Single-crystal growth, crystal and electronic structure of NaCoO2

Single crystals of NaCoO2 have been successfully synthesized for the first time by a flux method at 1323 K. A single-crystal X-ray diffraction study confirmed the trigonal R(3) over bar m space group and the lattice parameters a = 2.8897(15) Angstrom, c = 15.609(3) Angstrom. The crystal structure has been refined to the conventional values R = 1.9% and wR = 2.1% for 309 independent observed reflections. The electron density distribution of NaCoO2 has been studied by the maximum entropy method (MEM) using single-crystal X-ray diffraction data obtained at 298 K. From the results of the MEM analysis, the strong covalent bonding was clearly observed between Co and O atoms, while no bonding was observed around Na atoms. We also calculated the electron density of NaCoO2 by first principles calculations. The electron density obtained experimentally is in good agreement with the theoretical one. (C) 2002 Elsevier Science (USA). All rights reserved.