Mott-type hopping conduction in the ordered and disordered phases of LiCoO2

The temperature dependence of dc resistance (R)[ln(R) vs T−1/4] was observed in the range of 170<T<300 K for layered-rock-salt (hexagonal structure, ordered distribution between Li and Co) and modified-spinel (cubic, random distribution) phases of LiCoO2. The results suggest Mott-type hopping conduction arising from the localized Co-3d electrons in the valence band. The densities of states (DOS) at the Fermi energy (EF) estimated from the slope of the resistance curves were 2.0×1020 and 5.5×1019 cm−3 eV−1 for the ordered and disordered phases, respectively. The relatively low DOS at EF in the disordered phase suggests that EF approaches the edge of the valence band as a result of the narrowing of Co-t2g bands due to the higher lattice symmetry in the disordered phase.