Showing papers by "Alain Levasseur published in 1992"

Structural Hypotheses And Raman-Spectroscopy Investigations Of Glasses Belonging To The B2s3-Li2s-Lii System

Abstract: A previous B-11 nuclear magnetic resonance investigation of glasses belonging to the B2S3-Li2S-LiI system had allowed the authors to determine the variation of the number of three and four coordinated boron atoms with composition. These results, in addition to the observation that vitreous B2S3 quite easily forms fibres during casting, have led us to propose structural hypotheses for B2S3 based glasses, which are supported by the present Raman spectroscopy study. For vitreous B2S3 the spectra were accounted for on the basis of the various types of BS3/2 triangles proposed by the model. Molecular orbital considerations allowed us to assign the most significant lines for the binary glasses by assuming that BS3/2 triangles (with or without nonbridging sulphur atoms) and BS4 tetrahedra were present. In the ternary system, lithium iodide has been found to interact slightly on the structural entities, altering their vibrational characteristics without fundamentally modifying their nature.

On the behavior of interactlation compounds in solid state batteries

Abstract: Solid state (Li/B 2 S 3 -Li 2 S-LiI glass/interaction compound) cells were constructed using an isostatic pressing process. Their discharge is compared with that of corresponding liquid electrolyte cells (LiClO 4 -PC). V 6 O 13 , TiS 2 , LiW 3 O 9 F and a-MoS 3 were utilized, showing that the interacalation compound must present multi-directional diffusion for lithium as well as no volume change upon intercalation in order to achieve comparable discharge characteristics for solid and liquid electrolyte cells.

Electron paramagnetic resonance of x-irradiated lithium thioborate glasses

Abstract: X-ray irradiated samples of B 2 S 3 glass and B 2 S 3 -Li 2 S glasses were studied by electron paramagnetic resonance in the X band (9-5 GHz). Analyses of the spectra were carried out by computer simulations specifically adapted for glasses in which distributions of electron paramagnetic resonance parameters are found. In the B 2 S 3 glass an unresolved hyperfine structure was recognised and attributed to an unpaired electron interacting with a boron nucleus

Ionic conduction in B 2 S 3 -Li 2 S-LiI glasses

Abstract: The influence of the addition of the LiI "doping" salt to glasses with general composition (1-y)[(1-x)B2S3.xLi2 S]yLiI (x=0, and 0.5×0.75) is studied, knowing that LiI does not affect the nature of the structural entities present in the base binary glasses. The glass transition temperature decreases when y increases. This effect is smaller for the largest values of x for which the structural entities are smaller and possess more non-bridging sulfurs. The density increases with y, which leads to a slight decrease in the Li+ concentration and to a rather constant Li-Li distance. Whatever the Li2S amount, the conductivity activation energy goes through a weak but definite minimum upon addition of LiI and corresponding break is observed in the pre-exponential factor, which is not predicted by the Anderson-Stuart model. However, it is suggested that this model does not apply to the present glasses, which are rather highly modified. The conductivity data are interpreted by considering two different composition regimes based on the LiI concentration. Isolated I- ions are present at low concentrations, which leads to a decrease in the Coulombic part of the activation energy through the replacement of smaller S- ions by larger I- ones. At higher concentrations, LiI aggregates start to form, which constitute high-barrier regions thus leading to an overall increase in the activation energy.

Paramagnetic centers in lithium thioborate glasses

Abstract: Electron paramagnetic resonance spectra have been recorded in the X band (9.5 GHz) for B 2 S 3 , binary B 2 S 3 -nLi 2 S, and ternary B 2 S 3 -nLi 2 S-pLiI (1≤n≤3, p≤3) glasses. An intrinsic signal without hyperfine interactions corresponding to about 10 15 spins cm -3 , has been detected for 1≤n≤3. Its characteristics (lineshape and width, g value of 2-004) are similar whatever the composition