Effect of Ag Substitution for CO on Thermoelectric Properties of NaCozOs

We have investigated the effect of Ag substitution for CO on thermoelectric properties of NaCo204. N~CO~_~A&O~ compounds with x=M.4 were prepared by a solid-state reaction using NaC03, Co304, and Ag20 as starting materials. Measurements of the Seebeck coefficient, the electrical conductivity, and the thermal conductivity were made in the wide temperature range. Polycrystalline samples of p-type N~CO~-~A&O~ were obtained for x=(M.4. The electrical conductivity increased with increasing composition x, and the Seebeck coefficient was almost independent of x in the range of x=0-0.2. The effect of Ag substitution for CO on the electronic structure and thermoelectric properties of NaCo204 is discussed from the transport properties, together with the results of x-ray photoelectron spectroscopy measurements.