Abstract

Phase relationships in M₂O₃–SiO₂–Si₃N₄–MN systems (M = Y, Ln (Ln = La–Sm)) are discussed in relation to the compositions and stability of the high nitrogen-containing phases. Application of the carbothermal reduction and nitridation preparative technique and single crystal structure determination have revealed the presence of minor amounts of carbon or oxygen in compounds previously believed to be pure nitrides. Thus, the phases originally reported as Y₆Si₃N₁₀, YSi₃N₅ and Y₂Si₃N₆ are now found to be Y₂Si₄N₆C, Y₆Si₁₁N₂₀O and Y₃Si₅N₉O respectively. The crystal structure of Y₃Si₅N₉O is described and compared with other M–Si–O–N structures; this phase has orthorhombic symmetry with a = 4.9697(6), b = 16.1192(11), c = 10.6277(17) Å; Z = 4; S.G. Pbcm (no. 57); R1 = 0.0307, wR2 = 0.0748.