Pierre-Emmanuel Lippens

Interpretation of the 119Sn Mössbauer parameters

The variations of the 119Sn Mössbauer isomer shift δ are interpreted for tin compounds from a semi-empirical tight-binding calculation of the electronic density at the nucleus ρ(0). A molecular model is proposed in order to relate the variations of ρ(0) for the Sn(IV) chalcogenides to the changes in the Sn environment. The variations of the experimental values of the quadrupole splitting δ are linearly correlated to the values of the electric field gradients (EFG) calculated by the full-potential linearized-augmented-plane-wave (FP-LAPW) method. The value of the 119Sn nuclear quadrupole moment is found to be |Q| = 10.5 ± 0.2 fm2. Finally, the relation between the EFG and the Sn environment is discussed for SnO.

Sb LIII-edge XAS study of the ternary system Sb2S3As2S3Tl2S

Abstract The local environment of antimony atoms in glassy samples of the system Sb2S3As2S3Tl2S is studied by X-ray absorption spectroscopy at the Sb LIII-edge. The crystalline compound TlSb3S5, situated within the zone of glass formation of the Sb2S3As2S3Tl2S phase diagram, is used as reference compound in order to derive appropriate phase and amplitude functions for the extended X-ray absorption fine structure (EXAFS) study. The limits of EXAFS in studying the local order around antimony in compounds with complex structure are discussed. The possibilities of a combined application of EXAFS, X-ray absorption near edge structure and 121Sb Mossbauer spectroscopy to the study of these compounds are shown. The results are discussed in terms of a model of random substitution of arsenic by antimony.

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.

A structural study of glasses in the As2S3Sb2S3Tl2S system

Abstract The local structure around As for glasses in the system As 2 S 3 Sb 2 S 3 Tl 2 S has been studied by measuring the extended X-ray absorption fine structure (EXAFS) at the As K edge and by differential scanning calorimetry. The variation of the EXAFS parameters and of the glass transition temperature as a function of the Sb 2 S 3 concentration has been analyzed for three systems containing 0, 20 and 40 mol% Tl 2 S. For all the glasses, As is found to be surrounded by 3 ± 0.2 sulfur atoms. The main trends in the variation of the average AsS interatomic distance and the Debye-Waller factor are explained in terms of a simple structural model involving AsS 3 and SbS 3 pyramidal units. The pyramids are linked by the S atoms (bridging sulfur atoms) or are not linked (non-bridging sulfur atoms) depending on the Tl 2 S content. The effect of the addition of Tl 2 S has been confirmed by a study of glasses in the As 2 S 3 Tl 2 S system.

Calculation of 121Sb and 125Te Mössbauer Spectra

We propose an alternative approach for the analysis of the Mössbauer spectra of complex crystalline materials when the determination of the Mössbauer parameters from the only experimental data fails. This approach is based on first principle calculations of the electron density and electric field gradients at the nucleus based on the linearized augmented plane wave method. Results are given for tellurium and antimony compounds.

Sulfur K-edge XAS study of As2S3Sb2S3Tl2S glasses

Abstract The local environment of sulfur in amorphous As2S3Sb2S3Tl2S was studied by XAS at the sulfur K-edge. Variations in shape and position of the white line are attributed to changes in the nature of the chemical bond, the metalsulfur bond lengths, and the homogeneity of the metalsulfur bond length distribution. The variations of the white line parameters, position and line width, with sample composition reveal the different influences of the glass-forming arsenic sulfide and antimony sulfide and the glass modifying thallium sulfide.

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.

First Principles Calculations of Mossbauer Spectra of Intermetallic Anodes for Lithium-Ion Batteries

Changes in 119Sn and 121Sb Mossbauer spectra due to lithium insertion in tin and antimony based anode materials for lithium-ion batteries are analysed. Due to the complexity of the spectra linear augmented plane wave calculations of the electronic density were used to evaluate the electron density and the electric field gradients at the nucleus. The 119Sn Mossbauer spectrum of SnO + 3.5 Li was evaluated from the theoretical spectra of the Li—Sn alloys. The observed good agreement between experimental and ab initio spectra is consistent with the reversible lithium insertion mechanism based on the formation of Li—Sn alloys. The analysis of the 121 Sb Mossbauer spectra for Li insertion into CoSb3 is somewhat more complex but calculations of the Mossbauer parameters clearly indicate the existence of Li3Sb at the end of the first discharge.

Phase separation and amorphisation in lithium inserted Cu–In–Sn sulfospinels: experimental and theoretical approach

Abstract 119 Sn Mossbauer spectroscopy, X-ray diffraction (XRD) and electrochemical experiments were carried out to characterise the reaction mechanism of lithium with spinel phases Cu x In y Sn z S 4 . The electrochemical investigations have shown interesting reversible capacities for these materials, and their possible use as anode materials in lithium-ion cells. This analysis reveals a multi-phase mechanism linked to the reduction of the cations involving a spinel to rocksalt transformation followed by a structural breakdown. Density functional calculations by the linearised augmented plane wave (LAPW) method give a good interpretation of experimental results for crystalline phases.