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Enhanced densification and thermoelectric properties of Ca3Co4O9 ceramics fabricated by solid-state combustion and hot-pressing
Author(s)
Thatawong, Bhoowadol
Sriondee, Manlika
Chongsatan, Wistsarut
Palaporn, Dulyawich
Pinitsoontorn, Supree
Rittidech, Aurawan
Rattanachata, Arunothai
Suriwong, Tawat
Bongkarn, Theerachai
Date Issued
November 15, 2026
Type
Article
Abstract
The Ca3Co4O9 powders were synthesized by the solid-state combustion method and then calcined at 775-875 °C for 6 h. The combination of combustion-derived fine powders and hot pressing was adopted to improve the densification and thermoelectric (TE) performance of Ca3Co4O9 ceramics. Dense Ca3Co4O9 ceramics were subsequently fabricated by hot-pressing to investigate the influence of hot-pressing temperature (800-950 °C, 2 h) on phase formation, microstructure, electrical, and TE properties. The Ca3Co4O9 powder was obtained after calcination at 800 °C for 6 h and exhibited an average particle size of 0.55 μm. XRD analysis confirmed that Ca3Co4O9 was the predominant phase in all hot-pressed samples. XPS analysis further confirmed the presence of oxygen vacancy (VO++)-related defects and mixed-valence cobalt species. FESEM observations revealed a dense microstructure composed of plate-like grains with an average grain size ranging from 0.61 to 0.96 μm. The bulk density ranged from 4.31 to 4.46 g/cm3, indicating dense ceramics. The electrical resistivity (ρ) decreased with increasing measured temperature for all samples. Among all samples, the ceramic hot-pressed at 900 °C exhibited the lowest ρ at 600 °C. The Seebeck coefficient (S) significantly increased from 150 μV/K to 223 μV/K, while the thermal conductivity (κ) decreased with increasing temperature. Due to the favorable combination of low ρ and high S, the sample hot-pressed at 900 °C achieved the highest power factor (PF) and a maximum dimensionless figure of merit (ZT) of 0.17 at 600 °C.
Citation
Materials Science in Semiconductor Processing, 215, 2026