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Start date: 2020Subject: search.filters.subject.Seebeck coefficient

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    Item type:Publication,
    Enhanced densification and thermoelectric properties of Ca3Co4O9 ceramics fabricated by solid-state combustion and hot-pressing
    (2026-11-15)
    Thatawong, Bhoowadol
    ;
    Sriondee, Manlika
    ;
    Chongsatan, Wistsarut
    ;
    Palaporn, Dulyawich
    ;
    Pinitsoontorn, Supree
    The Ca<inf>3</inf>Co<inf>4</inf>O<inf>9</inf> 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 Ca<inf>3</inf>Co<inf>4</inf>O<inf>9</inf> ceramics. Dense Ca<inf>3</inf>Co<inf>4</inf>O<inf>9</inf> 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 Ca<inf>3</inf>Co<inf>4</inf>O<inf>9</inf> 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 Ca<inf>3</inf>Co<inf>4</inf>O<inf>9</inf> was the predominant phase in all hot-pressed samples. XPS analysis further confirmed the presence of oxygen vacancy (V<inf>O</inf><sup>++</sup>)-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/cm<sup>3</sup>, 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.