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

Abstract Mid-infrared transparent germano-gallate glasses (with gallium oxide as main component) have been studied following the composition law (100- x)[48.3GaO 3/2 -32.2GeO 2 -19.5BaO]- x KO 1/2 (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 40.1GaO 3/2 -26.7GeO 2 -16.2BaO-17KO 1/2 glass composition (in cation mol.%, which corresponds to 28Ga 2 O 3 -37GeO 2 -23BaO-12K 2 O 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. Highlights • Addition of K 2 O results in Ga 2 O 3 -GeO 2 -BaO-K 2 O (GGBK) glass network depolymerization • Mid-infrared transparent gallium-rich GGBK glasses possess high Tg (≥ 671 °C). • Gallium-rich GGBK glasses exhibit high thermal stability against crystallization (~200 °C). • Surface crystallization is the limiting factor to fiber drawing from glass preforms. [ABSTRACT FROM AUTHOR]