Thermoelectric Properties of the One-Dimensional Cobalt Oxide CaCo2O4

In this work we studied the crystal structure and physical properties of the new one-dimensional cobalt oxide CaCo2O4+delta . The CaCo2O4+delta phase crystallizes as a calcium-ferrite-type structure, which consists of a corner- and edge-shared CoO6 octahedron network including one-dimensional double chains. The specific-heat Sommerfeld constant gamma was found to be 4.48(7) mJ/mol K-2. This result suggests that the CaCo2O4+delta phase has a finite density of states at the Fermi level. Metallic temperature dependence of the Seebeck coefficient S with a large thermoelectric power (S = 151 mu V/K at 387 K) was observed. The origin of the large thermoelectric power may be attributed to the quasi one-dimensional character of the energy band near the valence band maximum in CaCo2O4+delta .