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2019
ACL
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T.Skopak, F.Calzavara, Y.Ledemi, F.Célarié, M.Allix, E.Véron, M.Dussauze, T.Cardinal, E.Fargin*, Y.Messaddeq, 'Properties, structure and crystallization study of germano-gallate glasses in the Ga2O3-GeO2-BaO-K2O system', J. Non-Cryst. Solids 514 98-107 (2019) doi:10.1016/j.jnoncrysol.2019.02.028
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.
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