Preparation of Ca 3 Co 4 O 9 and Improvement of its Thermoelectric Properties by Spark Plasma Sintering

The precursor powders of Ca 3 Co 4 O 9 were synthesized by a sol–gel method. The results of X‐ray diffraction and thermogravimetric and differential thermal analyses patterns indicate that pure Ca 3 Co 4 O 9 powders could be obtained by calcining the precursor at 800°C for 2 h. High dense Ca 3 Co 4 O 9 ceramic samples (∼99% of theoretical density) were prepared by the spark plasma sintering (SPS) method. Compared with the conventional sintering (CS), the SPS samples exhibit much higher electrical conductivity and power factor which are respectively about 118 S/cm and 3.51 × 10 −4 W·(m·K 2 ) −1 . The SPS method is greatly effective for improving the thermoelectric properties of Ca 3 Co 4 O 9 oxide ceramics.