STRUCTURE OF NA3NDSI6O15-CENTER-DOT-2H(2)O - A LAYERED SILICATE WITH PATHS FOR POSSIBLE FAST-ION CONDUCTION

Hydrothermal investigations of the high silica region of the Na2O-Nd2O 3-SiO2 system, carried out in the search for new fast-ion conductors ( FIC's), yielded the compound Na3NdSi6O15.2H(2)O (sodium neodymium sili cate). Single-crystal X-ray methods provided lattice constants of a=7. 385 (2), b=30.831 (7) and c=7.1168 (13) Angstrom, space group Cmm2, an d 22 atoms in the asymmetric unit. With four formula units per unit ce ll, the calculated density is 2.68 g cm(-3). Refinement was carried ou t with 1113 independent structure factors to a weighted residual wR(F) of 2.63% [8.09% for wR(F-2)] using anisotropic temperature factors fo r all atoms. The structure, based on corrugated Si6O15 layers containi ng four-, five-, six- and eight-membered rings, is related to that of a model previously reported for a compound assigned the composition Na NdSi6O13(OH)(2).nH(2)O. Our structure differs in the placement of sodi um ions and water molecules, and contains no hydroxyl groups, We belie ve that both studies examined the same phase.