A SERIES OF CHEMICALLY-TWINNED-RUTILE OXIDES, SRM2N-]9)(1O4N+5 (M=TI,NB, N=3)

X-ray powder diffraction data and refined unit cell parameters for SrT i3Nb4O17, SrTi5Nb4O21, SrTi7Nb4O25, SrTi9Nb4O29, SrTi11Nb4O33, SrTi13N b4O37, and SrTi15Nb4O41 are reported here. The powder patterns for the se oxides suggest that they form a homologous series SrM2n+1O4n+5 (M = Ti, Nb; n = 3 --> 9), which is isostructural with the orthorhombic '' chemically twinned rutile'' series found previously in the K2O-TiO2-Ta 2O5 and BaO-TiO2-Nb2O5 systems. The structures are built of corner-sha ring slabs of the rutile structure; successive members are generated b y adding 2TiO(2) to the slab thickness of the previous member. The ser ies crystallizes in space group Cmcm (No. 63), with members exhibiting similar a-, b-dimensions (similar to 6.6, similar to 8.9 Angstrom; re spectively), and c-dimensions that linearly increase (by similar to 4. 4 Angstrom per member) from 20.8 Angstrom for n = 3 to 47.1 Angstrom f or n = 9. (C) 1997 International Centre for Diffraction Data.