The effects of Ga substitution on the Co-site on the high-temperature thermoelectric properties and microstructure are investigated for the misfitlayered Ca 3Co 4O 9 and the complex perovskite-related Sr 3RECo 4O 10.5 (RE = rare earth) cobalt-based oxides. For both systems, substitution of Ga for Co results in a simultaneous increase in the Seebeck coefficient (S) and the electrical conductivity (σ), and the influence is more significant in the high temperature region. The power factor (S 2 σ) is thereby remarkably improved by Ga substitution, particularly at high temperatures. Texture factor calculations using x-ray diffraction pattern data for pressed and powder samples reveal that the Ga-doped samples are highly textured. Microstructure observed by scanning electron microscopy shows very well-crystallized grains for the samples with Ga substitution for Co. Among the Ga-doped samples, Ca 3Co 3.95Ga 0.05O 9 shows the best ZT value of 0.45 at 1200 K, which is about 87.5% higher than the nondoped one, a considerable improvement.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Electrical and Electronic Engineering
- Materials Chemistry