Effect of composition and crystallization temperature on microstructure ofY- and Er-SiAlONIw-phase glass-ceramics

Glass-ceramics mere produced from Y- and Er-SiAlON compositions containing the I-w phase as the only detectable crystalline phase. TEM analysis showed that these materials had fine-scale glass ceramic microstructures with cry stallite sizes <1 mum and glass contents between 20% and 40%, depending on the starting powder composition: Increased yttrium or erbium content of the starting material resulted in a reduced glass content. The I-w-phase cryst als in all specimens were found by EDX analysis in TEM to display a solid-s olution range with a clear anticorrelation between the yttrium or erbium co ntent and the silicon content: A possible explanation for this effect was s uggested. The average crystal composition approximated a cation ratio of Y: Si:Al = 3:2:1. The composition of the residual glass was also similar in al l specimens. Some small silicon-rich amorphous features were found in the m icrostructures, and it was believed that these had occurred because of phas e separation in the glass during the crystallization process.