Thermoelectric properties of highly textured NaCo2O4 ceramics processed by the reactive templated grain growth (RTGG) method

Highly-textured NaCo2O4 ceramics were prepared and the thermoelectric properties were examined in the preferred {001} plane. Plate-like Co3O4 particles were synthesized and used as a reactive template for c-axis oriented NaCo2O4 ceramics. Tape casting of the template particles with Na2CO3 and the following in-situ reaction produced grain-oriented ceramics topotaxially as designed. The textured ceramic specimen had in-plane electrical conductivity: 600–300 S cm−1, Seebeck coefficient, 60–120 μV K−1 and thus power factor: 2–5×10−4 W mK−2 in the temperature range from room temperature to 700°C. A large excess amount of Na and inhomogeneity in its distribution could be attributed to the lower transport properties than expected from those of a single crystal.