Fabrication and thermoelectric properties of highly textured Ca9Co12O28 ceramic

• Highly textured Ca9Co12O28 ceramics have been prepared by hot pressing method.
• TE properties of the samples show bidimensional anisotropic character.
• Lattice thermal conductivity is the main thermal transference in the samples.
• At 600 °C the samples have a ZT = 0.18 in the direction perpendicular to the hot pressing direction.

Ca9Co12O28 thermoelectric ceramics were fabricated by both sintering and hot-pressing methods. The hot pressed ceramic has a layered structure, and exhibits {0 l 0} preferred orientation and a high orientation degree of 0.84 calculated from the XRD patterns. Thermoelectric properties of the sintered and hot pressed samples were measured from 100 °C to 600 °C. For the hot pressed sample, the electrical conductivity in the direction perpendicular to the pressing direction is much higher than that in the direction parallel to the pressing direction. Thermal conductivity of the hot pressed sample is also anisotropic, and the lattice thermal conductivity is the main thermal transference. In the direction perpendicular to the pressing direction, the hot pressed sample shows a high ZT value of 0.18 at 600 °C.

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