2007-

2003-2006

1999-2002

Rapport d'Activités

Rapport d'Activités

Nouvelles compositions vitreuses dans les sytèmes non-oxydes.

The search for new or optimized glass compositions in non-oxide systems is an important and fundamental research activity at the laboratory. New vitreous compositions with large content of highly polarizable elements were developed in order to obtain high third-order non linearities. Wide vitreous regions were found in the quaternary PbI2 - As2S3 - Sb2S3 - Bi2S3 system. Besides, fluoride glass compositions based on Ba-In-Sr were optimized for optical fibers drawing. Glasses with low crystallization kinetics were found. Sulfide glasses suitable for rare-earth doping were investigated in sulfide systems as well. Those are namely GeGaSbS and GeGaS-CsX (X=halogen).

RMN dans des fluorures nanostructurés et des verres de chalcogénures.

Nanostructured fluoride powders were prepared by high-energy ball milling conditions. To investigate the local structure 19F, 69,71Ga NMR and 57Fe Mössbauer experiments were carried out respectively in GaF3 and FeF3. Isomer and chemical shifts are consistent with the presence of corner shared fluorine octahedrons Moreover, two types of local structural orders are evidenced and attributed to the presence of crystalline grains and disordered grain boundaries. Concerning chalcogenide glasses, some well resolved solid state 77Se NMR spectra are presented in the AsxSe1-x glass family at ambient temperature. They exhibit three different kinds of Se environments. A comparison with the parent crystalline phases permits to assign the lines to Se-Se-Se, Se-Se-As and As-Se-As selenium atom neighborhoods. The measurements of the relative intensities of the lines prove the validity of the intermediate range order structural model known as the "chains crossing model" which is based on AsSe3 pyramids homogeneously distributed among the divalent Se atoms network. In particular, any scenario involving a selenium clustering process is refuted.

Vitrocéramiques infrarouges à base de chalcogénures.

Glasses from the Ga-Ge-Sb-Se system have been chosen as base glass for fabricating infrared transmitting glass ceramics. Two techniques for generating micro-crystals in the base glass have been studied: homogenous nucleation and heterogeneous nucleation by addition of one nucleating agents. The best optical glass ceramic has been obtained by using homogenous nucleation with a relatively low temperature heat treatment. It has approximately the same transmission as the base glass in the 3-5 and 8-12 µm region with however light losses in the 2 µm region. The thermal expansion coefficient is significantly decreased from 155 x 10-7 K-1 for the base glass to 105 x 10-7 K-1 for the best glass ceramic. The average size of micro-crystals in this glass ceramic is less than 0.5 µm. some preliminary tests show also that it is possible to make optical components (lenses) directly by moulded without destroying completely the optical properties. As an example, the transmission at 10 µm is decreased from about 65% for the glass ceramic (with a thickness of 2 mm) before moulding to about 62% after the moulding operation. This is already very interesting and should of course be improved in the future.

Polissage chimique de verres de chalcogénures.

The etching of TAS glasses can be realized by two chemical solutions : the first one, named sulfochromic solution, is elaborated with concentrated sulfuric acid and potassium dichromate. The second one is prepared with concentrated sulfuric acid and hydrogen peroxide. The chemical treatments of TAS glass samples allow to improve the optical quality of the surface. The infrared transmission, before and after chemical operation, remains identical. Thanks to the chemical etching, the cladding of double index fibers can be dissolved, and consequently, such fibers can be used as infrared probes. It has been shown that the detection was more sensitive as the sensor diameter was decreased.

Elaboration de fibres optiques double indice par la méthode de la préforme en tube scellé.

Double index chalcogenide glass fibers, based on tellurium, arsenic and selenium system (named TAS), were elaborated by a new process. This original technique is based on "build-in casting" inside a sealed silica ampoule. The core/clad structure is obtained by using a core composition that is enriched with tellurium. A strict control of the fabrication parameters leads to well defined core/clad diameter ratios, which vary between 0,25 to 0,75 and to good quality core/clad interface. The attenuation measured by the cut-back method is equal to 1,7 dB.m-1 between 6,5 and 9,5 µm.

Spectrométrie infrarouge deportée par fibre optique.

Infrared optical fibers made with chalcogenide glasses are used as evanescent wave chemical sensors. An original design based on a new generation of glass fibres have been tapered to allow remote, sensitive and in situ measurements in the 800-4000 cm-1 spectral range. On one hand, mice liver tissues have been used as test materials and their MIR spectra clearly showed biochemical differences reflecting metabolic alterations. On the other hand, the first pilot scale measurements were successfully achieved using pollutant as test materials. They proved that a TAS glass fiber (Te2As3Se5) permit to accede to the absorption line positions of pollutants like tetrachloroethylene thanks to the large window of transmission of the glass. Moreover, the original design of the fiber enables to detect very weak concentrations of pollutants. Finally, at this time, a coated TAS glass fiber is a good tool to collect some usable infrared spectra in situation close to the real life ones. Nevertheless, the first mechanical test on TAS glass fibers demonstrates that many effort have to be done during the drawing process to improve the resistance of the fibers.

Verres à propriétés optiques non-linéaires du 3ème ordre et du 2ème ordre pour les télécommunications.

Chalcogenide glasses are studied with respect to their third and second order non linear optical properties. Concerning the third order properties, measurements of the non linear refractive index (n2) and non linear absorption (b) are performed both at 1,064 µm and 1,43 µm. The calculation of the figure of merit at 1.43 µm demonstrates the potential utilization of these glasses in the realization of ultra-fast all-optical switches. Non linearities as high as 850 times the non linearity of silica glass can be obtained. The inscription of a second order non linearity is also demonstrated by all optical poling and thermal poling.

Verres de fluorures et de sulfures dopés par des espèces optiquement actives.

Non-conventional glasses are of prime interest for spectroscopic studies of optically active species. In the present research, emphasis is given to rare-earth-ions suitable for applications in telecommunication. Thus, Pr3+, Er3+ or Tm3+ ions are studied in original glasses such as : rare-earth-rich fluorophosphate glasses, fluoroarsenate glasses, tellurium oxyfluoride glasses, as well as in chalcogenide glasses such as Ge-Ga halo-sulfide and Ge-Ga-Sb pure-sulfide glasses.

Verres de phosphate et fibres optiques pour dispositifs d'amplification intégrés aux longueurs d'ondes télécom.

The development of short optical amplifiers is a great challenge for integra- ted optic and the development of an all-optical network. We have developed and fabricated new phosphate glasses which can incorporate high rare-earth ions concentrations. Er3+-doped and Er3+/Yb3+-codoped phosphate single mode fibers have been drawn and characterised, specially in term of amplification performance. A net gain of 5 dB/cm at 1.5 µm has been demonstrated from an Er3+/Yb3+-codoped single mode phosphate glass fiber with a length of 3.6 cm. This kind of performance is very promising in order to develop optical integrated devices.

Guides d'ondes planaires sur verres non conventionnels pour l'amplification optique.

Channel optical waveguides have been demonstrated with ZBLA (57 ZrF4 - 34 BaF2 - 5 LaF3 - 4 AlF3) fluoride glass. They were prepared by ion exchange between fluoride ions in the glass and chloride ions provided by an HCl gas flow. Reverse ion exchange with HF allowed partial burying of the waveguide. Photolithography was used for lateral confinement. The study aims to low-cost, flat-gain response amplifiers for optical telecommunication in the C-band. Internal gain of 1.1 dB/cm was demonstrated at 1.54 mm, with linear pump-power dependence, in a (Er,Ce) co-doped ZBLA waveguide.

Refroidissement induit par laser dans les verres de fluoro-chlorures dopés Yb3+.

Luminescent cooling due to laser-induced anti-Stokes luminescence has been observed in a new fluoro-chloride glass doped with 1 mol % Yb3+ ions. Based on CdF2 - CdCl2 - NaF - BaF2 - BaCl2 - ZnF2, this glass shows a maximum phonon energy of 370 cm-1, which limitates the non-radiative losses. As a matter of fact, the overall efficiency of Anti-Stokes cooling is low, so that high pumping power and quantum efficiencies near unity are needed to observe the phenomenon. At 300 K, the cooling efficiency is close to 2% in this glass. Recording of the waveforms of photothermal deflection signal indicates that cooling occurs for pumping wavelengths greater than 988 nm.

L'oxynitrure de phosphore PON.

Phosphorus oxynitride, PON, is isoelectronic with SiO2 and its chemical analogue. In addition to the ß-cristobalite and a-quartz PON varieties, a third polymorph was discovered in the P-T diagram. The three crystal structures were determined and their high pressure bebaviour studied up to 48 GPa. SiPO3N was synthesized as a solid solution term between a-quartz SiO2 and PON.

Les verres azotés de phosphates.

Nitridation is one of the best ways to improve the chemical resistance of phosphate glasses. The thermal properties and chemical durability of "model" glasses were related to the structural evolution of the glass network during nitrogen/oxygen substitution. 31P MAS NMR shows that PO4, PO3N and PO2N2 tetrahedra coexist within the glass network, with two-coordinated, -N=, and three-coordinated, -N<, nitrogen atoms, bonded to 2 and 3 phosphorus atoms, as shown by N1s XPS.

Précipitation de particules métalliques dans des verres de phosphates azotés. Approche thermochimique.

High-temperature solution calorimetry has been very useful in elucidating the energetics of several (oxy)nitride materials. This methodology has been used to determine the energetics of formation of phosphorus oxynitride PON samples and of a series of LiNaPON oxynitride glasses. The in-situ precipitation of metallic particles from corresponding oxides in LiNaPON glasses has been predicted from high temperature solution calorimetry results and appropriate thermodynamic cycles. These results constitute the first set of energetic data on nitridophosphates.

Cinétique de dévitrification et ordre à moyenne distance dans les verres de métaphosphates.

A comparative study of the NaPO3 glass crystallization has been performed by means of Differential Thermal Analysis (DTA) and X-ray Powder Diffraction (XRD). From the DTA experiments, we have determined the crystallization dominant mechanism, the nucleation rate type curve (time and temperature dependence), and the kinetic parameters of the crystal growth in the case of non-isothermal studies (i.e. the activation energy and the Avrami exponent). Moreover, we have been able to carry out isothermal studies of the crystal growth, by means of X-ray powder diffraction. Data have revealed the presence of another crystalline phase occurring after heat treatments at low temperatures. On the contrary, non-isothermal DTA experiments were not able to put in light the presence of this secondary phase and its consequence on the overall crystallization phenomenon. In addition, structure factor measurements have been performed by neutron scattering on LiPO3 and Na0.5Li0.5PO3 composition in order to check if the low Q position of the first diffraction peak is a characteristic feature of alkali metaphosphate glasses.

Le rôle de l'azote dans la dévitrification de matrices oxyazotées de type LAS.

A comparative DTA study of devitrification for two LAS glass compositions has been performed .The introduction of nitrogen in the anionic network enhances many physical properties of the Li0.6Al0.1Si0.6O1.65 base oxide glass. In order to precise the role of nitrogen, the dominant crystallization mechanism, the temperature and time dependence of nucleation and the kinetic parameters of the crystal growth have been determined. From all these experiments, it can be assumed that: i) Nitrogen is a nucleating agent, promoting a volume glass crystallization, whereas the oxide sample crystallizes from surface toward the center, ii) The oxide glass nucleation is both instantaneous and heterogeneous but it requires one hour to achieve an homogeneous nucleation in the case of the oxynitride composition iii) The growth of the two crystalline phases is controlled by the progression of the liquid-crystal interface in the case of the oxynitride sample and by a diffusion process for the oxide one iiii) Nitrogen enhances the value of the activation energy for crystal growth.

Matériaux pour le nucléaire : verres de SiAlON et composites apatitiques.

The oxynitride silicoapatites Ln10(Si6O22N2)O2 have a versatile structure which allows various substitutions. We have substituted a lanthanide atom or a cation of the first transition serie metal for another lanthanide atom. The local arrangement of the two different cations is ordered. SiAlON glasses are of potential interest for actinides transmutation. In order to describe the modification of their mechanical properties under irradiation, several vitreous compositions have undergone heavy-ions bombardment. Irradiated samples have been annealed at different temperatures and for different durations to link the evolution of irradiation damage with the temperature of the transmutation target.

Nouvelles voies d'accès à des précurseurs de nitruration.

Transition metal (oxy)nitrides form a class of materials with unique physical properties which give them varied applications as high temperature ceramics, magnetic materials, superconductors or catalysts. They are commonly prepared by high temperature conventional processes, but alternative synthetic approaches have also been explored, more recently, which utilize moderate-temperature conditions. Of prime importance is the nature of the precursor, because it may yield new (oxy)nitride phases unattainable by other synthetic routes. A novel promising method to nitride synthesis has been developed using sulfides as starting materials. Fine reactive molybdenum sulfide precursor powders (Sg 200 m2 g-1) have been synthezised in thiocyanate melt. A transposition of the amorphous citrate method have led to extremely divided Ln6WO12 powders. These powders are very reactive when used as ammonolysis precursors compared to those prepared by solid state methods.

Nouveaux oxynitrures de titane à structure anatase: synthèse et étude par diffraction de neutrons.

The synthesis of new low nitrogen content titanium oxynitride phases with TiO2 anatase structure from several titanium based precursors, like the hydroxyoxide TiO(OH)2, has been investigated. Whereas high ammonia flow and nitridation temperature lead to titanium nitride or high nitrogen content oxynitrides TiOxNy with NaCl structure, lower ammonia flow and nitridation temperature are required to obtain these new TiO2-xNy phases with anatase structure. The nitridation process has been studied by in-situ neutron diffraction experiments. n-semiconductor titanium oxynitride thick films have been developed for the selective detection of gaseous components like H2S and NH3.

Etude thermochimique d'(oxy)nitrures par calorimétrie haute température en solution.

High Temperature oxidative calorimetry is a versatile technique for obtaining enthalpies of formation of nitrides and oxynitrides. In this method, the solid phase is dissolved in a molten oxide solvent (sodium molybdate) while oxygen gas is bubbling through the melt. The nitrogen is evolved as N2 and the final state is a dilute solution of dissolved oxides in the solvent. Then a thermochemical cycle may be written to obtain the enthalpy of formation. The energetics of ionic-covalent, covalent and metallic (oxy)nitride phases are discussed to illustrate the methodology.

Synthèse et caractérisation de nouveaux capteurs chimiques de gaz dans les systèmes M-O-N (M = Ga, Ta, V).

New gallium, tantalum or vanadium oxynitride and nitride sensors have been prepared by using innovative chemical or physical routes. Gallium and tantalum oxynitrides, which present a good thermal stability, have been tested in H2S and NH3 detection. Preliminary results have shown an outstanding sensitivity of "GaON" sensors to H2S.

Des oxynitrures comme pigments colorés.

(Oxy)nitride materials have potential as substitutes for commonly used inorganic pigments which are toxic for environment. By thermal nitridation in flowing ammonia of different ternary oxides belonging to the perovskite and fluorite structure-types, a progressive nitrogen/oxygen substitution was shown to be possible. The powder colour changes continuously within large oxynitride solid solution domains, according to a decrease in the band gap energy value which results from the more covalent character introduced by nitrogen.

Nouveaux matériaux anti-UV oxydes et oxynitrures à base de terres rares.

"Second-generation" UV-blocking materials are needed . Using the fluorite-type rare-earth tungstates Ln6WO12 as starting reference compounds, anionic and cationic substitutions were achieved in (Ln,Ln')-(W,Mo)-(O,N) systems, thus delimiting large solid solution domains. The progressive shift of the absorption edge towards lower energy values makes it possible to tune it at the required value of 3.1 eV (400 nm) with in several cases a steep enough slope.

Structures électroniques d'(oxy)nitrures.

In the frame of density functional theory, we have performed electronic structure calculations on various (oxy)nitrides in order to reach a better understanding of the atomic bonds in the crystal structures and to check whether there is a local nitrogen/oxygen order within the anionic network. In addition, those calculations allow us to model the optical band gaps of compounds having strong potential as coloured pigments.

Les verres du système B-O-F : synthèse et caractérisation

A new class of polymeric glasses belonging to the B-O-F system has been synthesized by reaction between B₂O₃ and BF₃ gas in a sealed silica tube being in a temperature gradient condition. The glass formation mechanism which involves a vapor phase transport indicates that the F- concentration in the glass varies with the deposit temperature. The glass transition temperatures Tg are in the range -15°C to 120°C and depend on the F/B ratio. A foaming phenomenon, due to BF₃ bubbles nucleation, is observed when the "BOF" glasses are maintained above Tg.

Les verres du système B-O-F : le modèle structural

A combination of ¹¹B and ¹⁹F NMR studies as well as ion dynamics computer dsimulation was used to establish the structure of vitreous material BO_1.3F_0.4. The structural evolution versus temperature of this new inorganic polymeric glass has been investigated. Above Tg, the formation of BF₃ gas remains trapped in glass. Only, a single type of fluorine atoms takes part in the formation of BF₃ gas.

Verres de fluorophosphates et fluoroarsenates

Vitreous areas in various fluorophosphate and fluoroarsenate rare earth rich systems have been studied. Particularly stable glass compositions have been found and characterized by determination of characteristic temperatures, refractive index, thermal expansion coefficient and density.

Verres de phosphates et de fluorophosphates dopés terres rares

Novel fluorophosphate glasses containing a heavy concentration - up to 36 mol % - of Tb³⁺ ions are studied in terms of optical absorption, emission, and decay times. Up-conversion processes, resulting in green and blue light, are studied in (Yb³⁺, Tb³⁺) codoped glasses. Er³⁺ phosphate glass lasers with high thermal loading capability are presented. High output power of 20 W is achieved in the eye-safe optical domain at 1.54mm.

Les verres azotés de phosphates

Addition of divalent or trivalent cations coupled with substitution of nitrogen for oxygen within the glass network improve significantly the chemical durability of the phosphate glasses. On the other hand, nitrogen gives the glass a reducing character which makes possible the in situ precipitation of metallic particles of Ag an Cu from the corresponding oxides.

Durabilité chimique d'un verre d'oxynitrure dopé au néodyme

The chemical durability of a SiAlON glass highly doped with Nd (53.8 oxide wt %) was investigated experimentally between 90 and 200°C under flow through conditions using deionized water. Dissolution rates were compared to those found for a tholeitic glass, the content in the major network formers, Si and Al, being approximatively the same.

Verres de fluorures et de fluorochlorures pour l'émission à 1,3 µm

Glass formation is investigated in systems based on ZnF₂, SrF₂, and BaF₂, and in mixed-halide systems. For the first series, stable glasses (DT=Tx-Tg=80°C) with broad infrared transparency (up to 9-10 mm) could be obtained. For the second series, glasses with 15-20 mol % chlorides are found to be fairly resistant to moisture, and still show a broad infrared transparency. The phonon energies are significantly lower than for ZBLAN glass. As a result, the 1.3 mm lifetime of Pr³⁺ ions is larger, up to 218 ms at 1/e³ for a 22 % chloride-containing glass to compare with 117 ms for ZBLAN.

Spectroscopie en sélection de sites et dichroïsme circulaire magnétique de verres de fluorures dopés terres rares

Site-selective spectroscopy and stimulated emission experiments were performed in the ⁴F_3/2 -> ⁴I_11/2 laser transition of Nd³⁺ in a Ba-In-Ga-based fluoride glass (BIG). The experiments show the existence of simultaneous laser emission from two distinguishable subsets of Nd³⁺ sites. Magnetic circular dichroism and fluorescence-line narrowing spectra were recorded for a Eu³⁺-doped fluorophosphate glass. A C_2v symmetry can be proposed for the coordination polyhedron around the rare-earth ion.

Photosensibilité des verres de fluorures

Photosensibility of fluoride glasses is explored. Bragg gratings inscriptions have been performed on rare earth doped glasses as well as undoped glasses, with the purpose of identification of the mechanisms which are at the origin of this photosensibility.

Guides d'ondes planaires réalisés par échange F^-/OH^-, OD^- sur verres de fluorures

Anionic exchange has been carried out on vitreous fluoride materials as ZBLA and BIG glasses in which some fluoride ions have been replaced by OH^-or OD^- ions by pyrohydrolysis.The influence of the process parameters has been studied. The diffusion coefficients, concentration profiles and molar extinction coefficients have been calculated. Gradient index structures have been produced on the surface and the guiding configuration has been determined by the m-lines method.

Guides d'ondes planaires réalisés par échange F^-/Cl^- sur verres de fluorures

Guiding structures have been produced on the surface of fluoride glass by ionic exchange between fluoride ions of the substrate and chloride ions from HCl gas. The planar waveguides have been qualified by using analytical tools (SEM, EDS, SIMS) and optical characterizations such as m-lines method.

Réalisation de guides d'ondes confinés par échange anionique

Gradient index structures have been produced on the surface of fluoride glasses by anionic exchange processes. A description of the preparation of channel waveguides on ZBLA and BIG fluoride glasses is presented. The guiding configuration has been determined by m-lignes method and a near field measurement.

Optique intégrée active sur verres de fluorures

Optical properties of Nd³⁺ and Er³⁺ ions in fluoride glass channel waveguides are presented. For Nd³⁺, the lifetime of the ⁴F_3/2 level is 323 ms at 1/e, to be compared with 400 ms in bulk glass. Despite the lower lifetime, optical amplification is demonstrated at 1.047 mm in a 40 mm wide waveguide. An internal gain of 2.7 dB/cm is achieved for an absorbed pump power of 7 mW at 795 nm. For Er³⁺-doped waveguides, the lifetime of the ⁴I_13/2 level is decreased by 30 %, as compared to bulk samples.

Les verres de chalcogénures : synthèse et caractérisation des systèmes BaS-GeS2-ZnS ou CdS

New glasses have been prepared in the systems BaS-GeS₂-ZnS and BaS-GeS₂-CdS. The ternary diagrams have been investigated and glass forming region have been determined. Thermal and optical characteristics have been conducted in order to qualify this new matrix as an optical host for rare earth spectroscopy.

Verres de sulfures pour l'amplification optique à 1,3 µm

Dy³⁺-doped stabilized-GeGaS sulfide glasses are synthesized and characterized. They show very weak crystallization upon heating as compared to standard GeGaS glass. Because of the low phonon energy inherent in sulfide glasses, the 1.3 mm emission of Dy³⁺ ions can be observed. This transition is characterized in terms of emission cross-section, measured and calculated lifetimes.

Absorption dans l'état excité à 1,3 µm dans les verres de fluorures et de sulfures dopés Nd³⁺

Excited-state absorption and emission spectra are recorded from the ⁴F_3/2 level of Nd³⁺ ions in ZBLAN (Zr-Ba-La-Al-Na) and BIG (Ba-In-Ga) fluoride glasses and in GGSC (Ge-Ga-S-Cs-Cl) chlorosulfide glass. Special attention is paid to the 1.3 mm region. The pump-probe technique utilized in this study is able to predict the gain profile as a function wavelength in optical fibers. Gain is expected at wavelengths greater than 1.31 mm with ZBLAN and BIG, and 1.35 mm with GGSC.

Verres de chalcogénures à forte non-linéarité du troisième ordre

Non-linear refractive index of several chalcogenide glasses have been measured by the z-scan method at 1.06 mm, in order to evaluate their capability to be used in telecommunication all optical ultrafast switching devices. Values of non-linear refractive index eight hundred times higher than that of the SiO₂ glass have been obtained.

Fibres optiques en verres TeXAs pour le domaine 3-13 µm

The optical configuration of IR glass optical fibers has been optimized in three directions : 1) Influence of the polymer coating on the mechanical and optical properties of the fiber. 2) Preparation and characterisation of tapered fiber for improving the evanescent wave absorption of the fiber sensors. 3) Chemical polishing of the IR glass on bulk and fibers for controling the diameter.

Capteurs chimiques et thermiques à base de fibres infrarouges TeXAs

The performances of TeXAs glass optical fibers have been improved in two types of optical systems : 1) IR remote spectroscopy based on evanescent wave absorption, has been optimized by tapering of the fiber sensor diameter. 2) The use of a fibered cooled detector has allowed to obtain a better sensitivity in low temperature measurements using IR glass fiber.

Récents développements dans le domaine des verres de chalcogénures

The structure of Te₃X₂ glasses has been studied using Mossbauer spectroscopy. New glasses based upon the GeS₂ and GeSe₂ system have been discovered and investigated. In order to prepare vitroceramics, a nucleation growth study has been performed on Ga-As-Se-I glasses.

Détermination par DSC de courbes de nucléation et de croissance cristalline de verres halogénés

The glass-crystal equilibrium has been studied for two family of halide glasses, fluoride glasses and chalcohalide glasses. The crystallisation process has been followed by determination of nucleation and growth curves from DSC experiments. DSC is shown to be a suitable technique for evaluation of such curves.

Etude de la dévitrification de verres du système Mg-Y-Si-Al-O-N

Non-isothermal kinetic parameters of devitrification for two glasses in the Mg-Y-Si-Al-O-N system were determined by differential thermal analysis. The substitution of oxygen by nitrogen in the anionic network, the cationic one remaining the same, results in a 80 kJ/mol increase of the apparent crystallization activation energy. Furthermore, the determination of the Avrami exponent, whose value is close to 1.5 for each glass, corresponds to a crystal growth probably controlled by a diffusion process

Capacités calorifiques de verres du système Mg-Y-Si-Al-O-N

Heat capacity measurements for two glasses in the Mg-Y-Si-Al-O-N system have been carried out by differential thermal analysis in the range from room temperature to the glass transition. The substitution of oxygen by nitrogen in the anionic network leads to an incrase in the solid heat capacity measured at a constant pressure. Furthermore,, the difference between the Cp values for the solid state and the liquid state is close to 10 kJ per mole conferring to these glasses a fragile feature. The determination of the Debye temperature leads to values from 1073K for the oxide glass to 955K for the oxynitride one, the corresponding Debye frequencies being 746 cm^-1 and 664 cm^-1 respectively.

Nouveaux phosphates cristallisés - N dans PO₄

ß-InPO₄ and In₃P₂O₈ are new phosphates with isolated tetrahedra. The second one is characterized by (In-In)⁴⁺ pairs. Na₃AlP₃O₉N and Na₂Mg₂P₃O₉N are the first terms of two series of nitridophosphates in which the nitrogen atoms form discrete N(PO₃)₃ groups. Cs₃Mg₂P₆O₁₇N is a first example of a nitrido-cyclohexaphosphate with (P₆O₁₇N)^7- independent cycles. K₂MgP₃O₈N and an indium nitrido-sodalite [(P₁₂N₂₄)^12- framework] are other possibilities of the nitrogen substitution in the PO₄ tetrahedra.

L'oxynitrure de phosphore PON

Phosphorus oxynitride, PON, is isoelectronic with SiO₂ and is its chemical analogue. The crystal structures of the two compounds are very similar : PON crystallizes as a ß-cristobalite-type phase which can be transformed under high pressure into an a-quartz-type phase. The high pressure behaviour of the two phases has been studied up to 48 GPa. On the other hand, PON is an interesting material for several application domains, such as passivation of InP, flame retardancy or elaboration of nitridophosphates.

Nouveaux catalyseurs oxynitrures : les métallophosphates azoté

New high surface area metallophosphate oxynitride powders "MPON" (M = Al, Ga, In, Ti, Zr, Cr) have been synthesized by nitridation in flowing ammonia of reactive phosphate precursors prepared using the soft chemistry route, and characterized as novel basic catalysts. In particular, platinum supported gallo-aluminophosphate oxynitrides Pt-AlGaPON are active catalysts for isobutane dehydrogenation.

Une nouvelle famille de composés de grande surface spécifique dans le système Al-V-O-N

High surface area powders of VAlON compounds were prepared by nitridation under ammonia of mixed vanadium and aluminium oxydes obtained by a coprecipitation technique or soft chemistry routes. Control of the vanadium/aluminium ratio is possible, which allows to control over the nitrogen content in the final compound. When the nitridation temperature is 600°C, an amorphous oxinitride of vanadium and aluminium is obtained with a specific area higher than 200m²g^-1 depending on the V/Al ratio.

Préparation d'oxynitrures semi-conducteurs utilisables comme capteurs de gaz

New oxynitride phases, CdGeON and CdZnGeON, have been prepared by reaction of gaseous ammonia on "CdGeO" and "CdZnGeO" amorphous phases. The amorphous oxides are obtained by coprecipitation of Cd²⁺, Zn²⁺ and Ge⁴⁺ by addition of aqueous ammonia at 90°C. The soft chemistry process involved produces powders with controlled morphological characteristics . The oxynitride phases can be used as gas sensors.

Capteurs de gaz à base d'oxynitrures semi-conducteurs

n-semiconductor oxynitride thick films have been developed for selective detection of gaseous components, like NH₃, NO_x, H₂S, SO₂. Sensitivity, selectivity, reversibility and stability of the sensing materials, but also, of the kinetic responses have required an optimal thermal control and packaging for the sensors.

Microcapteurs chimiques à base de CdGeON pourla détection de H₂S. Réalisation d'un prototype industriel

The realisation of a prototype gas sensor for the detection of H₂S based on cadmium germanium oxynitride "CdGeON" has been investigated. The prototypes are designed as thick film devices prepared by the screen-printing technique. The influence of some parameters on the response to H₂S has been studied.

Préparation et caractérisation de matériaux composites à matrice polymère renforcés par des fibres végétales

We present the performances of natural fiber-reinforced composite materials. Flax is the fiber more used in our study because of its mechanical properties and its supplying. The structure and properties of these fibers, the mechanical properties of the composites have been determined. A comparative study with glass-reinforced composites prove the interest of flax fibers for composite materials.

Nouvelles voies d'accès à des nitrures de métaux de transition

A new promising route to make transition metal nitrides consists in the thermal ammonolysis of corresponding sulfides. Mo₅N₆ and d-MoN , W₅N₆ , CrN- and TiN-related phases have been produced from MoS₂ ,WS₂ , Cr₂S₃ and NaCrS₂ , and TiS₂ , respectively. Synthesis of reactive precursor powders with high surface area can be performed in thiocyanate melt. The new nitrides Nb4N5 and LiNb₃N₄ , as well as two different NaCl-type Li-Nb-O-N oxynitride phases have been prepared by nitridation of alkaline niobates.

Application des composés de type nitrure comme pigments colorés

The market of colored pigments has changed for a few years. Actually, pigments based on heavy metals like lead, cadmium, chromium or cobalt are now forbidden in many countries because of environmental problems. So, it seems obvious that new pigments have to be found and that is what we aim at doing in the field of nitride-type compounds.

Une nouvelle classe de composés minéraux oxyazotés : entités N-N dans des matrices oxydes

So called "intermediate phases", associated to a nitrogen retention phenomenon, Mⁿ⁺O_n/2(N_x), appear during thermal oxidation of the oxynitrides into oxides. They have been isolated and characterized for numerous oxynitrides belonging to different structure types. In addition to chemical analysis and X-ray diffraction results, XPS studies have shown an N_1s binding energy near 403 eV, in the same range as organometallic dinitrogen complexes, containing in particular M-NºN-M entities. Moreover, a n_NºN band located at 2320-2340 cm^-1 has been observed by Raman spectroscopy, which clearly proves that the nitrogen atoms are present in the oxide lattice as dinitrogen pairs.

Préparation et frittage de matériaux à clusters de type M_xMo₆X₈ pour la détermination de leurs propriétés thermoélectriques

Some cluster materials M_xMo₆S₈ exhibit thermoelectric properties. In order to study these compounds, it is necessary to prepare well-densified samples which can be obtained only by using hot-pressing technique.

Céramiques oxynitrures SiBON obtenus par nitruration de précurseurs organométalliques

Amorphous SiBON powders have been synthesized by nitridation of polyborosiloxane, a polymer containing Si-O-B linkages, prepared by the condensation reaction between SiCl₄ and (B(OH)₃. Sintering of these powders by hot pressing techniques provides oxynitride ceramics characterized by analytical tools such as XRD, SEM, HREM, EDS, IR spectroscopy and microhardness measurements.

Un exemple de collaboration Recherche-Entreprise : la détermination par diffraction de rayons X de la concentration en silice cristalline dans les poussières industrielles

A X-ray diffraction method has been optimized for the quantitative determination of crystalline phases of silicon dioxide samples. Sample preparation on a silver membrane filter is required. Quantitation is achieved by measuring the diffraction intensity of the analyte and the attenuation of the 111 silver diffraction line due to the deposited sample. The process was optimized for collection and analytical silica determination in industrial dusts.

Mécanique et physico-chimie de la rupture des verres spéciaux et des céramiques

The search for the physico-chemical mechanisms leading to fracture, and the preventive science that could result from the knowledge of these mechanisms, is a huge and open research field, where almost everything remains unexplored. The first stage of investigation consists in the setting of environmentally-controlled stable crack growth testing devices. Then, the coupling between the mechanical resistance of the materials against fracture and the fracture surface chemistry will be studied in detail, as a function of temperature, testing velocity, atmosphere and glass composition.

Nouveaux oxynitrures de type pérovskite ou fluorine dans les systèmes M-Ta(Nb)-O-N (M: alcalinoterreux) et Ln-W-O-N (Ln: élément de terre rare) en vue d'une application comme pigments colorés.

Optimisation des compositions de verres de fluorure

Verres actifs pour guides d'onde micro-laser

Spectroscopie des ions de terres rares dans les verres d'halogénures

Guides d'ondes planaires

Fibres optiques infra-rouges en verres de fluorures BIG et en verres TeX

Optimisation des verres TeX pour la transmission du laser CO₂

Utilisation des fibres optiques en verre TeX pour l'analyse spectroscopique déportée

Verres d'aluminates azotés

Verres azotés de phosphates: oxynitrure PON

Composites particulaires à matrice verre azoté

Composites à matrice verre azoté et renfort fibreux

Propriétés thermiques et thermomécaniques des verres

Nouveaux verres

Equilibre verre-cristal

Matériau expansé

Oxynitrures de structure pérovskite et dérivée

Nouvelles familles d'oxynitrures

Précurseurs organométalliques de matériaux de type nitrure

Nitrures et oxynitrures de métaux de transition pour applications catalytiques

Oxynitrures semi-conducteurs comme capteurs de gaz

Catalyseurs basiques à base d'aluminophosphates azotés "AlPON"

Céramiques structurales azotées