Although Y₅(SiO₄)₃N ocurs as an auxiliary phase in Si₃N₄ ceramics as a host for sinter additives such as Y₂O₃, it's structure was hitherto not described in detail. For synthesis a mixture of Si₃N₄, SiO₂ and Y₂O₃ powders with the nominal composition was heated to 1600°C under flowing nitrogen gas in a graphite furnace and reground and reheated three times.

The resulting product was investigated by CuKa₁-X-ray diffraction on a STOE-Stadi-P powder diffractometer in transmission geometry. Qualitative analysis yielded a mixture of 3 phases: a) Y₂SiO₅, sp.gr. I2/a, /1/, b) cuspidine-type Y₄Si₂O₇N₂, sp.gr.P2₁/c, /2/ and c) the title compound Y₅(SiO₄)₃N (PDF 33-1459). The presence of two impurities with large monoclinic unit cells complicated the analysis, yet a 2-phase Rietveld refinement of the known structures of phase a) and b) allowed to separate the reflections of phase c). Indexing yielded the known hexagonal unit cell and cell dimensions of a=9.3671(5)Å and c=6.7727(3)Å. Integrated intensities of this phase were extracted by adding a LeBail refinement of phase c) to the Rietveld refinements of phases a) and b). Subsequent introduction of this information into the real space ab-initio structure determination program Endeavour produced an apatite-related structure of Y₅(SiO₄)₃N with space group P6₃/m (R-factor=4.6%, cost function=0.4586).

Final 3-phase Rietveld refinement of these X-ray data and of former neutron data /3/ obtained on instrument D1A at ILL will be compared and combined.

/1/ B.A.Maximov, V.V.Ilyukin, Y.A Kharitonov, N.V.Belov, Kristallografiya 15 (1970) 926

/2/ K.J.D.MaxKenzie, G.J.Gainsford, M.Y.Ryan, J.Eur.Ceram.Soc. 16 (1996) 553-560

/3/ W.W.Schmahl, M.Györfi, K.G.Nickel, A.Hewat, ECM 18 (1998) 288

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