Sr4Ru3.05O12: A new member of the hexagonal perovskite family

Sr4Ru3.05O12 crystals have been synthesized under hydrothermal conditions ( 500 degrees C, 1800 bars). The crystal structure was determined by X-ray si ngle-crystal diffraction, The unit cell is hexagonal and presents a superst ructure (a(s) = root 3a(b) = 9.641(2) Angstrom and c(s) = c(b) = 18.186(5) Angstrom. The average structure has been determined (P6(3)mc space group, a (b) = 5.566(4) Angstrom c(b) = 18.186(5) Angstrom, and Z = 2). The structur e refinement converged to R = 0.057 and R-w = 0.032 for 186 independent ref lections. The crystal structure is based on the 8H (cchc)(2) close-packed s tacking of SrO3 layers with face-sharing octahedra partially occupied by th e ruthenium atoms. Electron diffraction observations and high-resolution el ectron microscopy image observations recognize the X-ray average structure. The superstructure spots appear clearly in the ED patterns and most of the crystals display diffuse streaks along c*, which are consistent with the d isorder clearly imaged in the HREM images, Heating Sr4Ru3.05O12 crystals le ads to the disappearance of the superstructure, (C) 1999 Academic Press.