Preparation and characterization of the new oxides Ca2−xNaxCo2O5

New compounds with layered structure Ca2−xNaxCo2O5 (x=0.00–0.45) were prepared by citrate sol–gel method. X-ray powder diffraction patterns of the specimens could be indexed by two monoclinic lattices with C2 space group. The Co 2p X-ray photoelectron spectroscopy (XPS) was used to study Co chemical valence. The electrical conductivity and the thermoelectric power for the specimens were measured between 350 and 950 K. Both properties increased with rising temperature in the temperature range measured. The substitution of univalent Na+ for divalent Ca2+ had a remarkable effect on the enhancement of both properties. For Ca1.55Na0.45Co2O5 specimen, the electrical conductivity and the thermoelectric power reached 68.9 S cm−1 and 165 μV K−1 at 950 K, respectively. Their intriguing thermoelectric properties make them candidates for thermoelectric materials.