Microstructure Evaluation and Impurities in La Containing Silicon Oxynitrides.

Area of Science:

• Materials Science
• Glass Science
• Ceramics

Background:

• Oxynitride glasses remain largely uncommercialized due to inherent impurities.
• Nitrogen-rich lanthanum silicon oxynitride (La-Si-O-N) glasses present unique microstructural challenges.

Purpose of the Study:

• Investigate the microstructure and intrinsic defects in nitrogen-rich La-Si-O-N glasses.
• Identify the sources of opacity and impurities in these advanced glass materials.

Main Methods:

• Glass synthesis via high-temperature heating (1650-1800 °C) of La metal, Si3N4, and SiO2 in a nitrogen atmosphere.
• Microstructural and impurity analysis using optical microscopy, SEM, AFM, and TEM-EELS.
• Quantification of silicide particle content and characterization of elemental silicon formation.

Main Results:

• The synthesized La-Si-O-N glasses contained <2 vol.% spherical metal silicide particles (<1 µm).
• Opacity is attributed to elemental silicon from Si3N4/SiO2 decomposition above ~1600 °C and La-metal silicide intermetallics.
• No clear correlation found between silicide formation and glass composition or preparation temperature.

Conclusions:

• High-temperature reactions during synthesis lead to critical impurities (elemental Si, silicides) in La-Si-O-N glasses.
• These microstructural defects, particularly elemental silicon and silicides, are the primary cause of glass opacity.
• Addressing these impurity-related defects is crucial for the potential commercialization of oxynitride glasses.