People involved in the research topic :
Guy OUVRARD (Pr), Philippe MOREAU (MC), Florent BOUCHER (CR)

• Collaborations
• Publications

Figure 1

Figure 2

Figure 1 and 2 : in order to identify a poorly crystallised C3N4 lamellar compound, it was necessary to first perfectly simulate EELS spectra at the C and N K-edges. We first focussed on model compound (i.e. graphite and h-BN) and proposed a partition of the EELS spectra between a low energy part and a higher one. The simulation are then very close to the experimental spectra using a strong core hole at low energy and no core-hole at high energy. The results obtained for the C K-dege in graphite and B K-edge in h-BN are shown in Fig 6a and 6b respectively. (Collaboration G. Goglio). To read more.

Figure 3- EELS spectra depend strongly on the experimental setup (angles, beam energy... ). We studied precisely these parameters and their influence on Low Energy-Loss Spectra of BN nanofibers (To read more). Using this experience, we could identify with confidence a rutile phase characteristic peak in Low Energy-Loss Spectra of rutile TiO₂ and other rutile dioxides (MO₂ ; M= V, Mn..). In this figure, experimental and theoretical spectra are compared. The characteristic peak is the one at 14 eV. The interband transition responsible for this peak was precisely identified. (To read more) (DEA of M. Launay)

Figure 4

Figure 4 : In order to get a better understanding of the electrochemichal process at work in lithium ion batteries, we performed EELS experiments at the lithium K edge on an anode material: LixTiP4. We also carried out first principle calculations (WIEN2k) on hypothetical structures for a Li₂TiP₄ composition. We simulated different site occupations: namely 2 lithium atoms in tetrahedral sites, or two in octahedral sites, or one each possible site symmetry. We compare in Figure 9, the resulting simulations with the experimental results and show that for low lithium compositions the lithium atoms are intercalated in tetrahedral sites. Other experiments also give information on the biphasic process occuring during the cycling of the battery. From Vincent Mauchamp PhD thesis.

To read more.

Vincent Mauchamp PhD thesis is available here (14Mo pdf file, only in french, sorry).

Figure 5: imaginary part of the dielectric function compared to the loss function, Im(-1/epsilon), for Li and LiMn₂O₄. These calculations demonstrate the influence of polarization effects when a transition metal edge is situated in the vicinity of the lithium K edge. In fact, the real part of the dielectric function should also be taken into account, and not only the imaginary part of the dielectric function. From Vincent Mauchamp PhD thesis. To read more .

Figure 5