Thermoelectric properties of Ca3Co4O9 ceramics prepared by an alternative pressure-less sintering/annealing method

Fast preparation route to high-performances textured Sr-doped Ca3Co4O9 thermoelectric materials through precursor powder modification

“…Moreover, they are comparable to the reported in spark plasma sintered (SPS) materials (7-8 mΩ cm) [13,32,33]. When evaluating the hightemperature values determined in this work (5.7-5.9 mΩ cm) with the best reported in the literature, once again they are much lower than the determined in sintered materials or prepared via alternative methods (34-16.5, and 10-12.5 mΩ cm, respectively) [13,18,[28][29][30][31]. Furthermore, they remain similar to the measured in SPS textured samples (6-7 mΩ cm) [13,32,33].…”

“…As it can be observed in the graph, they show very similar semi- conducting-like behaviour (dρ/dT≤0), and values in the whole measured temperature range. The minimum values at room temperature (RT), 8.3 mΩ cm, are lower than the reported for sintered specimens (15-30 mΩ cm) [13,18,28], or prepared through alternative methods (11-15 mΩ cm) [29][30][31]. Moreover, they are comparable to the reported in spark plasma sintered (SPS) materials (7-8 mΩ cm) [13,32,33].…”

“…This behavior can be explained taking into account that Ca 3 Co 4 O 9 phase is known to lose oxygen at high temperatures, decreasing the carrier concentration [35], and this process is faster when the number of grain boundaries is raised. When comparing the highest S determined at room temperature and 800°C (145 and 205 μV K −1 , respectively), they are in the order of the reported for sintered, prepared through alternative methods or SPS (125-150, and 155-230 μV K −1 , at RT, and 800°C, respectively) [13,18,[28][29][30][31][32][33].…”

Improving thermoelectric properties of Ca3Co4O9+δ through both Na doping and K addition at optimal values

“…carrier concentration and mobility [3,27,28], which can be increased in this case by doping and a rise in density. The minimum resistivity value at 800 ºC (15 m cm) is lower than that measured in classically sintered materials (34-16.5 m cm) and similar to those reported for materials prepared through advanced techniques (10-12.5 m cm) [26,[29][30][31][32][33]. From these data, it is clear that the process used in this work is useful to obtain low electrical resistivity materials, when compared with those composed of randomly oriented grains, which is favourable for increasing power factor [34,35].…”

“…Moreover, K 2 CO 3 addition significantly increases PF until 3 wt.%, slightly reducing it for higher K content. The highest PF at 800ºC has been determined in 3 wt.% K 2 CO 3 samples (0.28 mW/K 2 m), which is in the order of those reported for materials sintered classically, or prepared through alternative methods (0.14-0.42 mW/K 2 m) [26,[29][30][31][32][33].…”