Effects of Ag Addition on Microstructure and Thermoelectric Properties of Na_xCo₂O₄ Synthesized by Citric Acid Complex Process

Abstract

A thermoelectric Na_xCo₂O₄/Ag composite was synthesized by citric acid complex process using CH₃COOAg as an Ag source. The powder precursor after calcination was composed of plate-like Na_xCo₂O₄ grains and Ag particles. The Ag addition deteriorated crystallographic anisotropy of the sintered body. However, the electrical resistivity and the Seebeck coefficient of this composite were significantly smaller and slightly larger, respectively, than those of the sample without Ag, resulting in lager power factor. The Ag phase dispersed in the Na_xCo₂O₄ matrix contained about 5–17 at.% Co, which is considered to cause the increase in Seebeck coefficient.