Magnetism and structure of LixCoO2 and comparison to NaxCoO2

TL;DR

This study investigates the magnetic properties and structural changes of LixCoO2 across different lithium concentrations, revealing how Co oxidation states and lattice distortions influence magnetic behavior and comparing these features to NaxCoO2.

Contribution

It provides detailed insights into the magnetic states, structural variations, and differences between LixCoO2 and NaxCoO2, highlighting the impact of alkali content on physical properties.

Findings

Co4+ is high-spin at x=0.94-1.0 and low-spin at x=0.50-0.78

Weak antiferromagnetic coupling increases with Co4+ content

Structural differences influence physical properties in the two systems

Abstract

The magnetic properties and structure of LixCoO2 for x between 0.5 and 1.0 are reported. Co4+ is found to be high-spin in LixCoO2 for x between 0.94 and 1.0 and low-spin for x between 0.50 and 0.78. Weak antiferromagnetic coupling is observed, increasing in strength as more Co4+ is introduced. At an x value of about 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. A comparison of the structures of the NaxCoO2 and LixCoO2 systems reveals that the CoO2 layer changes substantially with alkali content in the former but is relatively rigid in the latter. Further, the CoO6 octahedra in LixCoO2 are less distorted than those in NaxCoO2. We postulate that these structural differences strongly influence the physical properties in the two systems.