An analysis of crystal structure of Ca-deficient oxonitridoaluminosilicate, Ca0.88Al0.91Si1.09N2.85O0.15

A polycrystalline, Ca0.88Al0.91Si1.09N2.85O0.15, was synthesized by a solid state reaction in the ternary system Ca3N2, AlN, and Si3N4, which was accompanied by a two-step heat treatment, 1600°C for 2 h and then 1800°C for 2 h under the nitrogen pressure of 0.92MPa. The space group of the polycrystalline was confirmed as orthorhombic Cmc21 (36) by means of a convergent-beam electron diffraction (CBED). The lattice parameters were refined using the Rietveld method to be a = 980.005(8), b = 564.928(4), and c = 506.241(3) pm with the corresponding weighted profile residual, Rwp = 0.092. Ca0.88Al0.91Si1.09N2.85O0.15 was formed due to the creation of cation vacancies at Ca2+ site in CaAlSiN3, which has the isomorphic structure with LiSi2N3 and NaSi2N3, by partial replacement of N3- by O2-.