Nitridosilicates, oxonitridosilicates (sions), and oxonitridoaluminosilicates (sialons)

Abstract

The new oxonitridosilicate (sion) Ce₄[Si₄O₄N₆]O and the sialons Sr₃Ln₁₀Si₁₈Al₁₂O₁₈N₃₆ (Ln=Ce, Pr, Nd) and Sr₁₀Sm₆Si₃₀Al₆O₇N₅₄ were synthesised as coarsely crystalline products by high-temperature reaction using a radiofrequency furnace. The crystal structures were determined by single-crystal X-ray diffraction and powder neutron-diffraction (Ce₄[Si₄O₄N₆]O and Sr₃Pr₁₀Si₁₈Al₁₂O₁₈N₃₆). Ce₄[Si₄O₄N₆]O represents the first hyperbolically layered silicate. The Si/O/N network is built up of Q³ type SiON₃ tetrahedra enveloping the large [Ce₄O]¹⁰⁺ cations. The sialons Sr₃Ln₁₀Si₁₈Al₁₂O₁₈N₃₆ contain a complex network of corner sharing SiON₃, SiN₄, and AlON₃ tetrahedra, while Sr₁₀Sm₆Si₃₀Al₆O₇N₅₄ is built up by a capped double-layer structure of SiON₃, SiN₄, AlON₃, and AlN₄ tetrahedra. The crystallographic ordering of Al/Si and O/N, respectively, was investigated by refinement of the neutron powder diffraction data and lattice energy calculations (MAPLE) on the basis of the single-crystal X-ray diffraction data. Hardness investigations using single crystals of Sr₃Pr₁₀Si₁₈Al₁₂O₁₈N₃₆ yielded an averaged Vickers hardness of 22.0 GPa.