Understanding microstructural changes during heat treatment of iron-rich SmCo magnets
The magnetic properties of SmCo magnets (remanence and coercivity) are linked to their microstructure. The final microstructure develops after sintering during homogenization and ageing heat treatments. The optimum temperature and/or duration of these treatments depend on the magnet’s composition. One of the major areas of development for commercial Sm2Co17 magnets is to achieve both high magnetic performance and a reduction in critical materials (notably cobalt). This is achieved by substituting part of the Co with Fe, which also helps to reduce raw material costs. However, the literature shows that when the Fe content exceeds 20% by weight, the coercivity of the magnets is diminished.
The aim of the thesis will be to understand the role and sensitivity of the process parameters that govern the evolution of the microstructure within Fe-rich Sm2Co17 magnets and the resulting properties. These developments will be monitored through various characterization techniques (chemical analyses, magnetic measurements, SEM and TEM observations, etc.) carried out on samples taken at different stages of the process. The aim is to systematically monitor (for the first time for this type of magnet) the structural transformations (chemical segregation, changes in Sm content, presence of defects, oxygen contamination, etc.) that occur from the synthesis of the alloy through to the final magnet. These characterizations should lead to a description of the mechanisms underlying the formation of the expected microstructure. These mechanisms are activated during the various heat treatments, but the influence of the metallurgical and chemical state (for example, defect density and chemical inhomogeneity) inherited from previous stages of the process is still poorly understood and will need to be clarified.
Growth of FAPbBr3 by CSS for X-ray detection
Lead halide perovskites, and particularly hybrid organic-inorganic materials based on formamidinium, possess exceptional optoelectronic properties that have been intensively exploited for photovoltaic (PV) applications. Within this family of materials, FAPbBr3 is also particularly promising for X-ray detection in medical applications. However, this technology requires the ability to deposit thick layers (>100 µm) over large areas. CEA-LITEN has developed an innovative approach for depositing inorganic perovskites using close-space sublimation (CSS), which meets these criteria. Very recently, it has been shown that it is possible to deposit FAPbBr3 using this method, marking a world first.
However, the growth mechanisms of FAPbBr3 and hybrid perovskites via CSS are largely misunderstood, and the possibilities offered by this deposition method are yet to be fully explored. Furthermore, these results are also extremely promising for PV applications, as similar growth is expected by substituting Br to form FAPbI3.
This thesis aims to (i) determine and optimize the growth conditions via CSS for FAPbBr3 layers, (ii) understand the growth mechanisms of FAPbBr3 through advanced characterizations (in-situ and ex-situ), and (iii) optimize devices for X-ray detection. The extension of this work to FAPbI3 for PV applications is also anticipated. The novelty of this approach and the potential to address multiple applications offer prospects for publications and patents.
Development of durable and flexible KNN piezoelectric materials: toward an alternative to lead-based ceramics and fluorinated polymers
The project aims to develop lead-free and PFAS-free (perfluoroalkyl and polyfluoroalkyl substances) piezoelectric thin films based on potassium sodium niobate (KNN) that are compatible with flexible substrates, in direct response to the growing regulatory and environmental constraints affecting conventional piezoelectric materials. PZT ceramics (lead titanate-zirconate) and PVDF polymers (polyvinylidene fluoride), which currently dominate the market, have significant limitations related to lead toxicity and the environmental persistence of PFAS, respectively. In this context, identifying sustainable and integrable alternative materials is a strategic priority for the CEA, particularly for flexible electronics applied to medical, embedded, and sustainable devices.
KNNs are among the most promising alternatives due to their high piezoelectric properties and high Curie temperature. However, their integration in the form of thin films remains severely limited by crystallization temperatures exceeding 600 °C, which are incompatible with polymer substrates. The project’s objective is to overcome this barrier by developing an innovative sol-gel combustion deposition process, enabling localized or global crystallization at low temperatures (<350 °C), compatible with flexible substrates. Beyond the KNN system, this approach could constitute
Modeling the CSS growth of CsPbBr3
Lead-halide perovskites, particularly CsPbBr3, are emerging as promising materials for X-ray detection in medical applications. This technology requires their deposition in thick layers (>100 µm), and close-space sublimation (CSS), initially developed by CEA-Liten, has shown highly encouraging results. However, this process remains poorly understood at the microscopic scale, and the relationship between microstructure and performance remains a major scientific and industrial challenge.
This thesis, in partnership with the SIMAP laboratory, aims to develop a comprehensive thermodynamic model of the CSS process. The candidate will (i) experimentally generate the essential thermodynamic data for modeling, (ii) simulate growth mechanisms, and (iii) validate them experimentally using dedicated instrumented growth furnaces and advanced characterization techniques. Machine learning tools will be implemented to establish predictive correlations between deposition parameters and layer properties.
The results will enable optimization of CsPbBr3 growth for more sensitive and stable X-ray detectors, with a strong impact on medical imaging. This work will also provide opportunities for high-impact publications and patents in a highly competitive field.
Enhancing Faradaic Efficiency in Protonic Ceramic Electrolysis Cells (PCCELs) through Electrolyte and Electrode–Electrolyte Interface Engineering
Proton conducting ceramic electrolysis cells (PCCELs), an advanced variant of solid oxide electrolysis cells (SOECs), enable the direct production of hydrogen through steam electrolysis using proton-conducting electrolytes. Unlike conventional SOECs, which rely on oxygen ion (O²?) conductors, PCCELs operate at lower temperatures (~400–600?°C vs. 750–850?°C for SOECs) due to their higher proton conductivity. This lower operating temperature helps reduce material degradation and overall system costs. While SOEC technology has reached industrial maturity, with large-scale deployment projects underway, the development of PCCELs remains limited by several scientific challenges. These include the difficulty of densifying electrolytes (such as BaCeO3–BaZrO3) without barium volatilization during high-temperature sintering; the proton transport limitations posed by grain boundaries; and the poor control of electrode–electrolyte interfaces. This thesis aims to improve the faradaic efficiency of PCCELs by optimizing the microstructure of the electrolyte and engineering high-quality interfaces through targeted surface treatments. The methodology includes cell fabrication, interface engineering, and electrochemical evaluation. The ultimate goal is to establish robust and scalable processing protocols that enable PCCELs to achieve faradaic efficiencies above 95%, compatible with industrial-scale deployment.
Potential synergy between NH3 and NaBH4 for improved H2 density and enhanced safety
The thesis focuses on the study of the hybrid ammonia–sodium borohydride system (NH3–NaBH4) as an innovative chemical energy carrier. The objective is to investigate the combination of ammonia (NH3), recognised for its high hydrogen density and mature industrial infrastructure, with sodium borohydride (NaBH4), a high-capacity chemical hydrogen storage material, in order to overcome certain limitations associated with each vector when considered separately.
The proposed work specifically addresses the safer storage and transport of ammonia through its coupling with sodium borohydride, enabling a reduction in vapour pressure (compared to 8.88 bar at 21 °C for liquid ammonia) and less restrictive operating conditions. In parallel, the thesis aims to improve the stability (relative to the H2O–NaBH4 system) and operability of sodium borohydride which, when combined with ammonia molecules (acting as inert species), forms stable liquid or viscous phases that are potentially pumpable, thereby facilitating integration into energy-related processes.
The fundamental goal of the thesis is to understand the physicochemical mechanisms governing this hybrid system, particularly the role of dihydrogen interactions between the N–H bonds of ammonia and the B–H bonds of borohydride, and their influence on stability, reactivity, transport properties, and hydrogen release pathways (thermal and/or hydrolytic).
Beyond its storage function, the thesis also explores the potential of the NH3–NaBH4 system as a novel hybrid material with high gravimetric and volumetric hydrogen capacity, while considering realistic operational constraints relevant to energy applications in a dual-use context. At this stage, exhaustive optimisation is not the primary objective.
High-throughput screening of catalysts for the direct conversion of CO2 into synthetic fuels
This doctoral project aims to develop an innovative high-throughput screening approach for catalysts for the direct conversion of CO2 into synthetic fuels, known as CO2-FTS. This approach will combine a catalyst screening platform with in situ/operando characterization techniques and artificial intelligence methods to accelerate the discovery and optimization of high-performance catalysts. It aims to identify doped FeOx-type catalysts for the CO2-FTS reaction (>50% conversion, high selectivity towards C8-C16). Several high-throughput screening campaigns will allow for iterative optimization of compositions and reactive conditions. A numerical model of the parametric landscape will then be developed. This model will subsequently be coupled with multi-scale modeling from the active site to the reactor level. The developed catalysts will contribute to the energy transition by enabling a circular carbon economy.