Microstructure and high-temperature thermoelectric properties of CuO and NiO co-substituted NaCo 2O 4

Abstract

The partial substitution of Cu for Co in Na(Co 1− z Ni z ) 2O 4 (0 ≤ z ≤0.15) led to an increase in the electrical conductivity ( σ) mainly because of an increase in the hole concentration, density, and grain size of sintered bodies. On the other hand, the partial substitution of Ni for Co in Na(Co 1− y Cu y ) 2O 4 (0 ≤ y ≤ 0.15) gave rise to a decrease in the electrical conductivity mainly because of a decrease in the density and grain size. In particular, the Cu and/or Ni substitution led to a significant increase in the Seebeck coefficient ( α). The power factor ( σα 2) was substantially improved by the partial co-substitution of Cu and Ni for Co in NaCo 2O 4. The highest value of power factor (3.27 × 10 −3 Wm −1 K −2) was attained for Na(Co 0.7Cu 0.15Ni 0.15) 2O 4 at 1073 K. It is concluded that the Cu and Ni co-substitution is effective for enhancing high-temperature thermoelectric properties.