Sr(3)(Al(3+x)Si(13-x))(N(21-x)O(2+x)):Eu (x ∼ 0): a monoclinic modification of Sr-sialon.

The structure of the title compound, Sr-bearing oxonitrido-aluminosilicate (Sr-sialon), contains two types of channels running along the a axis, with the three unique Sr atoms (coordinatioon number seven) residing in the larger one. The channels cross a three-dimensional Si-Al-O-N network, in which the Si and Al atoms are in a tetra-hedral coordination with N and O atoms. The chemical composition of the crystal is close to Sr(3)Al(3)Si(13)N(21)O(2) (tris-trontium trialuminium trideca-silicon henicosa-nitride dioxide), which can be expressed as a mixture of SrSiN(2), Si(3)N(4), AlN, and SiO(2) components in the molar ratio 3:3:3:1. The crystal studied was metrically orthorhombic, consisting of four twin components related by metric merohedry.