The B-phase solid solution range in yttrium and rare earth sialon systems

Extensive fine probe EDX analysis in a FEG-TEM has shown that the lenticular B-phase crystals in glass-ceramic microstructures formed through the crystallisation of glasses of composition (e/o) 35RE:45Si:20Al:830:17N, where RE stands for erbium, ytterbium, yttrium or a mixture of yttrium and ytterbium, take up a substantial range of composition that is determined by the radius of the RE3+ cation. The element RE is always clearly anti-correlated with the silicon. A larger cation radius moves the B-phase composition range to lower RE contents, and as a consequence of the anti-correlation with silicon, the silicon solid solution range goes to higher values. This is accompanied by only small variations in the aluminium content. The results are discussed in relation to existing models for B-phase structure and solid solution range.