Core-shell structures with metallic silver as nucleation agent of low expansion phases in BaO/SrO/ZnO/SiO2 glasses

The role of silver as a nucleating agent in BaO/SrO/ZnO/SiO2 glasses is studied with a range of microstructure characterization techniques, such as scanning transmission electron microscopy, ultraviolet-visible spectroscopy, and X-ray diffraction. For this purpose, glasses with different silver and antimony concentrations were synthesized. It was found that silver-particle formation depends strongly on the silver concentration but also on the ratio Ag/Sb. A comparison of the measured plasmon resonances with those calculated from Mie theory enables a calculation of the particle size. This size depends on composition and varies depending on the chosen temperature between 11 and 60 nm. The addition of 1.5 mol% of Sb2O3 is necessary to achieve volume crystallization of Ba1-xSrxZn2Si2O7 (LEAZit) in the glass. This is due to the formation of core-shell structures with metallic silver particles in the center and an oxidic shell, which is highly enriched in Sb and Zn. The metallic silver particles surrounded by a shell show a plate-like shape and provoke the growth of LEAZit crystals with low thermal expansion.