Preparation and crystal structure of a new Sr containing sialon phase Sr2AlxSi12–xN16–xO2+x (x≈2)

Abstract

A nitrogen-rich sialon phase containing Sr or Eu, named the S-phase, has been reported to form in the M′-Si-Al-O-N systems with M′=Sr and Eu. A sample with overall composition Sr ₂ Al _2.5 Si ₁₀ O ₄ N _14.5 hot-pressed at 1800 °C for 2 h contained approximately 85 vol% of the S-phase, and in addition the α- and β-sialon phases and an amorphous phase. Its structure was solved from X-ray synchrotron powder data (λ=1.1608 Å), using direct methods, and was refined by the Rietveld method from 131 reflections in the 2θ range 10-59° to R _F =2.7%, with the assumed composition Sr ₂ Al ₂ Si ₁₀ O ₄ N ₁₄ , space group Imm2, a=8.2788(9), b=9.5757(9), c=4.9158(4) Å, V =389.7 Å ³ . The structure model was confirmed by its electron diffraction pattern and by high-resolution electron microscopy studies. The structure exhibits a tetrahedral network with high connectivity, each tetrahedron sharing corners with seven surrounding tetrahedra, and the Sr atoms, irregularly coordinated by eight O/N atoms, are found in tunnels extending along [001].