A NOVEL SEMICONDUCTING PEROVSKITE-RELATED PHASE - SR5NB5O17

The structure of strontium niobium oxide, Sr5Nb5O17, prepared by the floating-zone melting technique, has been determined by single-crystal X-ray analysis. The structure contains distorted perovskite-type slabs parallel to (100) formed from five NbO6 octahedra and Sr atoms. The Nb-O distances range from 1.89(2) to 2.10(2) Angstrom for Nb1, from 1.809 (5) to 2.282 (6) Angstrom for Nb2, and from 1.851 (6) to 2.167 (6) Angstrom for Nb3. The NbO6 conformations are (4+1+1) distorted. Sr2 and Sr3 are coordinated by 12 O atoms with Sr-O distances in the range 2.64 (1) to 3.04 (1) Angstrom for Sr2 and 2.50 (1) to 3.06 (1) Angstrom for Sr3. Sr1, placed near the boundary of the slab, is irregularly coordinated by five O atoms in the same slab and two O atoms in the neighbouring slab [Sr-O 2.46 (1) to 2.915 (6) Angstrom] and by a further three O atoms at long coordination distances [3.345 (8) to 3.544 (9) Angstrom]. The title compound is isotypic with La5Ti5O17 and both structures belong to the homologous series A(n+1)B(n+1)O(3n+5) with n = 4, being diamagnetic (B = Nb) or paramagnetic (B = Ti) electrically conducting compounds.