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Published February 1997 | Published
Journal Article Open

Structure of Na_3NdSi_6O_(15)._2H_2O - A Layered Silicate with Paths for Possible Fast Ion Conductor

Abstract

Hydrothermal investigations of the high silica region of the Na₂0-Nd₂0₃-SiO₂ system, carried out in the search for new fast-ion conductors (FIC's), yielded the compound Na₃NdSi₆O₁₅.2H₂0 (sodium neodymium silicate). Single-crystal X-ray methods provided lattice constants of a=7.385(2), b=30.831(7) and c= 7.1168 (13)Å, space group Cmm2, and 22 atoms in the asymmetric unit. With four formula units per unit cell, the calculated density is 2.68gcm⁻³. Refinement was carried out with 1113 independent structure factors to a weighted residual wR(F) of 2.63% [8.09% for wR(F²)] using anisotropic temperature factors for all atoms. The structure, based on corrugated Si₆O₁₅ layers containing four-, five-, six- and eight-membered rings, is related to that of a model previously reported for a compound assigned the composition NaNdSi₆O₁₃(OH)₂.nH₂0. Our structure differs in the placement of sodium ions and water molecules, and contains no hydroxyl groups. We believe that both studies examined the same phase.

Additional Information

© 1997 International Union of Crystallography. (Received 7 May 1996; accepted 24 July 1996). We are indebted to Dr Karl Peters of the Max-Planck-Institut fur Festkorperforschung for providing single-crystal intensity data and to Dr Peter Hohn for aid with the structure determination. Nubia Carioca, also of MPI, kindly performed TGA experiments and Mike Jercinovic, of the Massachusetts Institute of Technology, supplied the results of microprobe analyses. Figures were drawn using the ATOMS program by Shape Software. S. Haile is grateful to the AT&T Cooperative Fellowship Program, the Fulbright Foundation and the Alexander von Humboldt Foundation for providing financial support at various stages of this research.

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August 19, 2023
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