Structure and properties of the one-dimensional cobalt oxide CaCo2O4

We have studied crystal structure and transport properties of the quasi one-dimensional cobalt oxide CaCo2O4. The CaCo2O4 phase crystallizes in calcium-ferrite type structure, which consists of a corner- and edge-shared CoO6 octahedron network including one-dimensional double chains. Large thermoelectric power (S ∼ 150 μV/K at 390 K) with metallic temperature dependence of S, moderate resistivity (ρ ∼ 2.9 × 10−1 Ω cm at 390 K) with carrier localization at low temperature, and normal thermal conductivity (κ ∼ 6.3 W/Km at 390 K) were observed. The phonon mean-free path was calculated from the observed data, as a function of temperature. The long phonon mean-free path (l ∼ 24 Å at 300 K) implies that the thermal conductivity could be suppressed by impurity scattering of phonons with partial element substitution.