Enhanced thermoelectric performance of spark plasma sintered p-type Ca3−Y Co4O9+ systems

Abstract Highly textured dense Ca3−xYxCo4O9+δ (0 ≤ x ≤ 0.3) samples were fabricated by combining sol−gel process with spark plasma sintering (SPS). Y3+ substitution for Ca2+ simultaneously increased the Seebeck coefficient and reduced the thermal conductivity. The latter was attributed to the increase in lattice anharmonicity, structural distortion, and grain boundary area, which enhanced the phonon scattering. Ca2.7Y0.3Co4O9+δ showed the largest dimensionless figure-of-merit (ZT = 0.194) at 1073 K because it had the largest Seebeck coefficient and the lowest thermal conductivity. This ZT value was 55 % larger than that of undoped Ca3Co4O9 (0.125 at 1073 K). Therefore, Y3+ substitution, sol−gel powder synthesis, and SPS are highly effective for enhancing the thermoelectric properties of Ca3Co4O9.