Tailoring Ca3Co4O9 microstructure and performances using a transient liquid phase sintering additive

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, PF is increased with temperature in both cases, being slightly higher for AT samples at high temperatures. The maximum values at 800°C (0.7 mW K −2 m −1 ) are much higher than the best reported in textured materials prepared by SPS (0.45 mW K −2 m −1 ) [32] or by alternative methods (0.44 mW K −2 m −1 ) [30]. Consequently, they are among the highest obtained so far in bulk Ca 3 Co 4 O 9 polycrystalline materials reported so far in the best of our knowledge.…”

“…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].…”

Improvement of thermoelectric properties of Ca0.9Gd0.1MnO3 by powder engineering through K2CO3 additions

“…Taking into account the typical calcining temperature in this family (900°C) [8, 10], K 2 CO 3 is a good candidate as it melts below 900°C [11]. Moreover, previous studies in cobaltites thermoelectric have shown that K 2 CO 3 vanishes at 900°C even during sintering of compact pellets, having no detrimental effect on the thermoelectric performances [12]. Herein, a very facile and scalable sintering method for producing highly-performing thermoelectric ceramics with controlled porosity has been developed [12] through the addition of different amounts of K 2 CO 3 to the initial powders mixture.…”