Thermopower of 2D-alkali cobaltites AxCoO2 with A = Li, Na and K

This paper is devoted to a comparative study of the A_xCoO₂ (A = Li, Na and K) systems. For x ~ 0.6, all the investigated alkali cobaltites exhibit a metallic-like behavior. Potassium cobaltites exhibit a T² dependence of the resistivity - suggesting a Fermi liquid character - and an enhanced Pauli type paramagnetism ascribed to electronic correlations. On the other hand lithium and sodium compounds show linear temperature dependence for the resistivity down to 4 K, a large thermopower above room temperature and a Curie-Weiss paramagnetism denoting larger electronic correlations. Physical properties of these cobaltites are discussed in details especially in the case of K-ordered and disordered K_0.6CoO₂ phases.