Microstructure Evaluation and Impurities in La Containing Silicon Oxynitrides

Abstract

Oxynitride glasses are not yet commercialised primarily due to the impurities present in the network of these glasses. In this work, we investigated the microstructure and instinctive defects in nitrogen rich La-Si-O-N glasses. Glasses were prepared by heating a powder mixture of pure La metal, Si3N4, and SiO2 in a nitrogen atmosphere at 1650–1800 °C. The microstructure and impurities in the glasses were examined by optical microscopy, scanning electron microscopy, atomic force microscopy, and transmission electron microscopy in conjunction with electron energy-loss spectroscopy. Analyses showed that the glasses contain a small amount of spherical metal silicide particles, mostly amorphous or poorly crystalline, and having sizes typically ranging from 1 µm and less. The amount of silicide was estimated to be less than 2 vol. %. There was no systematic relation between silicide formation and glass composition or preparation temperature. The microstructure examination revealed that the opacity of these nitrogen rich glasses is due to the elemental Si arise from the decomposition reaction of silicon nitride and silicon oxide, at a high temperature above ~1600 °C and from the metallic silicide particles formed by the reduction of silicon oxide and silicon nitride at an early stage of reaction to form a silicide intermetallic with the La metal.

Elucidating photoluminescent properties of Eu‐doped Ca–Al–Si–O(–N) glasses and the local structures of Eu ions

“…Although oxynitride glasses exhibit superior mechanical, chemical, and thermal properties compared to their oxide counterparts, their PL properties have not been extensively investigated. 12,13,[17][18][19] Recently, SiO 2 -Al 2 O 3 gels doped with Eu ions were prepared via the sol-gel process and sintered in an ammonia atmosphere, resulting in the formation of Si-Al-O-N:Eu 2+ glasses. 20 The Eu ion environment was controlled by varying the aluminum or nitrogen content, and the luminescence properties of the prepared glasses were investigated.…”

“…However, the utilization of metal/metal hydrides reduced the oxides, such as silica in the melts, leading to the formation of metallic microparticles, including silicides, which resulted in decreased transparency and glass blackening. Although oxynitride glasses exhibit superior mechanical, chemical, and thermal properties compared to their oxide counterparts, their PL properties have not been extensively investigated 12,13,17–19 …”