Mickael Dollé

Impedance study of the Li○/electrolyte interface upon cycling

Abstract The Li/electrolyte interface of Li/LiMn2O4 plastic batteries was characterized during galvanostatic cycling by means of impedance spectroscopy. The impedance diagrams acquired during the charge and discharge of the battery were modeled and interpreted, in order to determine the lithium plating/stripping processes on the Li°-electrode. By means of known Li°/electrolyte interface models, a mechanism was then proposed by considering the passivation film and charge transfer effects. These results were also confirmed by three-electrode measurements.

Li-Driven Copper Extrusion/Re-injection in Various Cu-based Oxides and Sulfides

The present paper is in part a continuation of our recent work dealing with the fully reversible Li-driven Cu extrusion/injection of Cu in Cu2.33V4O11. The peculiar electrochemical property of such a compound was mainly ascribed to both structural considerations (presence of anchoring oxygen, giving flexibility to the [V4O11] layers) and electronic considerations, such as the existence of a delicate balance between the two Cu+/Cu2+ and V4+/V5+ redox centers. To support such suggestions, numerous compounds were revisited for their electrochemical–structural interplay. Network dimensionality, lattice flexibility, and cationic mobility parameters were addressed by exploring in depth the richness of the Cu–V–O system, while the importance of the donor/acceptor energy levels was checked via the choice of compounds having the right energy match between the two redox centers. As an extensive trial-and-error approach was not realistic, we relied on simple considerations based on the ionization energy of the various d-metals to narrow down metal pairs having redox levels occurring within the same range of energies. Bearing this in mind, it was logical to consider compounds still containing Cu ions but with Nb instead of V or compounds having V and Ag instead of Cu. Regardless of our effort, it turned out that the number of potential candidates worth considering for practical applications is still very limited, in spite of the elegance of this new Li reactivity mechanism.

Electrical properties of ferroelectric BiMnO3–PbTiO3 under tailored synthesis and ceramic processing

Conductivity is a main issue in research on multiferroic perovskite oxides, which makes the characterization of their ferroelectric properties difficult, and for several compounds even to unambiguously state their ferroelectric nature. In this report, we use ferroelectric BiMnO3–PbTiO3 as a model system to study the relationships among synthesis, processing, and conductivity in ABO3 perovskite oxides with magnetically active cations in the B-site. Three single phase, dense ceramic materials processed by conventional sintering, hot pressing, or spark plasma sintering (SPS) of powders synthesized by either wet chemistry or mechanochemical activation were studied. Impedance spectroscopy analysis was carried out to obtain grain and grain boundary conductivities for the three materials, along with activation energies. Mechanosynthesis is shown not to modify the mechanism of bulk or boundary conductivity, but only the carrier concentration, while SPS processing results in a low temperature, additional conduction mechanism.

Strain analysis by inversion of coherent Bragg X-ray diffraction intensity: the illumination problem

Bragg coherent X-ray diffraction imaging is demonstrated with a micro-focused illumination. The 2D projected density of the 3D nano-crystal is successfully retrieved from the inversion of its diffraction intensity pattern. The analysis of the phase field at the sample position, which holds in principle the strain information, emphasizes the high sensitivity of the technique with regard to the wavefront structure. The ptychography approach is a proposed solution to discriminate the wavefront function from the sample electron density distribution. It is based on a redundancy of the collected information obtained by measuring a series of diffraction patterns for different but overlapping beam positions onto the sample. Applicability to the Bragg geometry still needs to be demonstrated.

Influence of Microstructural Parameters on the Sintering of Transition Metal Carbides

In the frame of the development of new nuclear reactors (Gen-IV project), materials able to withstand very high temperatures are required. Among the components of the cores, the transition metal carbides could be favourably considered as fission products barriers or inert matrix for the fuel. They are highly refractory, have good neutron properties and fission products retention. Unfortunately, first they are brittle and second the elaboration process of bulk materials requires drastical conditions (temperature, pressure). We have then undertaken the comparison of different materials to investigate the potentialities of nano-sized microstructures for the improvement of the mechanical properties and to determine the impact of different elaboration routes to obtain high density articles. The elaboration process of the nano-sized powders is presented elsewhere [M. Dollé et al., this meeting]. Here, we compare different sintering processes (uniaxial hot-pressing, spark plasma sintering) and we present a new process able to produce high density zirconium carbide articles with soft conditions. We show that the sintering of co-ground zirconium and graphite powders lead to high density, homogeneous, low grain-size materials at temperatures as low as 1500°C. At the contrary, the nano-powders appear to be more difficult to densify that classical micro-sized powders.

Nano-Sized Zirconium Carbides: Synthesis, Characterisation and Irradiation

The projects of a new generation of nuclear plants with improved yield and drastical reduction of waste production make necessary the development of materials able to withstand high temperature (1000-1200°C) in normal conditions. New materials such as the refractory transition metal carbides are then considered. These materials have a ceramic-like, brittle behaviour. Their mechanical properties might be improved by decreasing the particles size at a nanometer level. The behaviour under irradiation of such nano-sized materials have then to be compared with classical micro-sized ones. High density, nano-sized materials have been obtained by two different sintering techniques. In order to simulate neutron irradiation, the samples were irradiated with low energy heavy ions. Consequently, the damaged material has a low thickness (100-200 nm), requiring surface analysis methods. Here, the grazing incidence X-ray diffraction method is used. From a Rietveld analysis of the diffraction patterns, the micro-sized materials show a linear volume swelling in the range 20-40 dpa in the Zr sublattice. Nano- and micro-sized materials both show high internal distortions.