2.
Ca
3Co
4O
9 is a promising p-type thermoelectric oxide material having intrinsically low thermal conductivity. With low cost and opportunities for automatic large scale production, thick film technologies offer considerable potential for a new generation of micro-sized thermoelectric coolers or generators. Here, based on the chemical composition optimized by traditional solid state reaction for bulk samples, we present a viable approach to modulating the electrical transport properties of screen-printed calcium cobaltite thick films through control of the microstructural evolution by optimized heat-treatment. XRD and TEM analysis confirmed the formation of high-quality calcium cobaltite grains. By creating 2.0 at% cobalt deficiency in Ca
2.7Bi
0.3Co
4O
9+δ, the pressureless sintered ceramics reached the highest power factor of 98.0 μWm
?1 K
-2 at 823 K, through enhancement of electrical conductivity by reduction of poorly conducting secondary phases. Subsequently, textured thick films of Ca
2.7Bi
0.3Co
3.92O
9+δ were efficiently tailored by controlling the sintering temperature and holding time. Optimized Ca
2.7Bi
0.3Co
3.92O
9+δ thick films sintered at 1203 K for 8 h exhibited the maximum power factor of 55.5 μWm
?1 K
-2 at 673 K through microstructure control.
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