Enhancement of thermoelectric properties in Ca₃Co₄O₉ ceramics via Lu^3 + ion doping

Despite the promising overall performance of Ca₃Co₄O₉-based thermoelectric materials, their relatively low conversion efficiency remains a key limitation for device development. Exploratory first-principles calculations demonstrate that Lu³⁺ ion doping reduces the bandgap and enhances the density of states near the Fermi level in Ca₃Co₄O₉. These electronic structure modifications are expected to improve the thermoelectric performance. Based on these predictions, we prepared Ca_3-xLu_xCo₄O₉ (x = 0.1, 0.2, 0.3) ceramics via solid-state reaction under ambient atmosphere. Experimental results indicate that Lu³⁺ ion substitution effectively reduces Co⁴⁺ ion concentration, leading to enhanced Seebeck coefficient and power factor. Specifically, the Ca_2.9Lu_0.1Co₄O₉ ceramic achieves an electrical conductivity of 5840.7 S/m, a Seebeck coefficient of 195 μV/K, a power factor of 222.44 μW/(K²·m), a thermal conductivity of 1.58 W/(m·K), and a ZT value of 0.12 at 873 K. Notably, its power factor is 19.83 times greater than that of the undoped Ca₃Co₄O₉ ceramic, and its ZT is 3 times higher. These findings provide a theoretical and experimental foundation for optimizing Ca₃Co₄O₉-based ceramics and advancing their engineering applications.