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The structural modifications and redox processes occurring during lithium deintercalation from the quasi-stoichiometric Li0.97(Ni0.70Fe0.15Co0.15)1.03O2 phase were studied by X-ray diffraction and Mossbauer spectroscopy. A solid solution is observed in the whole deintercalation domain (0.08≤x≤0.97); Rietveld refinement of the XRD pattern shows a strong decrease of the M–O bond distance upon lithium deintercalation. The Mossbauer study shows that nickel and iron ions are simultaneously oxidized, a large number of the iron ions being stabilized in the high-spin tetravalent state. Comparison with the data obtained in the Lix(Ni,Fe)O2 system emphasizes the effect of the small cobalt ions on the facility to oxidize iron ions.

A fluorine-doped nanocrystalline tin oxide has been prepared by thermolysis of xerosol derived from a single molecular precursor. A fluorine to tin atomic ratio, as high as 0.14, was estimated from the results of elemental analysis. The oxidation state of Sn and conducting properties were determined by Mossbauer spectroscopy and resistivity measurements. According to the electrochemical experiments, a reversible capacity up to ∼800 mAh/g has been achieved.

Layered Li 1− z (Ni 1− y Fe y /2 Co y /2 ) 1+ z O 2 phases were obtained by high temperature synthesis. A Rietveld characterization of their XRD patterns shows that the presence of cobalt ions leads to a decrease of the amount of 3d cations in the lithium site vs. the Li 1− z (Ni 1− y Fe y ) 1+ z O 2 phases. This result is confirmed by a magnetic properties characterization. A Mossbauer spectroscopy study shows that there are no iron ions in the lithium site and that a very small amount of iron ions occupies a very distorted tetrahedral site. The electrochemical behavior of these materials in lithium batteries was studied. The XRD characterization of the cycled materials shows a very good cycling reversibility without any change in the structure.

Various Li1 − z(Ni1 − yFey)1 + zO2 materials (0

Lithium nickel oxide derivatives are promising positive electrode materials for the next generation of lithium-ion batteries. Partial substitution of certain cations for nickel in this family of oxides significantly modifies their properties and is therefore an attractive route to develop an optimised oxide electrode which satisfies the demanding requirements for rechargeable battery applications. In this paper the interest is focused on the effect of cobalt, iron, aluminium and magnesium for a general discussion of the effect of cationic substitution on the properties based on a review of results mostly obtained in our laboratories. Although iron substitution does not seem interesting for the practical aspect, iron Mossbauer spectroscopy allows very precise characterisations, interesting to understand the general behaviour of this family of materials. We deal with the optimisation of the synthesis conditions in order to obtain the most electrochemically active materials. The relations between the nature of the substituting cation, the presence of foreign cations in the lithium site, the electrochemical behaviour and the redox processes upon electrochemical cycling are discussed in detail. A new view of the relation between this latter point and the cationic distribution formed during the material synthesis is proposed.

Lithium batteries are being intensively studied owing to the considerable challenge they represent for applications. From a fundamental point of view, the shape of the charge/discharge curves gives information on all the structural and physical properties modifications which occur during the intercalation/deintercalation process. Moreover, the electrochemical reaction is a way of synthesising metastable materials which cannot be obtained by classical methods. The ease of monitoring very accurately either the cell voltage (oxidation state of the material) or the number of electrons transferred (lithium content in the material) makes lithium batteries a new very convenient tool for the solid state chemist. Typical examples are presented.

The cathodic materials r-Li 0.8 H 0.2 FeO 2 (ramsdellite-type) and o-Li 0.7 H 0.3 FeO 2 (orthorhombic form) were synthesized in an autoclave by reaction of iron oxohydroxides with lithium ethoxide in anhydrous ethanol. The compositions of the phases were determined both by means of elemental analyses and density measurements. The crystal structures of r-Li 0.8 H 0.2 FeO 2 and o-Li 0.7 H 0.3 FeO 2 were determined by the Rietveld method. The powders were made of homogeneously distributed submicronic needles. Electrochemical tests of the Li 1–x H x FeO 2 /Li systems were carried out along with X-ray diffraction and Mossbauer spectroscopy. The results from all the physical techniques employed taken together showed the instability of Fe 4+ formed during the recharge of the Li 1–x H x FeO 2 materials, forbidding cycling on the Fe 4+ /Fe 3+ electrochemical couple.

Two lithium iron oxides r-Li0.8H0.2FeO2 (ramsdellite-type) and o-Li0.7H0.3FeO2 (orthorhombic structure) have been synthesised by an ion exchange reaction between respectively α-FeOOH and γ-FeOOH, and C2H5OLi at 170 °C and 140 °C. The reaction products were characterised through elemental analyses, infrared spectroscopy, density measurements and X-ray diffraction. The refinement of the powder XRD patterns of r-Li0.8H0.2FeO2 and o-Li0.7H0.3FeO2 has been performed by the Rietveld method and the results show that the products are isostructural to their precursors.

The electrochemical cycling of a hydrated, iron-substituted nickel hydroxide (20 atomic percent of iron substituted for nickel) in a Ni//Cd cell was studied in situ by 57 Fe Mossbauer spectroscopy. The variations of the iron oxidation state (and spin configuration) were followed throughout the discharge and correlated to the changes of the overall distribution of cationic oxidation states, as well as to the structural modifications. The charge starting from an α-phase leads to a pure γ oxyhydroxide containing Ni III , Ni IV , Fe IV , and average valence Fe ions. During the discharge, the evolution of the various cationic populations deduced from the Mossbauer data provides evidence of a γ-type solid solution domain, in which the Ni IV ions are reduced to the trivalent state rather than the iron ions, followed by γ + α biphased domain.

The U2Ni2Sn stannide has been studied by means of neutron powder diffraction and Mossbauer spectroscopy. This compound crystallizes in the tetragonal P4/mbm space group in an ordered version of the U3Si2-type structure and orders antiferromagnetically below TN = 25(1) K. At T = 1.5 K the magnetic structure is collinear with uranium magnetic moment (1.05(5)μB) perpendicular to the tetragonal c-axis. 119Sn Mossbauer spectroscopy at 4.2 K shows that tin atoms see a zero hyperfine field, in agreement with the proposed antiferromagnetic order.

During these last twenty five years a great efforts have been made in the Laboratoire de Chimie du Solide du CNRS in order to develop high oxygen pressure for the stabilization of unusual oxidation state of transition elements. The aims of such research works was to correlate the increase of the Mn+-O bond covalency versus the increase of the oxidation state n+ to the physicochemical properties of resulting oxides [1]. Iridium was an interesting element due to its position (5d) in the Periodic Table. In 1980 Ir(V) (d4) was stabilized in La2LiIrO6 in the perovskite structure [2]. Such a study had underlined the strong value of the spin-orbit coupling associated to Ir(V) [3]. The stabilization of Ir(VI) is interesting from two points of view : (i) its isotropic electronic configuration (d3), (ii) such a high oxidation state could lead to the strongest M-O bond in an oxygen lattice. Selecting, through a specific methodology, the most appropriate local structural and chemical factors and with the hel...

Magnetic and Mossbauer resonance measurements were performed on iron trifluoride thin films. The layers obtained by condensation of the vapour phase on a substrate heated at 600 K consist of microcrystallites having the bulk FeF3 structure embedded in an amorphous matter in which the ferric ions are tetrahedrally coordinated. The [FeF4] tetrahedra are thought to be linked by two corners and form chains with an overall FeF3 composition. The films obtained with a substrate temperature of 300 K show only amorphous features, with a very low spin freezing temperature. The evidence of tetrahedral coordination for more than half of the ferric ions is again correlated with the probable existence of chains of tetrahedra linked by corners. However, in contrast with the former films, the chains of tetrahedra may be bridged by [FeF6] octahedra. Des mesures magnetiques et de resonance Mossbauer ont ete effectuees sur des couches minces de fluorure ferrique. Les echantillons ont ete obtenus par sublimation thermique sous vide. Les films condenses sur un support chauffe a 600 K sont constitues de microcristallites possedant la structure de FeF3 massif, imbriques dans une matrice amorphe dans laquelle les ions ferriques ont une coordinence tetraedrique. Les tetraedres [FeF4] sont vraisemblablement lies par deux sommets de maniere a constituer des chaǐnes de composition globale FeF3. Les couches deposees sur un substrat maintenu a 300 K presentent uniquement un caractere amorphe avec une temperature de gel de spins tres basse. La coordinence tetraedrique est mise en evidence pour plus de la moitie des ions ferriques. Elle est a nouveau correlee a la presence probable de chaǐnes formees de tetraedres lies par des sommets. Ces chaǐnes pourraient ětre, contrairement aux precedentes, pontees par des octaedres [FeF6].

Magnetic and Mossbauer resonance studies were performed on FeF 3 thin films. The films were prepared by sublimation under vacuum. When the substrate temperature T S during the condensation is 600 K the films consist of microcrystallites with the bulk FeF 3 structure which are embedded in an amorphous phase in which the ferric ions are tetrahedrally coordinated. For T S = 300 K the films show only amorphous features, with a very low spin freezing temperature. In contrast with the former films, the chains of tetrahedra may be bridged by [FeF 6 ] octahedra.