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International audience; The performances of Li-ion batteries depend on many factors amongst which the important ones are the electrode materials and their structural and electronic evolution upon cycling. For a better understanding of lithium reactivity mechanism of many materials the combination of X-Ray Powder Diffraction (XRPD) and Transmission Mössbauer Spectroscopy (TMS) providing both structural and electronic information during the electrochemical cycling has been carried out. Thanks to the design of a specific electrochemical cell, derived from a conventional Swagelock cell, such measurements have been realised in operando mode. Two examples illustrate the greatness of combining XRPD and TMS for the study of LiFe0.75Mn0.25PO4 as positive electrode and TiSnSb as negative electrode. Different kinds of insertion or conversion reactions have been identified leading to a better optimization and design of performing electrodes.

The electrochemical reaction mechanism of the Sn–(CaSiO 3 ) 0.4 composite electrode with Li was investigated by electrochemical tests and a variety of spectroscopic techniques. The electrochemical behavior of this material showed a highly reversible reaction with Li after the first discharge with a specific capacity of 530 mAh g −1 at C/10 rate. Some essential steps of the mechanism have been inferred from 119 Sn Mossbauer spectroscopy and the electrochemical potential curve. The composite material contains three tin based phases with different tin oxidation numbers: an amorphous Sn II phase which is reduced into Sn 0 as the first step of the discharge, CaSn IV SiO 5 and β-Sn which are progressively transformed into lithium–tin alloys during the discharge. A Mossbauer spectrum recorded at the end of the discharge reveals the formation of Li 7 Sn 2 . The de-alloying reaction of Li 7 Sn 2 leads to the formation of β-Sn at the end of the charge. X-ray absorption and 119 Sn Mossbauer spectroscopy revealed furthermore that the electrochemical reaction between Li and the Sn–(CaSiO 3 ) 0.4 composite is accompanied by an electron transfer between Li and Sn.

An original carbothermal synthesis of ramsdellites phases under specific atmosphere (Ar, Ar/H 2 , N 2 , N 2 /H 2 ) allowed creating in situ composites which showed good electrochemical properties as negative active materials of Li-ion batteries. The combination of chemical, XRD and electrochemical analyses enabled to identify the as-formed composite electrodes. It consists in ramsdellite/spinel for the synthesis under Ar/H 2 , TiO 2 ramsdellite/Li 2 TiO 3 for the synthesis under N 2 /H 2 , and Li 2± x Ti 3 O 7 /Li 2± x ′ Ti 3 O 7 for the samples prepared under both N 2 and Ar. Carbon is partially inserted inside channels of titanate structure for the sample obtained under Ar/H 2 . For the first time, one of these composites allowed reaching a specific capacity close to the theoretical value of 198 mAh g −1 .

Ni 3 Sn 4 and CoSn 2 which are two Sn-based intermetallic compounds with different crystal structures have been tested as future negative electrodes for lithium-ion batteries. Various two-step reactions occur during the first discharge of these two electrodes. The first discharge shows good specific capacities: 515 mAh g −1 for the Ni 3 Sn 4 electrode and 606 mAh g −1 for the CoSn 2 electrode. These reactions lead to the formation of Li 7 Sn 2 , a Li-rich Li x Sn alloy characterized by 119 Sn Mossbauer spectroscopy.

The reaction mechanisms between Sn-(n-C4H9)4 and several specific types of surface sites on alumina are studied. A surface treatment is described allowing the complete elimination of reactive surface sites and avoiding the anchoring of Sn-(n-C4H9)4 on the support. This surface deactivation is applied to the preparation of bimetallic PtSn/Al2O3 catalysts by controlled selective decomposition of Sn-(n-C4H9)4 on the reduced metallic particles of a Pt/Al2O3 catalyst. The resulting bimetallic particles are analysed by 119Sn Mossbauer spectroscopy at different stages of the preparation procedure. The tin anchoring sites on the platinum particles are identified on the basis of their specific Mossbauer hyperfine parameters. Tin atoms in contact with the support or with platinum are distinguished from those enclosed in bulk-SnO2-like agglomerates. A structural model is proposed describing at an atomic scale the morphology of the bimetallic particles and their evolution under various heat treatments. The results are compared with those of a catalyst prepared by conventional impregnation methods on a not specifically pretreated support.

Several Li–Sn crystalline phases, i.e. Li 2 Sn 5 , LiSn, Li 7 Sn 3 , Li 5 Sn 2 , Li 13 Sn 5 , Li 7 Sn 2 and Li 22 Sn 5 were prepared by ball-milling and characterized by X-ray powder diffraction and 119 Sn Mossbauer spectroscopy. The analysis of the Mossbauer hyperfine parameters, i.e. isomer shift ( δ ) and quadrupole splitting ( Δ ), made it possible to define two types of Li–Sn compounds: the Sn-richest compounds (Li 2 Sn 5 , LiSn) and the Li-richest compounds (Li 7 Sn 3 , Li 5 Sn 2 , Li 13 Sn 5 , Li 7 Sn 2 , Li 22 Sn 5 ). The isomer shift values ranged from 2.56 to 2.38 mm s −1 for Li 2 Sn 5 , LiSn and from 2.07 to 1.83 mm s −1 for Li 7 Sn 3 , Li 5 Sn 2 , Li 13 Sn 5 , Li 7 Sn 2 and Li 22 Sn 5 , respectively. A Δ − δ correlation diagram is introduced in order to identify the different phases observed during the electrochemical process of new Sn-based materials. This approach is illustrated by the identification of the phases obtained at the end of the first discharge of η -Cu 6 Sn 5 and SnB 0.6 P 0.4 O 2.9 .

Electrochemistry requires a stable structure to avoid capacity loss. Substitution of structural Ti and Li by 3d transition elements in the Li2Ti3O7 ramsdellite structure has been considered in order to improve the accessibility of the vacancies. In the case of a one element substitution, Ti/Fe, the reduction FeIII to FeII gives rise to an irreversible part in the electrochemical curves. For the substitution of Ti/Li by two transition elements, Fe and Ni, only a partial FeIII/FeII reduction occurs, resulting in a smaller irreversible plateau and improved cyclability. This reduction has also been evidenced by 57Fe Mossbauer spectroscopy in which 57Fe is used as a local probe giving valuable information about its local environment, thus allowing deeper insight into the lithium insertion mechanism.

For the search of new negative electrodes of Li-ion batteries, a low-temperature method has been developed for the preparation of nanoscale antimony particles which uses an alkoxide-activated sodium hydride as reducing agent of antimony pentachloride. X-ray diffraction and TEM studies confirm the obtaining of amorphous Sb nanoparticles dispersed in an organic matrix. 121Sb Mossbauer spectroscopy gives evidence for the occurrence of interactions between antimony and the matrix. These interactions are modified by the washing treatments.

119Sn Mossbauer spectroscopy at 77 K was used to observe surface tin atoms on PtSnx/SiO2 catalysts. Two families of PtSnx/SiO2 catalysts with fully reduced Pt(0) and Sn(0) atoms were prepared following the Surface Organo-metallic Chemistry on Metal strategy. These two families of catalysts exhibit about the same Sn/Pt composition, but very different metallic particle diameters, each with narrow particle size distribution, so that, the ratio between surface tin atoms and “bulk” tin atoms was significantly different for the two families. In addition to the well known “Pt-Sn” bulk alloy with small quadripole splitting, a new Pt-Sn species with large quadripole splitting and isomer shift in the range of Sn(0) was observed. The relative proportion of this species with respect to “Pt-Sn” bulk alloy is greater for small particles than for the larger ones, which suggests that this species is a surface tin atom present in a “Pt-Sn” alloy.

A high-voltage (5 V) LiCo 0.8 Fe 0.2 MnO 4 electrode with spinel-type structure has been prepared. 57 Fe Mossbauer spectra reveal high-spin Fe 3+ ions in octahedral coordination in the pristine sample, which are oxidized to tetravalent iron ions. Surface treatments with zinc and magnesium have been applied. Zinc and magnesium were homogenously distributed, according to EPMA and mapping analysis, while the spinel structure is maintained. The magnesium and the zinc treatments drive to better electrochemical performance and capacity retention.

Surface organometallic chemistry has been used to deposit tin atoms on an alumina-supported cobalt–molybdenum sulfide. The EXAFS spectra at the Mo and Co K-edges were not changed significantly by tin doping, which means that the initial morphology of sulfide phases was preserved during the synthesis. 119 Sn Mossbauer spectroscopy indicated that the main neighbors of the deposited tin atoms were sulfur and oxygen atoms with no significant formation of metallic tin particles. Tin seems thus to have been deposited either on the sulfide slabs through sulfur bridges or on the support via oxygen bonding. According to the infrared spectroscopy, tin doping led to the blocking of different surface sites with slight electronic structure modification. Those surface sites are sulfur vacancies on sulfide slabs, Al3+ or hydroxyl groups on the support, or “interfacial” sites: support hydroxyl groups H-bonded with sulfide phases. The impact of tin doping on the activity and selectivity of the sulfide phases was studied by catalytic tests carried out using a synthetic FCC gasoline feed. Three main reactions were found to be involved: hydrodesulfurization of sulfur-containing molecules, double-bond isomerization and hydrogenation of olefins. Olefin hydrogenation was preceded by double-bond isomerization reaction, which gave quickly thermodynamically equilibrated composition. No clear correlation could be made between tin doping and isomerization performance and catalyst support was proposed as the main actor for this reaction. Small amounts of tin had little effect on the hydrogenation activity, but higher loadings resulted in an important decrease in activity. Contrary to the case of olefin hydrogenation, thiophene hydrodesulfurization activity decreased drastically at a low tin loading, and continued to decrease but more slightly at higher loadings. By comparison of the activity variations and the characterization results, the sulfur vacancies were found to play a major role in the hydrodesulfurization process. Interfacial sites were assumed to be involved in one of the key steps in the olefin hydrogenation pathway.

Lithium reaction mechanism in amorphous tin composite oxide SnB0.6P0.4O2.9 is characterized by X-ray diffraction, 119Sn Mossbauer spectroscopy and X-ray absorption fine structure. The analysis of the experimental data concerning SnB0.6P0.4O2.9 shows that SnII is highly ionic and is surrounded by three oxygen atoms. The detailed analysis of lithium insertion mechanism shows a complex reduction mechanism in two steps. During the first one the main reaction corresponds to a partial SnII reduction, involving a mixed valence system. It is accompanied by modifications of tin environments, while lithium acts as a network modifier inducing the formation of nonbridging oxygen atoms. The second step corresponds to LiSn alloying process, with the formation of LiSn bonds. It is worth noting the persistence of SnO interactions in this second step. The reversible part of the mechanism can be explained from the formation of small particles of lithium–tin alloys in strong interaction with the oxygen atoms in the glass matrix, while the vitreous support presents an interesting dispersal effect.

Colloidal oxide synthesis is a new technique for the preparation of bimetallic supported particles which provides the opportunity to control particle size distribution and interaction between both metals. It consists in synthesizing in aqueous medium a sol of colloidal oxide Pd–Sn nanoparticles which is further deposited onto a porous support. In this work, this method has been applied to the preparation of Pd–Sn/Al2O3 dedicated to the selective hydrogenation of unsaturated hydrocarbons. Two synthesis routes, surface precipitation and surface adsorption, are described to demonstrate the potential of colloidal oxide chemistry to generate a bimetallic interaction in aqueous solution which is strengthened during the reduction step after deposition onto alumina. 119Sn Mossbauer spectroscopy (119Sn MS) and transmission electron microscopy (TEM) were used to characterize the sols and the supported catalysts. This allowed us to determine the key parameters of colloidal oxide synthesis as far as formation of bimetallic PdxSny phases is concerned.

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.

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.

The spinel Li4Ti5O12, a stable phase of the Li2O–TiO2 system, allows to insert three Li atoms per formula unit at a potential of 1.5 V on the basis of a spinel ↔ NaCl phase transition. This mechanism leads to a reduction of three Ti(IV) atoms out of five, corresponding to a theoretical capacity of 175 mAh/g. The influence of structural defaults on the spinel → NaCl phase transition and its reversibility during charge/discharge cycles have been studied. Solid solutions formed from chemical insertion of lithium or substitutions Ti/V, Ti/Mn, Ti/Fe modify the cation distribution on the crystallographic sites (tetrahedral 8a, octahedral 16d, space group Fd3m) and influence the electrochemical performances. A structural analysis by X-ray and neutron diffraction, X-ray absorption, 57 Fe Mossbauer spectroscopy and first principle calculations have allowed to establish a relationship between the structure and the electrochemical properties.

The mixed transition-metal spinel oxide NiFe2O4 is used for the first time as active electrode materials vs. lithium metal in test cells. Reversible capacities close to 900 mAh/g are found. Due to the poorly crystalline nature of the products of electrochemical reaction, diffraction procedures give little information about the iron forms in the reaction products. The use of 57Fe Mössbauer spectroscopy allows to monitor the mechanism of the electrochemical reaction with lithium of the spinel. During the first discharge, the amorphization process is accompanied by metal reduction. The reversible redox reaction FeIII↔Fe0 accounts for the cycling capacity. However, magnetic ordering is lost during the first discharge and is not recovered in subsequent cycling or in the iron metal products. Keywords: Lithium batteries, Negative electrode, Mixed spinel oxides, Mössbauer spectroscopy, Iron oxide reduction

The modification of metal oxide surfaces by π-conjugated ferrocene units has been performed. A phosphonic acid functionality was used to covalently anchor the π-conjugated ferrocene moiety to SnO2 and TiO2 particles. The covalent attachment and the monolayer coverage at the surface of the particles were confirmed by solid-state MAS 31P NMR spectroscopy, microanalysis and electronic microscopy (EDX). The properties of the ferrocene-modified oxides were analysed by cyclic voltammetry, which confirmed the electroactivity of the material, and 57Fe Mossbauer spectrometry, which provided information about the oxidation state and environment of the iron atoms. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

The phosphate adsorption properties of three clay samples, with kaolinite as the dominant mineral, from different deposits in the Ivory Coast have been investigated. The clays contain varying amounts of crystalline Fe oxides and kaolinite with structural Fe. All measurements were made in dilute suspension under controlled conditions of temperature, pH, ionic strength and saturating cation. Data have been fitted to Langmuir adsorption isotherms. Both P adsorption and surface area measurements have been made on samples before and after chemical removal of Fe oxides. The samples have large P adsorption capacities, which are not entirely explained by their large specific surface areas. The presence of Fe oxides makes a strong contribution to the surface area and enhances the adsorption capacities. There is little evidence that structural Fe makes a strong contribution to the enhanced P adsorption capacity.

The solar thermochemical dissociation of H2O and CO2 for renewable fuel production from two-step SnO2/SnO cycle is considered. This cycle is based on the solar production of SnO phase in a first endothermic step that is subsequently used for splitting CO2 and H2O in a second exothermic step. The reactivity of tin-based species was studied in order to elucidate the phenomena occurring during its heating and subsequent reoxidation in a H2O or CO2 atmosphere to produce H2 or CO. Two main types of reactant were considered for comparing their reactivity: SnO nanopowder obtained via solar sublimation and condensation of commercial SnO powder, and Sn/SnO2 nanopowder obtained via disproportionation of nanosized SnO. The reaction rate was quantified via thermogravimetry analysis and the reaction products were characterized using Mossbauer spectrometry and X-ray diffraction. The SnO and Sn/SnO2 nanopowders are more reactive with H2O than with CO2 in the range 550–650 °C. SnO is also more reactive with oxidants than...

We studied the reduction mechanism of SnO in lithium cells by X-ray absorption near OK and SnL I edge spectroscopy, 119 Sn Mossbauer spectroscopy and X-ray diffraction. The reduction mechanism is complex, involving mixed valence intermediate compounds. In the interval 0≤Li/Sn≤2 the main reaction corresponds to a partial reduction of Sn II , which is partially reversible, regenerating the tin oxide during the charge. For Li/Sn greater than two, LiSn bonds are formed, but SnO interactions are still present. The charge within this interval also partially regenerates tin oxide, but the reversibility does not extend to Li/Sn lower than two. At low voltage and very large depth of discharge, the formation of LiSn alloys and Li 2 O clearly takes place, with negligible SnO interactions.

The metal−citrate method is applied to the preparation of microcrystalline tin dioxide and aluminum-doped materials. The effect of the precursor composition, referred to as the metal/citrate ratio, and the thermal treatment are discussed. The different compositions produce upon thermal decomposition rutile-type SnO2 solids. For Al-containing oxide materials, Al(III) ions occupy octahedral sites isomorphic to Sn(IV), as shown by 27Al MAS NMR signals at ≈0 ppm and 119Sn Mossbauer signals at 0 mm/s isomer shift and 0.53 mm/s quadrupole splitting, respectively. A large microstrain content is released by successive thermal treatments at 450 °C. Simultaneously, extended defects, which imply deviations from an MO2 stoichiometry, are found upon heating. These phenomena condition the ability of the oxide products to be used as the active anode material in lithium-ion batteries. The best electrochemical performance of lithium anode cells is achieved for 10% Al-containing ex biscitrate oxides in which ≈200 Ah/kg cap...

cited By 2; International audience; Electrochemical and chemical lithium insertion (via n-butyllithium) were carried out on a family of spinel phases of the Cu2S-In 2S3-SnS2 system. Electrochemical measurements have revealed great reversible capacities and the possible use of these materials as negative electrodes in lithium-ion batteries, ll9Sn Mössbauer spectroscopy, 7Li NMR and S K edge EXAFS spectroscopy were carried out to characterize the mechanisms of lithium insertion. This study has shown the formation of lithium-metal alloys finely dispersed in an amorphous lithium sulfide matrix at low potentials. A model is proposed to explain the great capacities observed in these materials.

A simple atomic model is described in which lithiation appears as a reversible pressure acting on confined atomic species which constitute the host material. It is demonstrated, by ab initio calculations of the properties of a confined atom as a function of the cavity radius, that the ionization of Sn occurs in the manner which has been observed, i.e., it passes directly from Sn IV to Sn II without the appearance of Sn III . This is shown not to be the case for a confined atom with no d shell present, and therefore we conclude that the observed property is of atomic origin and is directly related to the high compressibility of d orbitals. Extensions of our model are suggested to include relativistic effects, which would enable ab initio calculations of the Mossbauer signals to be attempted for the lithiated compounds. This would provide an independent test of our model.

The local environment of tin, titanium, iron, and sulfur in spinel compounds Cu2FeSn3S8 and Cu2FeTi3S8 was studied by X-ray absorption spectroscopy (XAS) at the titanium, iron, sulfur K edges, and the tin LI-edge. As detailed calculations of the electronic structure of these compounds are difficult to carry out due to the large number of atoms contained in the unit cell, the XAS spectra of the spinels are compared to those of relatively simple binary sulfides like SnS2, TiS2, and FeS. Indeed, the metal environments in these binary compounds are very similar to those in the spinels, and they can be considered good model compounds allowing the interpretation of electronic transitions observed in the spectra of quaternary phases. In the latter, the bottom of the conduction band is mainly formed by Sn 5s–S 3p, Sn 5p–S 3p antibonding states for the tin-based compounds and by Ti 3dt2g–S 3p, Ti 3deg–S 3p antibonding states for the titanium-based compounds. It it shown that the local environment of iron atoms remains unchanged when substituting tin with titanium atoms, according to a topotactic substitution.

The synthesis, structural determination, and electrochemical studies of Cu{sub 2}CoTi{sub x}Sn{sub 3 {minus}x}S{sub 8} solid solutions are reported. The evolution of the cubic spinel unit cell parameter with x shows two regions which are defined by the increasing covalency of the Ti-S bonds and the radii of the metal ions present in the solid. An increase in the isomer shift of the {sup 119}Sn Moessbauer spectra of these solids agrees with this interpretation. The solid solutions are used as active cathode materials in lithium cells. The discharge shows a complex reduction effect which is associated with the decrease in the oxidation state of Sn{sup 4+} and Ti{sup 4+} ions, accompanied by deep structural changes which end in the complete amorphization of the solid and the occurrence of tin in the metallic state. The extended discharge of the lithium cells leads to a good cycling behavior in galvanostatic experiments carried out in the 0--2.3 V interval, with capacities close to 400 mAh/g after 10 cycles.

The properties of suitable materials for electrodes of lithiumion rechargeable batteries are discussed. The key to understanding the insertion process is the localization of the ionic and electronic charge distribution in the lattice. A suitable sequence of spinel materials has been selected and investigated experimentally using a variety of techniques. The resulting observations are discussed in terms of an atomic model based on comparisons with known spectra and on ab initio Hartree–Fock calculations.

Cu{sub 2}MSn{sub 3}S{sub 8} (M = Fe, Co) spinel compounds have been studied as cathode materials in Li/LiPF{sub 6}(1M)-PC-EC/spinel sulfide cells. To understand the lithium insertion mechanism, both pristine compounds and chemically inserted products were characterized by X-ray Powder Diffraction (XPD), {sup 119}Sn Moessbauer Spectroscopy (MS), and X-ray Absorption Spectroscopy (XAS) at the sulfur K-edge. To accommodate the inserted lithium ions, two steps of reduction have been observed. First, for a low lithium content (up to 2 Li per formula), a copper reduction is occurring. Moreover, for the iron-based compound the copper atoms extraction is associated with a migration of iron atoms from the 16c octahedral sites toward the 8a tetrahedral sites. Second, for a high lithium content (above 2 Li per formula) a complex and simultaneous reduction of tin(IV) toward tin(II) and tin(0) has been clearly observed as well as a distortion of sulfur coordination polyhedra during the insertion process. From an electrochemical point of view, these spinels are rather interesting as model compounds regarding the lithium insertion study.

Tetragonal SnO compound was studied as the active electrode material in `Lithium-ion'-type cell. Structural and 119 Sn Mossbauer properties of SnO are presented. The results concerning X-ray powder diffraction (XRD) and 119 Sn Mossbauer spectroscopy of lithiated crystallised tin oxide SnO between 0 and 2 lithium inserted per formula were reported. During the lithium insertion a reduction of SnO in β-Sn and in an inter-metallic tin in strong interaction with the structural SnO (SnO→β-Sn and SnO→Sn(0)) is observed. When the cell is recharged, the mechanism is in part reversible with the reformation of the SnO but there is also the formation of Sn(IV) (Sn(0)→Sn(II)→Sn(IV)).

Cu 2 FeSn 3 S 8 and Cu 2 FeTi 3 S 8 spinel compounds have been used as electrode materials in lithium cell. The lithium insertion mechanism was studied by characterization of chemically lithiated (via n -butyllithium) samples using the X-ray powder diffraction and the 57 Fe Mossbauer spectroscopy. The intercalation process was correlated with the electrochemical behavior. Rietveld analysis of the tin based phase shows a weak extraction of copper between 0 and 2 lithium per formula. Along this extraction, a migration of iron cations from octahedral to tetrahedral sites was observed. Regarding titanium based thiospinel, the reduction of titanium occurs in two steps. Firstly titanium (IV) is reduced to Ti (III). Secondly, following the five already intercalated lithium, the Ti reduction process is occurring towards a lower oxidation state Ti(II).

A study by 119 Sn Mossbauer spectroscopy of lithiated tin β-Sn powder is presented for between 0 and 3.4 lithiums inserted per formula and for a thin foil of β-tin with between 0 and 2.8 lithiums inserted. This identifies the different Li–Sn alloys obtained electrochemically. We have identified two different sites. The first site corresponds to a tin with Sn–Sn bonds in a slightly distorted site. The second site is representative of Li–Sn bonds for tin in a more distorted site. In other respects, this study has allowed a better understanding of the complex tin reduction, which occurs during lithium insertion in tin oxide SnO.

The authors have studied the structural modifications that occur during electrochemical insertion of lithium into the spinel compound In{sub 16}Fe{sub 8}S{sub 32}. Studies by X-ray diffraction (Rietveld analysis) and Moessbauer spectroscopy of the lithiated products indicate that some cation migration takes place during the insertion process. The Moessbauer spectra show that no reduction of Fe{sup 2+} takes place during the insertion. The variation of the isomer shift indicates an increase in the covalency of the network. The results of the X-ray absorption experiments show the absence of a clear reduction of In{sup 3+} and the incorporation of incoming electrons into the delocalized band structure. Analysis of the discharge curve shows the presence of two different domains. For the first one there is a small interaction between inserted ions. The second one shows a repulsive interaction and a decrease in the diffusion coefficient.

Three thiospinel phases of the In2S3−SnS−SnS2 system solid solution domain have been selected for electrochemical lithium insertion and local investigation by means of 119Sn Mossbauer spectroscopy. Two distinct insertion mechanisms, characterized by two plateaus, are evident from the obtained discharge curves. Mossbauer spectroscopy and X-ray diffraction results are consistent with this. The first insertion mechanism is characterized by the reduction of SnIV and a cell expansion while the second one leads to an increased metallic-type Sn/Li interaction and a cell contraction, both accompanied by a migration of indium from tetrahedral to octahedral sites. The evolution of the hyperfine parameters is discussed to characterize the main differences between the three phases in terms of local and global guest−host interactions.

In this study, sulfide based spinel materials of tin and titanium were synthesised (Cu 2 FeTi 3 S 8 and Cu 2 FeSn 3 S 8 ). A topotactic substitution of tin by titanium atoms was performed in order to obtain electrode materials with high specific capacity associated to a good conductivity. According to the first electrochemical tests the Cu 2 FeTi 3 S 8 spinel appears as a possible anodic material for the Rocking-Chair batteries.

We present the characterization and the electrochemical study of the cation deficient thiospinel Cu3.31GeFe4Sn12S32 as a cathodic material in lithium cells. The pristine compound has a spinel-related structure, where the copper defect in the tetrahedral site induces a partial oxidation of FeII to FeIII. The discharge curve shows the presence of several insertion steps. The reduction of FeIII to FeII and a copper extraction takes place during the first and second steps, respectively. Moreover, the lithium insertion originates a first-order spinel to rocksalt transition, indicated by the third step of the discharge curve. Finally, at low voltages (

We present a combined 57 Fe Mossbauer/X-ray diffraction (Rietveld analysis) study carried out on an In 16 Fe 8 S 32 spinel before and after chemical lithium insertion. To accommodate the new inserted cations in the structure, two mechanisms are observed. First, for a low lithium content, a cation migration takes place from the usually occupied 8 a and 16 d sites toward the usually unoccupied 8 b and 16 c sites, with distortion of the sulfur coordination polyhedra. Second, for a high lithium content, when both 16 c and 16 d octahedral sites are occupied, a decrease of the distortion of the polyhedra is observed. During the insertion process, no clear reduction of Fe atoms is observed but there is an increase in the covalent character of the Fe–S bonds.

The tin reduction during lithium insertion in spinel sulfide compounds is investigated. Mossbauer and RMN spectroscopy are combined with tight binding calculations to analyze the reduction mechanism. It is shown that the formal reaction SnIV + 2e- → SnII is involved without an intermediate Sn oxidation state. The following mechanism is proposed: lithium ions create shallow and deep-defect donor states; the trapping of two electrons on the deep one, which exhibits a negative U behavior, induces the reduction of the corresponding tin atom.

The local environment of antimony atoms in vitreous samples of the ternary system Sb{sub 2}S{sub 3}-As{sub 2}S{sub 3}-Tl{sub 2}S is studied by {sup 121}Sb Moessbauer spectroscopy. The results have been interpreted by means of EBV (empirical bond valence) and EBLV (empirical bond length valence) calculations. Variations in isomer shifts are attributed to changes in the environment of antimony atoms. The isomer shift is found to be a very sensitive parameter reflecting variations in the mean coordination number and in the mean Sb-S bond length. The results presented here confirm the random substitution of As by Sb in the binary system As{sub 2}S{sub 3}-Sb{sub 2}S{sub 3} and the competitive effects-breaking of As-S-As bridges by Tl and formation of As-S-Sb bridges-in the ternary system Sb{sub 2}S{sub 3}-As{sub 2}S{sub 3}-Tl{sub 2}S, in agreement with previous XAFS studies.

The chemical environment of Sb atoms in misfit layer sulfides (SbS)pTS2 (T = Nb, Ti and Ta) was examined by using 121Sb Mossbauer spectroscopy (MS) and X-ray photoelectron spectroscopy (XPS). 121Sb Mossbauer spectra exhibited an asymmetric profile that can be interpreted by assuming two different coordination numbers for trivalent Sb ions. However, these data do not give evidence for the presence of a significant Sb atom fraction of valence similar to metallic antimony as reported by X-ray single-crystal structure calculations. Sb 3d peak profiles were found to be highly symmetric and to suggest the presence of a single electronic state for Sb atoms within the SbS lattice. Although the binding energy of Sb 3d electrons in Sb-containing misfit layer sulfides was found to coincide with that in Sb2S3, the Wagner−Auger parameter values are intermediate between those reported for Sb2S3 and metallic Sb.

International audience; Trimetallic Pt/Al2O3SnIn-Cl naphtha-reforming catalysts were prepared via co-precipitation route. Platinum and chlorine were introduced by the incipient wetness technique on the alumina support already doped with about 0.3 %wt of Sn to obtain about 0.3 %wt of Pt and 1.5 %wt of Cl. For the same Pt, Sn and Cl composition, indium loading ranged from 0.06 to 0.6 wt.%. The obtained catalysts were investigated by 119Sn Mössbauer spectroscopy between 95 and 300 K. Two Sn(IV), Sn(II) and Sn(0) environments have been identified and well characterized by their hyperfine parameters. The Lamb-Mössbauer factors have been determined for each environment and found to be 0.53, 0.27 and 0.31 for Sn(IV), Sn(II) and Sn(0) respectively. The addition of indium has been found to favour the formation of PtxSn alloys. 119Sn Mössbauer spectroscopy results show that addition of even small amount of In (0.06 wt.%) leads to the formation of a Pt3Sn alloy. At higher indium loadings, higher amounts of PtxSn alloys of almost equal Pt and Sn atomic concentrations were detected. The increasing formation of PtxSn alloys with higher indium loading is in good correlation with a decrease of catalyst's overall conversion and selectivity to C1 and C3-C4 paraffins and increase of isomerization selectivity.

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.

Spinel compounds with Cu2CoSn2S8 and CuCoSn3S8 stoichiometries were evaluated as the active electrode materials in lithium anode and ‘rocking chair’-type cells. For lithium cells using CuCoSn3S8 cathodes, the current-composition curves obtained by step potential electrochemical spectroscopy revealed a first Co111/Co11 reduction peak during cell discharge at about 1 F mol−1, which is not observed for the Cu2CoSn3S8 composition. Lithium-ion diffusion coefficients were also larger in this interval. The galvanostatic cycling behaviour in the 2–2.5 V potential window leads to little capacity losses after the first cycle when using CuCoSn3S8 electrodes. Three electrodes sulfide/ LiClO4 (PC)/LiCoO2 rocking chair cells using lithium auxiliary electrode were examined by galvanostatic cycling experiments. When the cells are cycled in the 1.5–2.5 V interval, cell capacity (15 mAh g−1) remains basically unaffected between the second and tenth cycles. The presence of SnIV ions in these solids which are suitable for reduction at lower voltages may be of interest as overdischarge protection.

The local environment of metal (arsenic and antimony) atoms in amorphous samples of the ternary system As 2 S 3 Sb 2 S 3 Tl 2 S has been studied by far infrared transmission spectroscopy. Variations in shape and position of observed bands are attributed to changes in the nature of the coordination patterns of the arsenic and antimony atoms. The variations reveal the different influences of the glass forming arsenic sulfide and antimony sulfide and the glass modifying thallium sulfide on the respective host matrices. The results presented here confirm the hypotheses established previously on the basis of studies of this system by EXAFS at the arsenic K-edge and by XAS at the sulfur K- and antimony L III -edges.

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.

Cu4In20S32 and In16Sn4S32 spinel compounds are used as cathode material in Li/LiClO4(PC)/sulphide cells. For both compounds, incremental capacity vs. voltage curves and diffusion coefficients vs. composition curves showed two consecutive steps of intercalation. The first step occurs between x = 0 and x = 8 for both compositions and at a higher voltage for the tin compound. For larger x values an extended plateau is observed in the voltage vs. composition curves. Cation redistribution is observed during the first insertion step leading to a displacement of In ions from either 8a or 16d sites to another set of octahedral 16c sites in the Fd3m space group. This process is more marked in the copper compound owing to the absence of tetrahedral vacancies in the pristine phase and conditions a lower diffusivity of lithium ions.

The control of the atomic-scale properties of highly dispersed multimetallic particles represents a challenging question for the optimal use of metallic active centers in nanoscience. In particular, improving the formation of PtxSn alloyed clusters on γ-alumina of a size close to 1 nm with a high Sn0/Pt ratio represents a crucial step toward more selective heterogeneous catalysts. For that purpose, bimetallic SnPt-based and trimetallic SnPtIn-based catalysts were prepared by surface organostannic chemistry on monometallic Pt and bimetallic PtIn-based catalysts. These systems were characterized by a multitechnique approach combining CO chemisorption, temperature programmed reduction, scanning transmission electron microscopy, Mossbauer spectroscopy, and X-ray absorption spectroscopy. The nature of the PtSn phase in trimetallic SnPtIn-based catalysts is found to strongly depend on the way indium is initially introduced in the parent catalyst, by either wet impregnation or coprecipitation with aluminum precu...

Thermal, electrical, and optical properties of glass compositions situated along the "As2Se5"-Ag2Se (region I), AsSe-Ag2Se, and AsSe-Ag (region II) lines are investigated and compared. For glass compositions of region I, the glass transition temperature (Tg) and the electrical conductivity (σ) are weak (Tg = 375 ± 5 K and σ = 2,6 × 10-7 cm-1 at 294 K for a 20% concentration of silver). For glass compositions of region II, Tg and σ are higher (Tg = 420 ± 5K and σ = 8,1 × 10-6Ω;-1cm-1 at 298 K for a 20% concentration of silver). All the glasses investigated are high-resistivity and wide-gap semiconductors since their optical gap is higher than 1.4 eV. With increasing Ag content in the glasses, Tg is almost constant, the optical gap decreases slightly but the electrical conductivity increases, and the activation energy decreases.

The three compounds Tl2SnTe5, Tl2SnTe3, and Tl4SnTe3 in the thallium-tin-tellurium system have been isolated. The crystal structure of Tl4SnTe3 is not known. The electronic local order around tin and tellurium has been characterized by means of Mossbauer spectroscopy (119Sn and 125Te). According the crystal structure of Tl2SnTe5 and Tl2SnTe3, the Mossbauer data are discussed in terms of covalent bonding, both tin or tellurium. The crystal structure of Tl2SnTe5 can be described by the chains [Sn2Te(2)2Te(1)8]n. The Te(1) and Te(2) atoms have different behavior. For Tl2SnTe3, the crystal structure can be characterized by [Sn2Te8] and Te atoms behave as tellurium and Te(1) of Tl2SnTe5. For these two compounds, Sn atoms are as Sn α. For Tl4SnTe3, the ionic character of the Sn-Te bond is enhanced and the isomer shifts and quadrupole splittings of 119 Sn and 125Te show the two oxidation state for tin(+2) and tellurium(-2).

Calcium stannate (CaSnO3) and malayaite (CaSnSiO5) were synthesized by means of a high temperature solid-state reaction. Their crystal structures and morphologies were characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy; their electrochemical properties were analyzed by galvanostatic tests. The amorphization of the initial electrode materials was followed by XRD. The first discharge of the oxides CaSnO3 and CaSnSiO5 shows a plateau at low potential, which is due to the progressive formation of Li–Ca–Sn and/or Li–Sn alloys as shown by 119Sn Mossbauer spectroscopy. The results reveal similar electrochemical mechanisms for CaSnO3 and CaSnSiO5 but they completely differ from those related to SnO2.