Peculiarities of Ga and Te incorporation in glassy arsenic selenides

International audienceEffect of simultaneous Ga and Te addition on the structure of As2Se3 glasses is studied using X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure (EXAFS) and Raman techniques. It is shown that most of As, Se and Te atoms build a covalent network according to their main valences. Three-fold coordinated As atoms form pyramidal structural units, which are connected via bridges of two-fold coordinated chalcogen atoms (Se, Te). On the other hand, coordination of Ga in glassy samples is found to be greater than three, as expected from its valence, increasing with Te content. Some of the As atoms appear to be converted into four-fold coordinated state at low Te concentration, while a fraction of Te and, possibly, Se atoms are thought to exist in a singly-coordinated (terminal) state in the vicinity of Ga in the samples with higher Te concentration

Metastability effects on low-phonon energy chalcogenide glasses

Les verres de chalcogénures sont développés en raison de leurs propriétés de transparences dans l'infrarouge. Il est par exemple possible de fabriquer des fibres optiques pour des fonctions capteurs fonctionnant dans le moyen infrarouge. L'objet de la présente thèse consiste à étudier le comportement métastable des verres de chalcogénures lorsqu'ils sont soumis à des contraintes particulières : thermiques, rayon γ, ajout d'élément déstabilisant. Des compositions dopées par des terres rares ont également étudiées pour développer des sources fonctionnant dans le moyen IR.Chalcogenide glasses are developed because of their properties of transparency in the infrared. For example it is possible to manufacture optical fiber or planar wavguide for sensing in the mid-infrared. The purpose of this thesis is to study the metastable behavior of chalcogenide glasses when subjected to specific constraints: thermal behavior, γ ray irradiation, addition of destabilizing elements. Compositions doped with rare-earth have also been also studied in order to develop sources operating in the mid-infrared range

Effect of Rare-Earth Doping on Free-Volume Nanostructure of Ga-Codoped Glassy (As/Sb)2Se3

International audienceSubsequent stages of atomic-deficient nanostructurization finalizing rare-earth functionality under Pr-doping in Ga(AsSbSe) glass are studied employing method of positron annihilation lifetime spectroscopy. Genesis of free-volume positron trapping sites, composed of atomic-accessible geometrical holes (void cores) arrested by surrounding atomic-inaccessible Se-based bond-free solid angles (void shells), are disclosed for parent AsSe, Ga-codoped Ga(AsSe), as well as Ga-codoped and Sb-modified Ga(AsSbSe) glasses. The finalizing nanostructurization due to Pr-doping (500 wppm) in glassy Ga(AsSbSe) is explained in terms of competitive contribution of changed occupancy sites available for both rare-earth ions and positrons

Effect of high-energy mechanical milling on the medium-range ordering in glassy As-Se

International audienceEffect of high-energy mechanical milling on glassy AsxSe100 - x (5 <= x <= 75) is recognized with X-ray powder diffraction analysis applied to their diffuse halos ascribed to intermediate-and extended-range structural ordering, which are revealed respectively in the first sharp diffraction peak (FSDP) and principal diffraction peak (PDP). Straightforward interpretation of the results is developed within modified microcrystalline approach, treating diffuse halos as superposition of broadened Bragg-diffraction reflexes from remnants of inter-planar correlations, supplemented by inter-atomic Ehrenfest-diffraction reflexes from most prominent inter-atomic and inter-molecular correlations between cage-like molecules (such As4Se4 and/or As4Se3). Milling is shown to be ineffective in glassy arsenoselenides near Se (x < 20), while causing increase in the FSDP width for glasses with 20 <= x <= 40 due to destroyed inter-planar ordering. Remnants of cage-like molecules in over-stoichiometric As-rich AsxSe100 - x glasses (40 <= x <= 75) disappear under milling, promoting formation of higher polymerized structural network. This milling-driven reamorphization results in a drastic increase in the FSDP position and fragmentation impact on the correlation length of the FSDP-responsible entities. Breakdown in intermediate-range ordering in these glasses is accompanied by changes in their extended-range ordering revealed in high-angular shift and broadening of the PDP. This effect is concomitant with the disappearance of distant inter-atomic correlations between quasi-crystalline planes in the milled arsenoselenide glasses at a cost of prolonged correlations dominating in their extended-range ordering

The influence of Sb on glass-forming ability of Ga-containing As2Se3 glasses

International audienceEffect of As to Sb substitution on glass-forming ability of As2Se3 glass under Ga additions was comprehensively studied using optical spectroscopy in visible and IR regions, differential scanning calorimetry, X-ray diffraction as well as Raman scattering techniques. The crystallization processes enhanced by Ga additions to As2Se3 glass were significantly suppressed under such As to Sb substitution. Following conventional synthesis, it was possible to substitute up to 50% of As by Sb within Ga-y(As0.40-xSbxSe0.60)(100-y) cut-section without essential impact on glassy state, thus improving optical properties in the IR region by lowering the phonon energy. In the case of Ga-y(As0.28Sb0.12Se0.60)(100-y) cut-section, up to 8at.% of Ga can be introduced without crystallization, whereasin case of Ga-y(As0.40Se0.60)(100-y) system, glass-forming ability is limited just up to 3at.% of Ga. The prepared Ga-5(As0.28Sb0.12Se0.60)(95) glass composition was shown to be the richest in Ga keeping its vitreous state, good optical and thermodynamic properties allowing further rare-earth doping and fiber drawing

Tailoring Se-rich glassy arsenoselenides employing the nanomilling platform

International audienceBy XRPD analysis related to diffuse peak-halos in Se-rich glassy AsxSe100-x, the high-energy nanomilling driven reamorphization in these substances is recognized as molecular-to-network transformations of Se chains bridging cation polyhedrons (like AsSe3/2 pyramids) from preferential cis- to trans-configurated topology. At the medium-range structure, the process of reamorphization is revealed as enhancement in the intermediate-range ordering of these glasses due to high-angular shifted and broadened first sharp diffraction peak (FSDP) accompanied by suppression in extended-range ordering due to high-angular shifted but narrowed principal diffraction peak (PDP), so that peak-halos become more distinguishable after nanomilling. Principal trend in the XRPD patterns of glassy arsenoselenides with growing Se content is revealed as suppression in intermediate-range ordering accompanied by enhancement in extended-range ordering, resulting in more overlapped peak-halos. Irregular sequence of randomly distributed cis- and trans-configurated linkages in Se-rich g-AsxSe100-x is visualized by ab initio quantum-chemical modeling of molecular and chain-like network clusters

Positron annihilation probing of crystallization effects in TAS-​235 glass affected by Ga additions

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