An Investigation into the Effects of Composition and BaF2 Content on the Structure and Crystallization Behavior of SiO2-Al2O3-K2O-BaF2 Oxyfluoride Glasses

Nowadays, oxyfluoride glasses have received much attention from photonic researchers as they benefit from the advantages of both oxide and fluoride glasses (low phonon energy in parallel with high mechanical and chemical durability). The purppose of this paper was to study the different glass compositions in SiO2-Al2O3-K2O-BaF2 system and investigate the BaF2 effects on their crystallization behavior and structure. Therefore, various chemical compositions with different amounts of BaF2 (20, 30, and 40mol%) were chosen and melted in alumina crucibles at 1450˚C. The sample could not melt with the lowest percentage of BaF2. On the other hand, the glass composition containing the highest amount of BaF2 was not able to show high transparency due to the phase separation that occurred in it. Finally, the sample with a 30mole ratio of BaF2 was chosen as the optimized sample due to the favorable transparency. XRD patterns showed that the samples were amorphous and it somehow proved the low transparency in the presence of higher amounts of BaF2 arose from phase separation than the unwanted crystallization. According to the DTA results, the crystallization peak of the fluoride phase decreased from 693˚C to 678˚C by increasing the content of BaF2. FT-IR spectra approved the oxyfluoride structure of the glasses. Higher BaF2 content increased the absorption of peaks in FT-IR spectra since it results in a more discontinuous structure. Fluorine loss was higher for the glass containing the highest amount of BaF2 due to the lower amount of Al2O3 in its composition.