Thermoelectric properties of Ca3Co4O9-based ceramics textured by templated grain growth method

We fabricated highly textured Ca₃Co₄O₉-based ceramics by using plate-like particles as a template in order to extract highly anisotropic thermoelectric properties. Plate-like powder and fine powder of (Ca_2.7Na_0.15Bi_0.15)Co₄O₉ were synthesized and wet-mixed at the ratio of 1:4. The slurry was tape-cast into a form with the platelets aligned parallel to the tape surface. The tapes were stacked, and sintered or hot-pressed at 1193 K. The resultant ceramics showed highly preferred orientation with the {001} plane parallel to the tape surface. The electrical conductivity in the direction of the ab-plane was improved to 1.8×10⁴ S/m at 1073 K by the texture given. The maximum power factor reached 5.9×10^-4 W/mK² at the same temperature.