STRUCTURAL DETERMINATION OF A NEW LAMELLAR TELLUROSILICATE, ALSITE3

The tellurosilicate family has been enlarged by the syntheses of alumi nium and scandium derivatives, AlSiTe3 and ScSiTe3. They appear to be built from the same tellurium hexagonal compact stacking, metal atoms and silicon pairs distributed in octahedra of every other sheet, in th e 2/1 ratio. X-ray diffraction powder patterns are indexed in hexagona l cells with a = 6.834 4(6) angstrom and c = 6.995(1) angstrom for AlS iTe3 and a = 7.006 5(5) angstrom and c=21.292(l) angstrom for ScSiTe3. If the ScSiTe3 cell volume is consistent with that of InSiTe3 as far as ionic radii are concerned, AlSiTe3 exhibits an unexpected one. A co mplete structural determination of AlSiTe3 has been performed on a sin gle crystal. Unusual Si-Te and Al-Te distances have been found and att ributed to the pretransitional nature of aluminium.