Several studies have investigated oxide thermoelectric systems such as CaMnO3 [3,4] and SrTiO3 [5,6] ceramics. Ca3Co4O9 ceramics have also been widely studied owing to their nontoxicity, high oxidation resistance, and chemical and thermal stabilities at high temperatures. These properties make Ca3Co4O9 ceramics appropriate for applications as thermoelectric materials [7,8]. The thermoelectric properties of Ca3Co4O9 ceramics are dependent on their layered structure, which consists of a CoO₂layer with high electrical conductivity interleaved with a Ca2CoO3 thermal insulator layer [9].