THE CRYSTAL-STRUCTURE OF BAIRO3

The X-ray crystal structure of BaIrO3 has been determined using a four-circle diffractometer and a small untwinned crystal grown in a molten BaCl2, flux. The single crystal studies indicated the space group C2/m with unit cell parameters: a = 10.0052(4) angstrom, b = 5.7514(2) angstrom, c = 15.1742(7) angstrom, and beta = 103.274(5)degrees. The crystal structure of BaIrO3 is similar to that of the nine-layer BaRuO3, but with a monoclinic distortion. It is also closely related to the structure recently reported for the compound Ba7Ir6O19. The structure consists of three face-shared IrO6 octahedra that are linked by terminal vertices to other trimeric clusters along the c-axis. The Ba atoms mostly remain in 12-coordinated sites, these sites are similar to those found in other hexagonal-layer perovskite polytypes. The original 18R structure, observed on multi-twinned crystals, is only an approximate pseudo-structure, and this model did not yield a suitable refinement to the actual structure since single crystals lack the three-fold axis. The stoichiometry was determined from chemical analysis, and this was further supported by the refinement of population and thermal parameters.