Thermoelectric Transport Properties of Ca₃Co₄−xNixO₉+δ Oxide Materials

Nano-sized Ca3Co4−xNixO9+δ (0 ≤ x ≤ 0.3) thermoelectric powders are synthesized by using the solution combustion method, with aspartic acid as a combustion fuel. The synthesized Ca3Co4−xNixO9+δ nano-sized powders exhibit a spherical-like shape and a smooth surface. Higher Ni content results in a smaller grain size and a higher porosity, resulting in a decrease in the electrical conductivity. However, the Seebeck coefficient of Ni-added Ca3Co4O9 is much higher than that of Ca3Co4O9. The highest power factor (1.4 × 10−4 Wm−1K−2), which is more than nine times larger than that of Ca3Co4O9, is attained for Ca3Co0.38Ni0.2O9+δ at 800 ◦C. The addition of a small amount of Ni is highly effective in improving the thermoelectric properties of Ca3Co4O9. We believe that Ca3Co4−xNixO9+δ is a potential p-type thermoelectric material for renewable energy conversion.