Compositing thermal conductivity behavior to enhance thermoelectric properties of honeycomb-like porous Ca₃Co₄O₉ ceramics

Microstructures and thermoelectric properties of porous Ca₃Co₄O₉ ceramics were investigated, which were prepared by tert-butanol alcohol (TBA)-based freeze casting method. The honeycomb-like porous Ca₃Co₄O₉ ceramic presented an average pore diameter of 2.5 μm and the porosity of 65 %. The excellent low total thermal conductivity of 0.354 W (m K)⁻¹ was obtained along the parallel channel direction, which was attributed to the oriented pores and isolated pores dispersed in ceramics matrix. The compositing thermal conductivity behavior of porous Ca₃Co₄O₉ ceramics was jointly regulated by the parallel and Maxwell-Eucken (ME-1) models. The ZT value reached 0.37 at 1073 K. This work provides an effective strategy to improve thermoelectric properties of oxides thermoelectric ceramics, which can complete the decoupling of electrical and thermal properties.