Spray solution combustion synthesis of undoped Ca3Co4O9: High thermoelectric performance through grain orientation and moderate texture

Undoped Ca3Co4O9 was synthesized using spray solution combustion synthesis (SSCS) and consolidated through spark plasma sintering (SPS), resulting in a microstructure with moderate texturing [maximum Lotgering factor of 0.35 for the (004) plane] and strongly elongated, densely packed grains oriented perpendicular to the pressing direction. The presence of texture mainly influences the electrical conductivity of the obtained material, which becomes comparable with values reported in the literature for doped Ca3Co4O9. These features allowed one to achieve in the undoped Ca3Co4O9 thermoelectric figure of merit zT of 0.35 at 1050 K, which determines the importance of microstructural architecture. The study highlights that although texturing contributes to increased electrical conductivity, the synergistic combination of grain elongation and boundary architecture is key to achieving significant improvements in the performance of layered materials, demonstrating the importance of optimizing microstructural characteristics to improve functionality. Cobaltite obtained by this route has advantages over the others, due to the significant reduction in ceramic production time, as well as low cost, without the need for expensive alloying elements.