X-ray diffraction study of K₃NdSi₇O₁₇: A new framework silicate with a linear Si-O-Si bond

Hydrothermal investigations in the high-silica region of the K₂O-Nd₂O₃-SiO₂ system, carried out in a search for novel fast-ion conductors (FICs), yielded the new compound tripotassium neodymium heptasilicate, K₃NdSi₇O₁₇. Single-crystal X-ray methods revealed that K₃NdSi₇O₁₇ crystallizes in space group P3, has lattice constants a = 16.131 (2) and c = 7.7146 (19) Å, Z = 4, and 22 atoms in the asymmetric unit. Refinement was carried out to a residual. R(F), of 0.0253 and a weighted residual, wR(F²), of 0.0702 using anisotropic displacement parameters for all atoms. The silicate anion forms an interrupted framework, within which both Nd octahedra and K polyhedra are situated. The structure is unusual in that it contains a symmetry-constrained Si-O-Si bond angle of 180°. No isomorphs to K₃NdSi₇O₁₇ are known.