SUPERMAT – A virtual center for sustainable development of advanced materials operating under extreme conditions

The expertise, main experimental facilities and some selected results of the EU SUPERMAT Consortium are described, showing the importance of integrating modelling and simulation, fast sintering and coating technologies and specific characterisation techniques for obtaining high temperature ceramics, oxide dispersion strengthened (ODS) steels or Li-ion batteries with controlled properties for extreme environmental applications

Structure-properties relationship study in niobium oxide containing GaO3/2-LaO3/2-KO1/2 gallate glasses

The investigation has been devoted to the effect of the KNbO3 in a gallate based glasses of composition (100-x) (69GaO3/2-11LaO3/2-20KO1/2) – x KNbO3 with x varying from 0 to 20 mol.% allowing the use of standard melt technique. The thermal and optical properties were characterized and the local structure has been investigated by Raman spectroscopy. The gallium ions are mostly found in tetrahedra thanks to charge balancing of potassium and lanthanum ions. The continuous increase of the KNbO3 concentration gives rise to the progressive formation of a niobate subnetwork composed of corner shared NbO6 octahedra which does not depolymerize the gallate glass network. This addition has a limited impact on the multiphonon edge in the infrared while it causes a significant increase of the refractive index. For KNbO3 concentrations above 14 mol.% a phase separation occurs due to the absence of formation of a mixed gallo-niobate glass skeleton.Initiative d'excellence de l'Université de Bordeau

Structure-properties relationship study in niobium oxide containing GaO3/2-LaO3/2-KO1/2 gallate glasses

The investigation has been devoted to the effect of the KNbO3 in a gallate based glasses of composition (100-x) (69GaO3/2-11LaO3/2-20KO1/2) – x KNbO3 with x varying from 0 to 20 mol.% allowing the use of standard melt technique. The thermal and optical properties were characterized and the local structure has been investigated by Raman spectroscopy. The gallium ions are mostly found in tetrahedra thanks to charge balancing of potassium and lanthanum ions. The continuous increase of the KNbO3 concentration gives rise to the progressive formation of a niobate subnetwork composed of corner shared NbO6 octahedra which does not depolymerize the gallate glass network. This addition has a limited impact on the multiphonon edge in the infrared while it causes a significant increase of the refractive index. For KNbO3 concentrations above 14 mol.% a phase separation occurs due to the absence of formation of a mixed gallo-niobate glass skeleton.Initiative d'excellence de l'Université de Bordeau

Effect of potassium or yttrium introduction in Yb3+-doped germano-gallate glasses on the structural, luminescence properties and fiber processing

International audienceHere we report on the effect of potassium or yttrium on the luminescence spectroscopic properties of Yb 3+-doped germano-gallate glasses as well as the ability to shape them into optical fibers with the objective of using such glasses to produce near-infrared optical gain medium. Two ytterbium-doped germano-gallate glass systems, (100-x) (28Ga 2 O 3-37GeO 2-23BaO-12K 2 O)-xYb 2 O 3 (x = 0, 0.5 and 3 mol.%) and 29.6Ga 2 O 3-39.1GeO 2-24.3BaO-7 (yY 2 O 3-zYb 2 O 3) (y = 6.5, 4, 0 and z = 0.5, 3, 7 mol% respectively) have been prepared and the systematic investigation of their thermal, structural, optical and spectroscopic properties have been carried out. The increase in ytterbium oxide content leads to an increase of the glass transition temperature, crystallization temperature and the density of the glasses, as well as induces a red-shift of the cutoff wavelength. Raman spectroscopy analysis shows that both ytterbium oxide addition and potassium substitution by yttrium modify the 3D interconnected germano-gallate glass network. Lifetime diminishes with the increase of Yb 3+ concentration but remains higher in the yttrium-containing glasses. We demonstrate that the production of crystal-free light guiding fibers via the preform-to-fiber approach becomes possible only in the yttrium-containing glass system. Cutback optical attenuation measurements of the produced fibers show minimum losses of 3.3 dB/m at 1310 nm

Structure and properties of gallium-rich sodium germano-gallate glasses

Glass compositions in the gallium-rich region of the ternary GaO3/2–GeO2–NaO1/2 vitreous system are studied as a function of the Na/Ga cationic ratio (ranging from 1.30 to 1.61) for a fixed GeO2 content. Glass structures are investigated by 71Ga magic angle spinning nuclear magnetic resonance, infrared, and Raman spectroscopies, and the thermal, optical, and physical properties are characterized. Vibrational spectra are interpreted with the help of density functional theory calculations. Gallium oxide generally enters the germania network in fourfold coordination, however, for a Na/Ga ratio below unity, gallium cations tend to charge balance with the formation of five- or six-fold coordination units. When the amount of sodium is greater than gallium, nonbridging oxygens are formed preferably on germanate tetrahedral units. These structural descriptions are used to understand the evolution of glass properties such as glass transition temperature, density, and refractive index.Initiative d'excellence de l'Université de BordeauxImPRession laser de fibres exOtiques Multi-MaTEriau

Extended germano-gallate fiber drawing domain: from germanates to gallates optical fibers

Here we report on the production of crystal-free light guiding fibers using a preform-to-fiber approach in the germano-gallate glass system Ga2O3-GeO2-BaO-La2O3-Y2O3 for various contents of gallium to germanium. For glasses in the system Ga2O3-GeO2-BaO-K2O, where surface crystallization precludes fiber drawing from the preform, an open-crucible technique enables the drawing of fiber samples tens of meters long. Cut-back optical attenuation measurements show the extended transmission in the mid-infrared of the produced fibers, up to 2.8 µm with minimum losses of 3.1 dB/m at 1310 nm from unpurified glass. These results show that the germano-gallate glasses represent promising mid-infrared materials over an extended fiber drawing domain.Initiative d'excellence de l'Université de BordeauxImPRession laser de fibres exOtiques Multi-MaTEriau

Properties, structure and crystallization study of germano-gallate glasses in the Ga2O3-GeO2-BaO-K2O system

Mid-infrared transparent germano-gallate glasses (with gallium oxide as main component) have been studied following the composition law (100-x)[48.3GaO3/2-32.2GeO2-19.5BaO]-xKO1/2 (with x = 0, 5, 10, 13, 17 mol%). All prepared glasses are transparent from approximately 280 nm up to 5.5 μm, with a measured linear refractive index and density decreasing respectively from 1.72 to 1.67 (at 1538 nm) and 4.79 to 4.34 g/cm3 with increasing potassium oxide content. As expected, the increase of potassium oxide content also results in a decrease of the glass transition temperature (698 to 671 °C) and the viscosity in the softening regime whereas the thermal expansion coefficient increases (4.8 to 10.3 × 10−6 K−1). These results are related to the depolymerization of the 3D interconnected glass network which has been studied by Raman spectroscopy. Large thermal stability criteria (difference between onset of crystallization and glass transition temperatures) ranging from 182 to 199 °C have been measured by DSC for the compositions containing potassium oxide, suggesting strong potential for fiber drawing from glass preforms. The 40.1GaO3/2-26.7GeO2-16.2BaO-17KO1/2 glass composition (in cation mol.%, which corresponds to 28Ga2O3-37GeO2-23BaO-12K2O in mol.%) was then selected for further investigation. Its mechanical properties (Young and shear moduli, Poisson's ratio, hardness) were measured, showing values close to those reported for well-known barium gallo-germanate (BGG) glasses. A thorough crystallization study was then carried out using DSC (Marotta's method), X-Ray diffraction and electron microscopies (TEM and SEM) to better understand the unexpected surface crystallization issues observed during the glass preform fiber drawing process. The potential of using such germano-gallate glasses to produce mid-infrared optical fiber of high mechanical strength is discussed.Initiative d'excellence de l'Université de BordeauxImPRession laser de fibres exOtiques Multi-MaTEriau

Properties, structure and crystallization study of germano-gallate glasses in the Ga2O3-GeO2-BaO-K2O system

Mid-infrared transparent germano-gallate glasses (with gallium oxide as main component) have been studied following the composition law (100-x)[48.3GaO3/2-32.2GeO2-19.5BaO]-xKO1/2 (with x = 0, 5, 10, 13, 17 mol%). All prepared glasses are transparent from approximately 280 nm up to 5.5 μm, with a measured linear refractive index and density decreasing respectively from 1.72 to 1.67 (at 1538 nm) and 4.79 to 4.34 g/cm3 with increasing potassium oxide content. As expected, the increase of potassium oxide content also results in a decrease of the glass transition temperature (698 to 671 °C) and the viscosity in the softening regime whereas the thermal expansion coefficient increases (4.8 to 10.3 × 10−6 K−1). These results are related to the depolymerization of the 3D interconnected glass network which has been studied by Raman spectroscopy. Large thermal stability criteria (difference between onset of crystallization and glass transition temperatures) ranging from 182 to 199 °C have been measured by DSC for the compositions containing potassium oxide, suggesting strong potential for fiber drawing from glass preforms. The 40.1GaO3/2-26.7GeO2-16.2BaO-17KO1/2 glass composition (in cation mol.%, which corresponds to 28Ga2O3-37GeO2-23BaO-12K2O in mol.%) was then selected for further investigation. Its mechanical properties (Young and shear moduli, Poisson's ratio, hardness) were measured, showing values close to those reported for well-known barium gallo-germanate (BGG) glasses. A thorough crystallization study was then carried out using DSC (Marotta's method), X-Ray diffraction and electron microscopies (TEM and SEM) to better understand the unexpected surface crystallization issues observed during the glass preform fiber drawing process. The potential of using such germano-gallate glasses to produce mid-infrared optical fiber of high mechanical strength is discussed.Initiative d'excellence de l'Université de BordeauxImPRession laser de fibres exOtiques Multi-MaTEriau