The preparation, crystallography, and magnetic properties of the LixCo(1−x)O system

The LixCo(1−x)O system has been prepared by the solid-state reaction between Li2O2 and CoO at 900°C. The material is a single-phase structure in the composition range 0 < x < 0.2, the lattice parameter of the cubic unit cell decreasing with increasing lithium content. At the composition x = 0.5 (i.e. LiCoO2) a rhombohedral structure is formed. A phase diagram for this system has been developed. The crystal structure of material in the composition range 0 < x < 0.2 has been studied both above and below the antiferromagnetic Curie temperature. Both the antiferromagnetic Curie temperature and the related cubic-tetragonal transformation are found to occur at decreasing temperatures with increasing lithium content. In addition the magnitude of the crystallographic deformation decreases and finally vanishes with increasing lithium content. The magnetic-susceptibility data indicate that the magnetic moment of Co+2 is best understood if the multiplet splitting is small compared to kT. Further, the moment of Co+3 is shown to be lowered by crystalline field effects. No effects attributable to the double exchange coupling were found. The absence of such a coupling is understood by consideration of the mechanism of electron transfer in the lithium-substituted compounds.