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

Abstract

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 Ba_1−xSr_xZn₂Si₂O₇ (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.