Effect of NaF doping on the thermoelectric properties of Ca3Co4O9

Enhancing the Thermoelectric Performance of Calcium Cobaltite Ceramics by Tuning Composition and Processing

“…As the original SPS samples contain high volume fractions of secondary phases, and n and μ cannot be easily described by eqs and , we will focus on the annealed SPS samples; the results are presented in Table . There is minimal variation of n with composition (5.43–5.95 × 10 20 cm –3 ); this is consistent with the analysis above for σ and in broad agreement with experimental data for calcium cobaltites. , There is a positive correlation between μ and bismuth content (Table ), confirming that μ can be enhanced by increasing Bi 2 O 3 addition. It is noted that m * is almost invariant for the annealed samples (about 2.85 m 0 ), suggesting that bismuth substitution at Ca sites does not significantly modify the band structure …”

“…The electrical transport properties of the original SPS and annealed SPS Ca 3– x Bi x Co y O 9+δ ceramics are displayed in Figure . The electrical conductivity (σ//ab) for both original (13–47 S/cm) and annealed samples (70–125 S/cm) increases with temperature, indicating semiconducting behavior; the data for annealed samples show a 20% increase compared to previously reported work (20–100 S/cm). − Meanwhile, the positive Seebeck coefficients (S) (original, 137–185 μV/K and annealed, 130–165 μV/K) also increase with temperature and are consistent with earlier investigations ,, and confirm a conduction mechanism governed by holes as carriers.…”

High-temperature thermoelectric properties of Na- and W-Doped Ca3Co4O9 system

“…zT values of other doped samples are also reasonably good as listed in Table 2 . As a comparison, zT value of our x = 0.025 sample is comparable or slightly better than previously reported results of Na doped Ca 2.5 Na 0.5 Co 4 O 9 ( zT 1000 K = 0.18), 25 Bi and Na dual doped C-349 system ( zT 1073 K = 0.18), 62 Ca 2.8 La 0.2 Co 3.8 Cu 0.2 O 9 ( zT 773 K = 0.203), 40 Bi and Na substituted Ca 3 Co 4 O 9 system ( zT 1000 K = 0.32), 26 Gd and Y dual doped Ca 2.7 Gd 0.15 Y 0.15 Co 4 O 9+ δ ( zT 973 K = 0.26), 63 NaF doped Ca 3− x Na x Co 4 O 9− x F x ( zT 873 K = 0.13) 64 and Ca 2.9 Y 0.1 Co 3.97 Fe 0.03 O 9 ( zT 1000 K = 0.22) compound. 42 It has been observed that electrical resistivity of our samples is still higher than most of the previously reported results, and therefore zT values of these materials are moderate.…”

Thermoelectric Oxide Ceramics Outperforming Single Crystals Enabled by Dopant Segregations

“…Timeline of the improvement in the ZT of Ca 3 Co 4 O 9+δ polycrystalline materials by the addition of different doping elements. ,,,,− *The ZT value of this work is also reported. The goal of reaching a ZT material over 1 for commercial applications would be achievable within a few years.…”

“…The goal of reaching a ZT material over 1 for commercial applications would be achievable within a few years. Table S3 − shows historical progression of the thermoelectric properties of Ca 3 Co 4 O 9+δ .…”