Abstract
•The effects of cobalt deficiency on thermoelectric performance of solid state synthesized Ca2.7Bi0.3CoyO9+δ (y = 3.92, 3.96 and 4.0) bulk ceramics were investigated.•The thermoelectric response of the textured screen-printed Ca2.7Bi0.3Co3.92O9+δ thick films were efficiently tailored by controlling sintering conditions.•The mechanism of the order-disorder transition in the structural grain arrangements near the interface was analyzed.
Ca3Co4O9 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 Ca2.7Bi0.3Co4O9+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 Ca2.7Bi0.3Co3.92O9+δ were efficiently tailored by controlling the sintering temperature and holding time. Optimized Ca2.7Bi0.3Co3.92O9+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.