J. Olivier-Fourcade

Evolution structurale et nature des liaisons dans la série des composés soufrés du silicium, du germanium, et de l'étain

Resume Les donnees cristallochimiques et structurales de tous les composes sulfures connus du silicium, germanium et etain sont rassemblees dapres les motifs de coordination presentes par ces atomes vis a vis des atomes de soufre. Ces donnees sont par ailleurs discutees en fonction des caracteristiques propres des elements Si, Ge, Sn ainsi quen fonction de la nature et des dimensions des ions metalliques associes. Le caractere des liaisons Xue5f8S et Mue5f8S presentes dans ces composes est egalement analyse et discute.

Chemical bonding and electronic properties in antimony chalcogenides

The lone-pair antimony chalcogenides are investigated. A detailed qualitative classification of their properties is worked out. The authors show that the {sup 121}Sb Moessbauer isomer shift increases with the covalent character of bonds and with the distortion of the local antimony environment. This is quantitatively explained by a tight-binding band-structure calculation. The lone-pair stereochemical activity also weakens with the forbidden band gap while the conductivity and the metallic character of bonds increase.

Mise au point sur le système binaire TlTe et affinement des structures de TlTe et Tl5Te3

The Tlue5f8Te system has been reinvestigated by thermal analysis and X-ray diffraction and the crystal structures of TlTe (R = 0.059) and Tl5Te3 (R = 0.054) have been redetermined. TlTe is tetragonal, space group I4mcm with a = 12.961 (4) A, c = 6.18 (7) A, and Z = 16. Tl5Te3 is tetragonal, space group I4m with a = 8.917 (3) A, c = 12.613 (3) A, and Z = 4. The TlTe structure can be described in terms of chains [Te]n (with short Teue5f8Te atomic distances of 3.026 and 3.085 A) connected by the TlI polyedra coordination. The Tl5Te3 structure is built from TlTe6 layers perpendicular to the c-axis and shows the simultaneous presence of TlI and TlIII. The expanded formula of Tl5Te3 can be written as TlI9TlIIITe6.

Sur le ternaire TlGeTe: Etude structurale de la phase Tl2GeTe5

Abstract Tl 2 GeTe 5 is orthorhombic, space group Cmmm , with cell dimensions a = 11.657 (5), b = 11.657 (5), c = 14.917 (5), AandZ = 8 . The crystal structure was determined by means of direct methods based on three-dimensional X-ray data. Atomic parameters were refined by a least-squares method to a final R value of 0.077 (507 observed reflexions). The structure can be described in terms of layers parallel to the [001] plane and characterized by (Ge 2 Te 6 ) 4− anions and Te 4 clusters.

Etude de l'insertion de lithium dans In16Sn4S32 par RMN (7Li) et spectrométrie Mössbauer (119Sn)

Chemical lithiation was carried out on the spinel structure of In16Sn4S32 with n-butyl lithium at different temperatures (298, 308, and 318 K). The lithium contents of the samples were determined by atomic absorption and structural analyses by 119Sn Mossbauer and 7Li NMR. 119Sn Mossbauer spectra before and after lithium insertion show the redox process. The SnIISnIV ratio has been evaluated and compared with the lithium concentration in order to propose a reaction mechanism. 7Li NMR spectra allow characterization of the Li+ cations in two different sites of the spinel network. The thermal evolution of the linewidth of mobile lithium permits the determination of the jump frequency νs of Li nuclei and the activation energy of their mobility (0,34 eV).

Etude Mössbauer des formes α et β de In16Sn4S32

Abstract 119Sn Mossbauer effect measurements have been performed on the two forms α and β of In16Sn4S32 over the temperature range 78 ≤ T ≤ 300 K. The effective vibrating mass (Meff) calculated from the temperature dependence of the isomer shift (Meff = 130 and 101 amu, respectively) leads to a lattice temperature of 198 and 245 K for the α and β forms. The recoilless fractions f(α, 78 K) = 0.72 and f(β, 78 K) = 0.76 are discussed and compared with those of other tin compounds.

Electronic transfer in spinel chalcogenides:119Sn Mössbauer spectroscopy and7Li N.M.R.

Chemical lithiation was carried out on the spinel structure of In16Sn4S32.119Sn Mössbauer spectra before and after lithium insertion show the oxidoreduction process. The SnII/SnIV ratio has been evaluated and compared with the lithium concentration in order to propose a reaction mechanism.7Li N.M.R. spectra allow characterization of the Li+ cations in two different sites of the spinel network and the investigation of its mobility.

121Sb Mössbauer studies on some antimony III chalcogenides and chalcogenohalides. Application to the structural approach of sulfide glasses

This study concerns antimony chalcogenides and iodochalcogenides isolated in the systems: M12S-Sb2S3 (MI=Li, Tl), Sb2X3-SbI3, SnX-SbI3 (X=S, Se, Te) and Sb Se −Sb Te. The crystal structure determination of these compounds was carried out. As all elements with pair antimony III atoms show varied environments by sulphur and iodine atoms in terms of activity of its 5s2 non-bonding electron. Mössbauer effect of121Sb leads to the determination of the local electron environment and to complete the crystal structure analysis. Evolution of Mössbauer data is related to antimony III environment type, bond lengths and activity of non-bonding electron pair. These results have been used to give a structural approach of glass forming region in the Tl2S-Sb2S3 system.

Electronic structure of unconventional antimony chalcogenides: Theoretical calculations and121Sb Mössbauer spectroscopy

The electronic structure of five antimony compounds is investigated and the Sb Mössbauer isomer shift is calculated. Its value obtained from the full band structure calculation gives a quantitative account for the chemical notion of delocalization of the 5s(Sb) lone pair. A simple molecular description is also derived which relates the lone pair to the Sb local environment.

Chemical transport reactions in the In-Sn-S ternary system: Existence of tin (II) and tin (IV) atoms by Mössbauer effect of119Sn in the isolated compounds

Iodine vapour transport, carried out in the In-Sn-S ternary system leads to single crystals with quite different morphologies: needles, sticks, sheets and polyhedra. The two oxidation states of tin atoms are shown for all these phases by119Sn Mössbauer effect. A varying relative proportion of tin(IV) — tin(II) is observed according to the different crystal forms.