An Unexpected New Member of the Family of Lithium Oxonitridosilicates - Li₇Si₂NO₆

With Li7Si2NO6, a new member of the family of lithium oxonitridosilicates with a so far unseen structure type could be synthesized. Using a high-temperature solid-state reaction in open nickel crucibles under nitrogen flow, it was possible to obtain single crystals from the starting materials SiO2, Li3N, and Li2O at temperatures of 900 & DEG;C. Single crystal X-ray diffraction data yielded lattice parameters of a=5.0934(2), b=7.4128(2), c=8.5918(2) & ANGS;, & alpha;=75.16(1)& DEG;, & beta;=87.36(1)& DEG;, & gamma;=73.01(1)& DEG; and a cell volume of V=299.75(2) & ANGS;(3). The compound, crystallizing in the triclinic space group P 1? ${\bar{1}}$ (no. 2), consists of a highly condensed anionic network built up by [SiNO3]-, [LiO4]-, and [LiN2O2]-tetrahedra as well as lithium in octahedral coordination as completing cation. With an activation barrier of 695 meV for lithium migration, Li7Si2NO6 is a potential lithium-ion conductor. The structure allows a classification not only as a sorosilicate but also as a tecto-lithosilicate and most precisely as a lithium oxonitridolithosilicate, when the different coordinations of the lithium ions are taken into account. Interestingly, the new compound is none of the several proposed representatives of the lithium oxonitridosilicates, thus expanding this substance class unexpectedly.