Influence of ceramic particles additions on the properties of Ca3Co4O9

Abstract Ca 3 Co 4 O 9 + x wt% B 4 C, AlN, TiC, TiB 2 , or TiN (x = 0.0, 0.25, 0.50, and 0.75) samples were prepared by the conventional solid-state route. In all samples, only the Ca 3 Co 4 O 9 phase was identified by powder XRD. Nevertheless, microstructural studies have shown that most of the additives have reacted with air and Ca 3 Co 4 O 9 phase on their surfaces, producing new phases. Moreover, it seemed that grain sizes were, at least, slightly reduced. On the other hand, while nearly no modification of the Seebeck coefficient has been observed, independently of the added compound and proportion, electrical resistivity decreased in all cases, when compared to the pristine sample. Consequently, the power factor of samples with additions was higher than the one determined for the pure sample. Linear thermal expansion also decreased with these additives, pointing out to the formation of relatively strong grain boundaries which can improve the carrier mobility and decrease the thermal expansion. The lowest thermal expansion value has been measured in 0.25 wt% B 4 C samples, being only around 20% higher than that of Al 2 O 3 , which can help to reduce the differential thermal expansion in thermoelectric modules working at high temperatures; these results may be very interesting for applications prospects. Article highlights Addition of different ceramic additives to Ca 3 Co 4 O 9 phase increases electrical conductivity, and power factor. All additive ceramics react with oxygen and the Ca 3 Co 4 O 9 phase modifying the properties of pristine compound. The decrease of thermal expansion coefficient will allow reducing the differential thermal expansion in modules.