Thermoelectric properties of Ca/sub 3/Co/sub 4/O/sub 9/-based ceramics textured by templated grain growth method

We fabricated highly textured Ca/sub 3/Co/sub 4/O/sub 9/-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/sub 2.7/Na/sub 0.15/Bi/sub 0.15/)Co/sub 4/O/sub 9/ 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/spl times/10/sup 4/ S/m at 1073 K by the texture given. The maximum power factor reached 5.9/spl times/10/sup -4/ W/mK/sup 2/ at the same temperature.