Synthesis and characterization of chloroborosilicate glasses in the K2O–BaO–Al2O3–B2O3–SiO2–BaCl2 system

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Generally borosilicate glasses are rarely used in photonic applications. Here we modified borosilicate glass by incorporating BaCl2 with a view to their application in the area of photonics. Chloroborosilicate glasses in the system with general composition (mol%) (100−x)(42SiO2–30B2O3–20BaO–4K2O–4Al2O3)–xBaCl2 (where x=0–30) were prepared by the melt quench technique. All the glasses were found to be X-ray amorphous and transparent. They were characterized by X-ray diffraction, infrared and UV–vis-NIR spectral analyses, differential scanning calorimetry, dilatometry, refractive index, dielectric constant measurements, etc. Their glass transition temperature (Tg), coefficient of thermal expansion (CTE), refractive index and dielectric constant have been found to vary in the ranges 614–641°C, 73–91×10−7K−1, 1.58–1.63 and 9.79–11.73 respectively. All the properties are found to be controlled by BaCl2 content. Their covalent character, metallization criterion and Abbe number were found to decrease with increasing BaCl2 content whereas the molar volume, average molar refraction and electronic polarizability increase with increasing BaCl2 content. The devitrified materials have been characterized by XRD which manifests the presence of BaCl2 nanocrystals of sizes 15–30nm. Thus these glasses have the potential to develop BaCl2 nanocrystal containing low phonon energy (~350cm−1) glass-ceramics and are promising for different photonic applications.