Investigation of liquid and glass forming regions in rare earth SiAION systems

The aim of the current work was to ascertain the accuracy of published data on glass formation in the M-Si-Al-O-N systems, (M=Y, Rare Earth), and to investigate 250 further compositions in order to map out the glass forming areas in the Janecke prism. The extent of glass formation in M-Si-Al-O-N systems has been reported by many uthors. However, when all published information is considered, it is apparent that there are some discrepancies and inaccuracies. In the current work, all available published information has been reviewed.

All reviewed diagrams have been redrawn on the Janecke prism representation for accurate comparison. Some computer-based tools were developed to assist in visualisation and to allow manipulation of data and generation of geometric representation. New diagrams were generated and show that the extent of glass formation in the Y-Si-Al-O-N, Nd-Si-Al-O-N, La-Si-Al-O-N and Yb-Si-Al-O-N systems are much more extensive than previously regarded, especially in the more Al-rich regions of these glasses.

Quantitative analysis was carried to out calculate the amount of crystalline phase and residual glass in Y-Si-Al-O-N compositions. Ellipsometry was used to measure refractive index and the values obtained were compared with previously published results.

Controlled cooling experiments were carried out to determine the effect of the extent of glass formation in the Y-Si-Al-O-N system. Even at a cooling rate 2 °C/min showed that glass could be formed and this indicates that TTT curves could be established for these M-Si-Al-O-N systems.

A range of different colours was observed among Yb-Si-Al-O-N compositions, which is due to the differences in oxidation state of the Yb ion.