The most common doping involves rare earth elements at the strontium site or transition metals at the titanium site. The goal of doping is to enhance specific properties for photocatalysis, optics, or dielectric and electronic characteristics. Various synthesis processes have yielded doped strontium titanate compositions, ranging from solid-state reactions to more advanced methods like sol-gel or hydrothermal synthesis. However, the synthesis of doped strontium titanate via the supercritical fluid route has not been reported, except for the complete solid solution between barium titanate and strontium titanate. In this thesis work, the synthesis of strontium titanate via the continuous-flow supercritical solvothermal method has been successfully achieved using alkoxide and acetylacetonate precursors. Once the synthesis was validated, compositions with dopants were produced by substituting strontium with rare earth elements such as praseodymium and titanium with transition metals like niobium, demonstrating the flexibility of this method to obtain n- or p-doped materials with precise atomic doping rates ranging from a maximum substitution rate of 10 at.% down to 1 at.%, thereby improving electronic properties. Additionally, these electronic properties were characterized to assess the impact of doping. The electronic conduction properties were then determined, revealing that for certain compositions, the conductivity was 1,000 times greater than that of the bare strontium titanate. This increased conductivity makes the material viable for electrode applications in various electrochemical devices, such as electrolyzer. These electrodes were developed by formulating nanoparticles into ink and depositing them onto a substrate via screen printing. The final envisioned application for this material is as an anode in a high-temperature electrolyzer. Due to its conductive properties and nanoscale size, this material could facilitate the catalytic oxidative coupling of methane and promote the conversion of methane to ethylene.
ED Sciences de la Vie et de la Santé
Exploring prefrontal cortex dysfunction in the Fmr1KO mouse models of autism and fragile X syndrome
by Maria José GUEIDAO COSTA (Neurocentre Magendie)
The defense will take place at 15h00 - SeminarroomatBBS 146 Rue Léo Saignat 33077 Bordeaux Cedex
in front of the jury composed of
- Cristina MIGUELEZ PALOMO - Associate Professor - Université du Pays Basque - Examinateur
- Graziella DI CRISTO - Professeure des universités - CHU Sainte-Justine - Examinateur
- Ingrid BUREAU - Chargée de recherche - Institut de Neurobiologie de la Méditerranée Inmed U1249 - Rapporteur
- Raül ANDERO GALI - Professeur des universités - Institute of Neuroscience – Autonomous University of Barcelona - Rapporteur
- Christophe MULLE - Professeur des universités - IINS - Centre Broca Nouvelle-Aquitaine - Examinateur
Neurodevelopmental disorders are conditions affecting nervous system development, leading to a range of clinical features, including difficulties with cognitive function, adaptive behaviour, or the processing of sensory information. Fragile X syndrome, an ‘archetypal' neurodevelopmental disorder, with extensive overlap with other conditions such as autism and attention deficit and hyperactivity disorder, is modelled by the Fmr1KO mouse. Here, we probed the role of the prefrontal cortex alterations in the complex pathophysiology of this model. To do this, we first developed a custom-made operant task testing auditory discrimination and sensory filtering in freely moving animals. The task was designed to optimize engagement and self-directed behaviour, while maximizing both ethological and translational considerations. The task requires extensive training and is sensitive to the quality of the acoustic stimuli. As a complementary approach, we employed trace fear conditioning, which permits insight into sustained attention, working memory, emotional regulation. We combined this task with 1-photon based imaging of Ca2+ activity using a head-mounted miniaturized microscope (miniscope). This approach allows the correlation of neuronal activity at cellular resolution with behavioural phenotypes allowing us to access physiological biomarkers of altered prefrontal cortex function. Using this approach, we have been able to identify event-specific signatures related to prefrontal function in the Fmr1KO model. Future experiments will explore whether these physiological changes are unique to the Fmr1KO model and to the task, or conserved in other genetic mouse models with known impairments in attention and sensory information processing.
ED Sciences Physiques et de l'Ingénieur
Development and data analysis of the R2D2 prototypes, aiming at the optimisation of a high pressure xenon gas TPC for neutrinoless double beta decay search
by Pierre CHARPENTIER (Laboratoire de Physique des 2 Infinis de Bordeaux)
The defense will take place at 14h00 - Salle Marie Curie LP2i Bordeaux, 19 chemin du Solarium 33170 Bordeaux
in front of the jury composed of
- Anselmo MEREGAGLIA - Directeur de recherche - Université de Bordeaux - Directeur de these
- Davide FRANCO - Directeur de recherche - Université de Paris Cité - Rapporteur
- Margherita BUIZZA AVANZINI - Chargée de recherche - Institut Polytechnique de Paris - Rapporteur
- Jérôme GIOVINAZZO - Directeur de recherche - Université de Bordeaux - Examinateur
- Pascal LAUTRIDOU - Directeur de recherche - Institut Mines-Télécom - Examinateur
While the Standard Model (SM) of particle physics assumes a massless Dirac neutrino, discoveries of the late 20th century have contradicted this hypothesis. Some modern extensions of the SM assume a so-called Majorana neutrino, where neutrino and antineutrino are no longer two distinct particles, but a single fundamental particle. Observation of the neutrinoless double-beta decay process would make it possible to confirm the Majorana nature of the neutrino, but this remains a challenge for experimental physics. The work carried out as part of this thesis is part of the research for the observation of this process by the R2D2 collaboration, which is currently in the research and development (R&D) phase. The main objective of the R&D is to study the energy resolution capacities of high-pressure xenon time-projection chambers (HPXe-TPC). The ultimate goal of R&D is to demonstrate the feasibility of a detector with energy resolution of 1% FWHM at 2.46 MeV using high-pressure xenon. To meet this objective, four prototypes of the detector, designed by the R2D2 collaboration, were studied at the Laboratoire de Physique des 2 infinis in Bordeaux. Two proportional counter geometries, spherical (SPC) and cylindrical (CPC), were tested under various experimental conditions and two gaseous detection regions. Work carried out on the gas purification and recirculation circuits has led to measurements at pressures up to 10 bar in argon and 6 bar in xenon. These measurements enabled us to obtain resolution measurements at the 1% FWHM level for alpha resulting from the decay of 210Po of energy 5.3 MeV in argon and in xenon. The advantages of CPCs over SPCs have convinced the R2D2 collaboration to continue developing this technology for future detector deployment.