Crystal structures of Ca4+ x Y3- x Si7O15+ x N5- x (0 ≤ x ≤ 1) comprising of an isolated [Si7(O,N)19] unit

Makoto Kobayashi; Takuya Yasunaga; Hideki Kato; Kotaro Fujii; Masatomo Yashima; Masato Kakihana

doi:10.1107/S2056989019001257

Crystal structures of Ca_{4+ x} Y_{3- x} Si₇O_{15+ x} N_{5- x} (0 ≤ x ≤ 1) comprising of an isolated [Si₇(O,N)₁₉] unit

Acta Crystallogr E Crystallogr Commun. 2019 Jan 25;75(Pt 2):260-263. doi: 10.1107/S2056989019001257. eCollection 2019 Feb 1.

Authors

Makoto Kobayashi¹, Takuya Yasunaga¹, Hideki Kato¹, Kotaro Fujii², Masatomo Yashima², Masato Kakihana¹

Affiliations

¹ Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
² Department of Chemistry, School of Science, Tokyo Institute of Technology, 2-12-1-W4-17, Ookayama, Meguro-ku, To-kyo 152-8551, Japan.

Abstract

Single crystals of the solid solution series Ca_4+x Y_3-x Si₇O_15+x N_5-x were obtained by a solid-state reaction method using a flux for x = 0, 0.5 and 1, resulting in Ca₄Y₃Si₇O₁₅N₅ (tetra-calcium triyttrium hepta-silicon oxynitride), Ca_4.5Y_2.5Si₇O_15.5N_4.5 and Ca₅Y₂Si₇O₁₆N₄ (penta-calcium diyttrium hepta-silicon oxynitride). Single-crystal X-ray analysis revealed that the three compounds are isotypic and belong to space-group type P6₃/m. Ca²⁺ and Y³⁺ 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)]₄ tetra-hedra (two with point group symmetry m.., one with 3.. and half-occupancy) are condensed into an isolated [Si₇(O,N)₁₉] unit, in which an [Si(O,N)]₄ tetra-hedron is located at the center of a 12-membered oxynitride ring with composition [Si₆O₁₅N₃]. The present compounds are the first to have such an [Si₇(O,N)₁₉] unit in their structures.

Keywords: crystal structure; oxynitride; silicate.

Grants and funding

This work was funded by Ministry of Education, Culture, Sports, Science and Technology grants JP16H06438, JP16H06439, and JP16H06440. Nippon Sheet Glass Foundation for Materials Science and Engineering grant . Dynamic Alliance for Open Innovation Bridging Human, Environment and Materials grant .