Effect of Ag substitution for Co on thermoelectric properties of NaCo/sub 2/O/sub 4/

Abstract

We have investigated the effect of Ag substitution for Co on thermoelectric properties of NaCo/sub 2/O/sub 4/. NaCo/sub 2-x/Ag/sub x/O/sub 4/ compounds with x=0-0.4 were prepared by a solid-state reaction using NaCO/sub 3/, Co/sub 3/O/sub 4/, and Ag/sub 2/O 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 NaCo/sub 2-x/Ag/sub x/O/sub 4/ were obtained for x=0-0.4. 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 NaCo/sub 2/O/sub 4/ is discussed from the transport properties, together with the results of x-ray photoelectron spectroscopy measurements.