The crystal structure of Y3Si5N9O and revision of the compositions of some high nitrogen-containing M–Si–O–N (M = Y, La) phases

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.