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), yiel ded the new compound tripotassium neodymium heptasilicate, K3NdSi7O17. Sing le-crystal X-ray methods revealed that K3NdSi7O17. crystallizes in space gr oup P (3) over bar, has lattice constants a = 16.131 (2) and c = 7.7146 (19 ) Angstrom, Z = 4, and 22 atoms in the asymmetric unit. Refinement was carr ied out to a residual, R(F), of 0.0253 and a weighted residual, wR(F-2), of 0.0702 using anisotropic displacement parameters for all atoms. The silica te anion forms an interrupted framework, within which both Nd octahedra and K polyhedra are situated. The structure is unusual in that it contains a s ymmetry-constrained Si-O-Si bond angle of 180 degrees. No isomorphs to K3Nd Si7O17 are known.