High-temperature thermoelectric properties of Sm3+-doped Ca3Co4O9+δ fabricated by spark plasma sintering

Ca3-xSmxCo4O9+δ (0 ≤ x ≤ 0.3) samples were fabricated by the sol-gel method followed by spark plasma sintering in vacuum. The high-temperature thermoelectric properties of the Ca3-xSmxCo4O9+δ were also studied, with an emphasis placed on the partial substitution of Sm3+ for Ca2+. The sintered Ca3-xSmxCo4O9+δ formed a monoclinic Ca3Co4O9 phase and exhibited fine lamellar grains and dense morphology. With increased Sm3+ content, the electrical and thermal conductivities decreased, whereas the Seebeck coefficient significantly increased. Of the prepared samples, Ca2.7Sm0.3Co4O9+δ had the largest dimensionless figure-of-merit (0.175) at 800 °C. The results showed that the partial substitution of Sm3+ for Ca2+ in Ca3Co4O9+δ is effective for enhancing its thermoelectric properties.