Enhanced thermoelectric performance of Ca3Co4O9 doped with aluminum

Abstract

Ca3−x AlxCo4O9 polycrystalline ceramics with a small amount of Al (0 ≤ x ≤ 0.4) were fabricated using the sol–gel combustion method with natural starch as a fuel. All synthesized samples were a pure phase with no Al-based secondary phase detected, and a defect-free lattice structure. Their diffraction peaks shifted to higher angle values as doping (x) increased. A mixture of valence states of Co2+, Co3+, and Co4+ were detected in all samples. In the Ca3Co4O9 system, both the Seebeck coefficient and the thermal conductivity are enhanced by a single doping of Al. The maximum power factor (0.348 mW/m K2) and figure of merit (0.14) was obtained for x = 0.1 at 700 K; these values are respectively 3.6% and 28.4% higher than undoped samples. These results indicate that Al is a promising doping element for enhancing the thermoelectric properties of the Ca3Co4O9 system.