Crystal structures of Ca Y SiO N (0 ≤ ≤ 1) comprising of an isolated [Si(O,N)] unit.

Single crystals of the solid solution series Ca Y SiO N were obtained by a solid-state reaction method using a flux for = 0, 0.5 and 1, resulting in CaYSiON (tetra-calcium triyttrium hepta-silicon oxynitride), CaYSiON and CaYSiON (penta-calcium diyttrium hepta-silicon oxynitride). Single-crystal X-ray analysis revealed that the three compounds are isotypic and belong to space-group type 6/. Ca and Y cations are distributed over two crystallographic sites (site symmetry .. and 1) in a disordered manner. The corresponding (Ca,Y)-centred polyhedra are connected by edge-sharing, resulting in the formation of a layer structure extending parallel to (001). Three [Si(O,N)] tetra-hedra (two with point group symmetry .., one with 3.. and half-occupancy) are condensed into an isolated [Si(O,N)] unit, in which an [Si(O,N)] tetra-hedron is located at the center of a 12-membered oxynitride ring with composition [SiON]. The present compounds are the first to have such an [Si(O,N)] unit in their structures.