STRUCTURE OF NA3YSI6O15 - A UNIQUE SILICATE BASED ON DISCRETE SI6O15 UNITS, AND A POSSIBLE FAST-ION CONDUCTOR

Hydrothermal investigations in the high silica region of the Na2O-Y2O3 -Si6O15 system, carried out in a search for novel fast-ion conductors (FIC's), yielded the new compound trisodium yttrium hexasilicate, Na3Y Si6O15. Single-crystal X-ray methods revealed that Na3YSi6O15 crystall izes in space group Ibmm, has lattice constants a= 10.468(2), b = 15.2 467(13) and c = 8.3855(6) Angstrom, Z = 4, and 11 atoms in the asymmet ric unit. Refinement was carried out to a weighted residual of 3.53% u sing anisotropic temperature factors for all atoms. The structure is u nique in that the silica tetrahedra form isolated Si6O156- double drei er-rings, rather than layers as might be expected from the Si to O rat io of 0.4. No isomorphs to Na3YSi6015 have been reported.