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)[48.3GaO3/2-32.2GeO2-19.5BaO]-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/cm 3 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.

Response of Various Yb3+-Doped Oxide Glasses to Different Radiation Treatments

“…The germanate glass exhibits three main Raman bands at 500 (H), 780 (I), and 860 cm −1 (J). The first one corresponds to X-O-X vibrations with X = Ge or Ga [32], located in three-or four-membered GeO 4 -ring structures [33]. The band located at 780 and 860 cm −1 are due to Q 2 units for Ge/Ga tetrahedra and to Q 3 units, likely in an annular structure made from [GeO 4 ] and [GaO 4 ] − units, respectively [32,33].…”

Photosensitivity of barium germano-gallate glasses under femtosecond laser direct writing for Mid-IR applications

“…More specifically barium gallo-germanate (BGG) glasses, appear as materials of choice since they are chemically stable, manufacturable by conventional means (meltquenching) and mechanically resistant [3]. Moreover, hydroxyl impurities could be eliminated by a purification method based on halogens, which produce gallo-germanate glasses with improved transparency up to ~6 μm [17].…”

Glass forming regions, structure and properties of lanthanum barium germanate and gallate glasses

“…In the BaO series, regarding the low frequency band, two main spectral variations can be highlighted upon the insertion of barium oxide: (i) a shrink of the Raman band between 400 and 600 cm -1 and (ii) a shift of the maximum intensity from  530 cm -1 down to  510 cm -1 . The Raman peak around  530 cm -1 has already been reported by several authors [26], [36] and assigned to coupled bending and stretching vibrational modes of Ga -O --Ge bridges in which positive cations act as charge compensator and in which (Ga, Ge) tetrahedra are connected with their corners. The shift to lower frequency could indicate a depolymerization of the glass skeleton upon the increase of the barium oxide content.…”

“…The glass network is reported to be formed of 3D tetrahedral sites of oxygenated germanium and gallium in which the alkaline earth and alkali compensate the gallium tetrahedral negative charge. We have previously reported that such compositions tend to lead to strong surface crystallization [26], [27], making difficult the development of waveguiding optical fibers for instance using preform based technologies [24] [25].…”