Effect of platelet template seeds on microstructure and thermoelectric properties of Ca₃Co₄O₉ ceramics

Plate-like Ca₃Co₄O₉ microcrystal particles were synthesized by molten salt synthesis. Denser Ca₃Co₄O₉ thermoelectric ceramics were fabricated by utilizing morphologically optimized particles as the template seeds. Effects of Ca₃Co₄O₉ template seeds on microstructure and thermoelectric properties of ceramics were investigated. The results showed that weight ratios of salt to oxides (s/o) had great influence on components, microstructure, and grain size of template seeds. The particles displayed satisfactory morphology and uniform grain size when the ratio of s/o reached 1, with a mean grain size of 7.92 µm in diameter and 1.13 µm in thickness. The bulk density of Ca₃Co₄O₉ ceramics was 92.5% in the presence of 40 wt% of the template seed. The thermoelectric properties were measured from 50 °C to 800 °C. The results showed an electrical resistivity of 20.3 mΩ cm, a Seebeck coefficient of 179 μV/K and a power factor of 0.16 mW/m K². The ZT value can reach 0.15 at 800 °C, which is 1.6 times higher than that of conventional Ca₃Co₄O₉ thermoelectric ceramics.