Single-crystal synthesis and structure refinement of the LiCoO2–LiAlO2 solid-solution compounds: LiAl0.32Co0.68O2 and LiAl0.71Co0.29O2

Abstract

Single crystals of the LiCoO2–LiAlO2 solid solution compounds LiAl0.32Co0.68O2 and LiAl0.71Co0.29O2 were synthesized by a flux method using alumina crucibles. A single-crystal X-ray diffraction study confirmed the trigonal R3¯m space group and the lattice parameters a=2.8056(11)Å, c=14.1079(15)Å, and c/a=5.028 for LiAl0.32Co0.68O2, and a=2.8023(7)Å, c=14.184(4)Å, and c/a=5.061 for LiAl0.71Co0.29O2. The crystal structures have been refined to the conventional values R=3.2% and wR=2.4% for LiAl0.32Co0.68O2, and R=3.6% and wR=3.5% for LiAl0.71Co0.29O2. The evidence of the location of Al atoms in the pseudotetragonal coordination (6c site), reported previously in LiAl0.2Co0.8O2, could not be observed in the present electron density distribution maps in both LiAl0.32Co0.68O2 and LiAl0.71Co0.29O2. The octahedral distortion analysis indicated that the Al-substitution strongly affected the distortion of the LiO6 octahedron in this solid-solution compound system, but hardly affected that of the (Al.Co)O6 octahedron.