Laurent Aldon

Lithium insertion mechanism in Sb-based electrode materials from 121Sb Mössbauer spectrometry

Abstract Lithium insertion mechanism in some antimony-based compounds: SnSb, CoSb3, CrSb2, TiSb2 has been studied by means of 121 Sb Mossbauer spectrometry which gives valuable information about the local electronic structure of the probed element (Sb). The structural and electronic modifications induced by insertion of lithium have been characterized. For these Sb-based materials the lithium insertion mechanisms involve Li3Sb formation and composite multi-phase separations with one component displaced from the pristine compound.

Structural and electronic modifications induced by lithium insertion in Sn-based oxide glasses

Abstract The irreversible mechanisms of lithium insertion in amorphous tin composite oxides SnB 0.6 P 0.4 O 2.9 have been studied by X-ray diffraction (XRD) and 119 Sn Mossbauer spectroscopy. The determination of the Lamb–Mossbauer factor has allowed us to evaluate the relative numbers of different tin atoms (Sn II , Sn 0 ). We show that insertion of lithium reduces the Sn II into Sn 0 atoms, which form nanoparticles of active species. The lithium ions act as glass modifiers, breaking the bonds within MOM′ (M, M′=B, P, Sn) bridges and forming non-bridging MO δ − bonds.

In situ 119Sn Mössbauer spectroscopy study of Sn-based electrode materials

Sn-based composite materials were synthetized by a conventional melt-quenching method, and studied by X-ray diffraction, electrochemistry and in situ119Sn Mösssbauer spectroscopy. Tin was dispersed ex situ into a matrix formed from B2O3:P2O5. XRD and 119Sn Mössbauer spectroscopy show the formation of an interface between the active species (Sn0) and the matrix. This amorphous interface acts as a “buffer-zone” which compensates volume changes during the tin–lithium alloy formation and avoids aggregation of tin particles.

Crystal structure of the non-stoichiometric argyrodite compound Ag7-xGeSe5I1-x (x = 0.31). A highly disordered silver superionic conducting material

Abstract Single crystals of the Ag6.69GeSe5I0.69 phase have been obtained by iodine transport of the iodine-partially substituted stoichiometric argyrodite compound Ag7GeSe5I. This phase crystallizes in the cubic space group F 4 3m (argyrodite γ-phase, a=10.921(2) A at −100°C, a=10.972(3) A at 25°C, Z=4). It is highly disordered both at anion and cation sites. Crystal structure refinements were completed by an anharmonic Gram–Charlier development of the atomic displacement factors of iodine and silver atoms. The structure of Ag6.69GeSe5I0.69 was determined at −100°C and +25°C and was refined to R(F) values of 5.80 and 6.51%, respectively. Both iodine and selenium (Se1) anions have been found disordered and iodine is slightly defective on its crystallographic site. This is correlated to the disorder observed for the two Ag1 and Ag2 cations that provides this material with superionic conducting properties. Analysis of the joint probability density function allowed the visualization of the Ag+ diffusion paths within the anionic framework.

In situ 119Sn Mössbauer spectroscopy used to study lithium insertion in c-Mg2Sn

The electrochemical reactions of Li with c-Mg2Sn have been investigated by in situ Mössbauer spectroscopy of 119Sn and X-ray diffraction. The lithiation transforms initially c-Mg2Sn part into LixMg2Sn alloy (x < 0.5). On further lithiation Mg is extruded from the structure with formation of Li2MgSn ternary alloy. In situ Mössbauer spectroscopy provides valuable information on local environment of tin and swelling behavior and cracking of the particles during discharge and charge processes.

Local electronic structure of Tl–Sn–Te compounds

Abstract We show that the combined application of Mossbauer spectroscopy and X-ray photoelectron spectroscopy (XPS) provides a consistent picture of the local electronic structure in Tl 5 Te 3 , TlTe, Tl 2 Te 3 , Tl 4 SnTe 3 and Tl 2 SnTe 5 . The results are discussed from a tight-binding calculation of the electronic populations. We show that values of the Tl 4f 7/2 core-level binding energy do not vary noticeably for the different compounds in agreement with the close values of the calculated Tl average charges. The results obtained by both the XPS and 125 Te Mossbauer spectroscopy are consistent with the existence of two types of Te atoms with very different atomic charges due to the differences in the number of Te 5p electrons. The variations of the Te charge are explained from changes in the nature of the Te nearest neighbors: Tl, Sn and Te as a function of the stoichiometry. Finally, we show that values of the 119 Sn Mossbauer isomer shift and the Sn 4d 5/2 core-level binding energy both increase from Tl 2 SnTe 5 to Tl 4 SnTe 3 in agreement with the increase of the calculated number of Sn 5s electrons and the decrease of the calculated number of Sn 5p electrons, respectively. These changes are related to the differences between the Sn local environments of the two ternary compounds.

Electronic structure of Ge–As–Te glasses

Abstract The electronic structure of Ge 0.2 Te 0.8 and Ge 0.1 As x Te 0.9− x glasses with x =0.2, 0.46 and 0.54 has been experimentally determined by X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The values of the Ge 3p 3/2 , As 3p 3/2 and Te 3d 5/2 core level binding energy do not vary significantly within this series of glasses in agreement with the covalent character of the bonds. The atomic contributions to the main observed peaks in the XPS valence bands and XAS spectra are obtained from a molecular calculation. This approach is first used for crystalline As 2 Te 3 and compared to a periodic tight-binding calculation in order to check its accuracy for the analysis of the experimental data in terms of local environments. The electronic structure of Ge 0.2 Te 0.8 is consistent with the existence of GeTe 4 units connected by Te–Te bonds but does not rule out the presence of Ge–Ge bonds. The XPS valence bands of the ternary glasses are formed by two broad bands which are due to the s- and p-type valence electrons of the different atoms, respectively. Increase of the As content mainly changes the p-type peak and the main XAS peaks at the As K and Ge K edges. These changes are due to the decrease in the number of As–Te bonds and the increase in the number of As–As bonds.

Characterization of Li insertion mechanisms in negative electrode materials for Li-ion batteries by Mössbauer spectroscopy and first-principles calculations

The Mossbauer spectroscopy is an efficient experimental tool to study lithium insertion mechanisms in negative electrodes of Li-ion batteries at the atomic scale. However, a quantitative interpretation of the experimental data is often difficult due to the complexity of the spectra and we propose to use first-principle calculations of the hyperfine parameters. Three different types of negative electrode materials are considered. First, the experimental 119 Sn Mossbauer spectrum obtained for the insertion of 3.5 Li into SnO is compared to the theoretical spectrum, which clearly establishes the existence of Li-Sn stable phases. Then, the analysis of the 121 Sb Mossbauer spectra for metal antimonides at the end of the first discharge shows different behaviours depending on the lithium rate. Finally, tin and iron doped titanates are considered to study changes in Ti local environments during lithium insertion.

Mössbauer Spectrometry as a Powerful Tool to Study Lithium Reactivity Mechanisms for Battery Electrode Materials

The use of 57Fe as a local Mossbauer probe is of high interest for studying mechanisms induced by lithium insertion. In this way the substitutions Ti/Fe and Li/Fe have been carried out for Li4Ti5O12 to obtain Fe substituted spinel and Li2Ti3O7 ramsdellite. In the case of Li4Ti5O12 iron ions are reduced (FeIII → FeII), then migrate from tetrahedral to octahedral sites allowing us to establish the spinel ↔ rocksalt phase transition. Such phase transition definitively explains the well-defined plateau observed in the electrochemical potential curves. In the case of Li2Ti3O7 ramsdellite, all the iron ions are located on octahedral sites and the quadrupole splittings are related to the number of lithium in the neighbourhood of probed atoms.

Ionic and electronic transport in In2S3 studied via perturbed angular correlation spectroscopy

We report on Perturbed Angular Correlation measurements in polycrystalline In2S3 samples in the temperature range from 8 K to 1000 K where two different crystallographic phases β and α occur. As probes, implanted 111In nuclei have been used. The three observed EFGs are attributed to probes residing substitutionally in the different sulfur-octahedra and -tetrahedra of β-In2S3. A strong damping between 150 K and 300 K has been attributed to EFG fluctuations following the 111In(EC)111Cd decay. The α-phase (above 680 K) is characterized by a different dynamical damping of the perturbation functions, caused by mobile In atoms. Therefore, the semiconductor In2S3 shows, in two different temperature ranges, dynamical PAC-spectra which correspond to different types of mobile charge carriers. Since 111In is a self atom in In2S3, this compound is an ideal substance to study the charge transport phenomena by the PAC technique.