Optimizing electrical and thermal transport properties of Ca3Co4O9 based thermoelectric materials by Ag and Fe co-addition

Ca3_xAgxCo4_yFeyO9 (x = 0, 0.05; y = 0, 0.1, 0.2, 0.4) polycrystalline materials were prepared by sol-gel method with spark plasma sintering. The phase composition, microstructure and high temperature thermoelectric property of the bulk samples were systematically studied. The sintered Ca3_xAgxCo4_yFeyO9 ceramics exhibit fine lamellar grain and dense morphology. Compared with single addition of Ag or Fe, appropriate co-additive amount of Ag and Fe can further increase electrical conductivity due to higher carrier concentration and mobility, while decreasing thermal conductivity by stronger phonon scattering. The coordinated regulation of electron and phonon transport is realized in Ca2.95Ag0.05Co3.8Fe0.2O9 with the maximum ZT value of 0.25 at 1000 K, which is 34 % larger than that of pure Ca3Co4O9.