Microstructure and high-temperature thermoelectric properties of Cu-doped NaCo/sub 2/O/sub 4/

Cu-substituted Na(Co1-yCuy)2O4 (0≤y≤0.2) samples have been prepared using a solid-state reaction method and their thermoelectric properties studied. The electrical conductivity of Na(Co1-yCuy)2O4 decreased with increasing temperature, indicating metallic behavior. The electrical conductivity of the Cu-substituted Na(Co1-yCuy)2O4 was much higher than that of the Cu-free NaCo2O4. This is because (1) the substitution of divalent Cu 2+ for trivalent Co 3+ could increase the hole concentration of the system and (2) the Cu substitution decreased the porosity and significantly increased the grain size. In addition, the Seebeck coefficient of Na(Co1-yCuy)2O4 increased with increasing temperature and the Cu substitution led to an increase in the Seebeck coefficient. We demonstrate that extremely high power factor (3.08×10 -3 Wm -1 K -2 ) was