Doping induced spin state transition in LixCoO2 as studied by the GGA + DMFT calculations

Abstract

The magnetic properties of Li_xCoO₂ for x = 0.94, 0.75, 0.66, and 0.51 are investigated within the method combining the generalized gradient approximation with dynamical mean field theory (GGA + DMFT). A delicate interplay between Hund’s exchange energy and t_2g−e_g crystal field splitting is found to be responsible for the high-spin to low-spin state transition for Co⁴⁺ ions. The GGA + DMFT calculations show that the Co⁴⁺ ions at a small doping level adopt the high-spin state, while delithiation leads to an increase in the crystal field splitting and low-spin state becomes preferable. The Co³⁺ ions are found to stay in the low-spin configuration for any x values.