Structure of Na_3YSi_6O_(15) - a Unique Silicate Based on Discrete Si_6O_(15) Units, and a Possible Fast-Ion Conductor

摘要

Hydrothermal investigations in the high silica region of the Na₂O-Y₂0₃-Si₆O₁₅ system, carried out in a search for novel fast-ion conductors (FIC's), yielded the new compound trisodium yttrium hexasilicate, Na₃YSi₆O₁₅. Single-crystal X-ray methods revealed that Na₃YSi₆O₁₅ crystallizes in space group Ibmm, has lattice constants a=10.468 (2), b=15.2467 (13) and c=8.3855 (6) Å, Z=4, and 11 atoms in the asymmetric unit. Refinement was carried out to a weighted residual of 3.53% using anisotropic temperature factors for all atoms. The structure is unique in that the silica tetrahedra form isolated SiSi₆O₁₅⁶⁻ double dreier-rings, rather than layers as might be expected from the Si to O ratio of 0.4. No isomorphs to Na₃YSi₆O₁₅ have been reported.