An analysis of crystal structure of Ca-deficient oxonitridoaluminosilicate, Ca_0.88Al_0.91Si_1.09N_{2.85 0.15}

A polycrystalline, Ca_0.88Al_0.91Si _1.09N_2.85O_0.15, 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, R_wp = 0.092. Ca_0.88Al _0.91Si_1.09N_2.85O_0.15 was formed due to the creation of cation vacancies at Ca²⁺ site in CaAlSiN ₃ which has the isomorphic structure with LiSi₂N ₃ and NaSi₂N₃, by partial replacement of N ^3- by O^2-.