2024/12/17 by Kruppa, Katharina, Hennig, Tobias, Escobar Cano, Giamper +2
#600 | Technik::660 | Technische Chemie #ceramic matrix composites #electrical conductivity #oxides #thermoelectric properties
paper · doi:10.15488/18263
Sodium cobaltite (NaxCoO 2 ) is one of the most renowned and thermoelectrically promising p-type cobalt oxide materials, showing exceptional performance in this domain. Nonetheless, its thermal instability in air renders it unsuitable for high-temperature applications such as energy harvesting from industrial waste heat. To utilize the beneficial properties of NaxCoO 2 , microscale NaxCoO 2 template particles of significantly larger size were effectively embedded within a thermally stable Ca3 Co 4−yO 9+δ–NaxCoO 2 –Bi2 Ca2 Co 2 O 9 triple-phase matrix. This approach additionally aimed to enhance the texture and boost the thermoelectric performance of the ceramic composite. Highly textured p-type ceramic composites were fabricated via uniaxial cold-pressing and pressureless sintering in air. The unique hexagonal NaxCoO 2 template particles, produced through molten-flux synthesis, allowed precise control over their shape and dimensions, while the matrix was synthesized via a sol–gel synthesis. The integrated NaxCoO 2 particles of the textured composite exhibited increased thermal stability, showing no sign of decomposition at 1173 K in air, whereas the sole template particles decomposed at 1073 K during sintering. A 20 wt% template particle content in the textured composites resulted in a remarkably high and nearly temperature-independent power factor of 8.8 µW cm−1 K2 , corresponding to an improvement of 13% compared to that of the pure matrix material.