Incommensurate Cu/Co Ordering in the TlCo2-xCuxSe2 (x~1) System

The crystal structure of BaRuO3 has been derived by the bond valence method and sphere packing geometry using only the information obtained from the indexing of a powder pattern of the compound. The structural parameters derived in this way give calculated bond distances that agree with those measured experimentally to within 0.02 ?. Since the Ba–O and Ru–O distances that completely satisfy the valence requirements of the atoms are incommensurate under the constraints imposed by the geometry of the structure, the Ba–O and Ru–O bonds of the final model are, on the average, compressed and stretched, respectively. As a result of this analysis it is found that the valences of the two crystallographically independent Ru atoms in the asymmetric unit are very nearly equal. The structure of BaRuO3 is formed by units of three face-sharing RuO6 octahedra, connected to one another by corner sharing. The oxygen atom of the shared faces in each unit are pulled together, thus providing a "shielding effect" that reduces the Ru–Ru interactions.