Thermoelectric properties and texture evaluation of Ca₃Co₄O₉ prepared by a cost-effective multisheet cofiring technique

Highly textured Ca₃Co₄O₉ thermoelectrics were fabricated by a so-called multisheet cofiring (MSC) technique in combination with the commonly practiced spark plasma sintering (SPS) technique. X-ray diffraction analysis revealed that the MSC technique significantly enhances the degree of texture compared with the conventional SPS technique. This was confirmed by microstructure analysis performed on polished and chemically etched specimens. The power factor and the thermoelectric figure of merit for the specimen produced by the MSC technique were estimated to be ~5.2 × 10⁻⁴ W/mK² and ~0.4, respectively, both of which are ~20% larger than those of the normally processed specimens. A comparative study of the thermoelectric properties, such as electrical resistivity and Seebeck coefficient, clearly demonstrated that texture mainly influences the electrical resistivity and consequently enhances the thermoelectric properties.