The magnetic properties and structure of ${\mathrm{Li}}_x\mathrm{Co}{\mathrm{O}}_2$ for $0.5<x<1.0$ are reported. ${\mathrm{Co}}^{4+}$ is found to be high spin in ${\mathrm{Li}}_x\mathrm{Co}{\mathrm{O}}_2$ for $0.94⩽x⩽1.00$ and low spin for $0.50⩽x⩽0.78$. Weak antiferromagnetic coupling is observed, and at $x\approx 0.65$ the temperature-independent contribution to the magnetic susceptibility and the electronic contribution to the specific heat are largest. Neutron diffraction analysis reveals that the lithium oxide layer expands perpendicular to the basal plane and the Li ions displace from their ideal octahedral sites with decreasing $x$. Comparison of the structures of ${\mathrm{Na}}_x\mathrm{Co}{\mathrm{O}}_2$ and ${\mathrm{Li}}_x\mathrm{Co}{\mathrm{O}}_2$ reveals that the $\mathrm{Co}{\mathrm{O}}_2$ layer changes substantially with alkali content in the former but is relatively rigid in the latter, and that the $\mathrm{Co}{\mathrm{O}}_6$ octahedra in ${\mathrm{Li}}_x\mathrm{Co}{\mathrm{O}}_2$ are less distorted.

• Received 19 October 2007

DOI:https://doi.org/10.1103/PhysRevB.77.075119