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Mg–Si–C–N ceramics were synthesized by reactive pyrolysis of poly(ureamethylvinyl)silazane (PUMVS) polymeric precursor filled with Mg metal powder. Pyrolysis of crosslinked polymeric composites with Mg loadings between 10 and 50 wt.% was carried out in argon atmosphere at temperatures up to 1600 °C. The metal–precursor reactions, ceramization and phase evolution were studied using thermogravimetry, infrared spectroscopy, X-ray diffraction, and scanning and transmission electron microscopy. Predominantly X-ray amorphous Mg–Si–C–N materials, containing up to 15 mol% Mg, were obtained at 1000 °C, with a homogeneous distribution of magnesium at a length scale above 100 nm. The incorporation of Mg in the materials proceeds in two steps: (i) conversion of the Mg metal to magnesium compounds and (ii) solid state diffusion, assisted by vapour phase transport, of Mg into the amorphous Si–C–N–H bulk. Mg retention in the materials at temperatures above 900 °C is realized due to the formation of Si–Mg–N bonds. Primary crystallization of SiC is initiated by magnesium induced partitioning of nitrogen in the Mg–Si–C–N materials. Stability of the amorphous Mg–Si–C–N phase and crystallization of MgSiN2at higher pyrolysis temperatures is governed by the free carbon content in the materials and the nitrogen partial pressure in the thermolysis atmosphere. The results indicate the feasibility of synthesizing monolithic MgSiN2-based ceramics through precursor pyrolysis.

Single crystals of the sialon Ce N-phase Ce₃Si_8 − xAl_xN_11 − xO_4 + x  (x ≈ 1.75) were obtained via a novel route, i.e. by first preparing a fully compacted body with phase constitutions far away from thermal dynamic equilibrium by means of a fast densification technique, spark plasma sintering, and then heat treating this compact in a sialon powder bed at 1600 °C in N₂ atmosphere for 24 h. The structure of the Ce N-phase was solved using MoKα single-crystal data and direct methods. It was refined in space group I2/a with a = 15.798(1), b = 4.8939(3), c = 17.990(1) Å, β = 114.816(4)°, V = 1262.4 Å3, to a weighted R(F_obs2) = 6.7% for 977 unique reflections. The isostructural La phase structure was refined with anisotropic thermal parameters for La and N/O atoms using time-of flight neutron powder diffraction data. The structure exhibits three structural kinds of N/O anions: 4/15 of these are N atoms which are triangularly coordinated by 3 Si/Al atoms, 2/15 are tetrahedron free apex O atoms which are in addition bonded to 3 Ce/La atoms while the remaining 9/15 are on sites that are statistically occupied by N and O atoms and which are bonded to 2 tetrahedral Si/Al atoms and 1–2 Ce/La atoms. Comparisons are made with a previous structural proposal deduced from solid state nuclear magnetic resonance spectra.