Enhanced Thermoelectric Performance Induced by Misplaced Substitution in Layered Ca₃Co₄O₉

Abstract

Thermoelectric properties of the Ca 3 Co 4 O 9 system have been enhanced through an exotic route: Na doping at Co site, namely misplaced substitution. To compare, we have also performed the research of Na doping at Ca site and Co vacancy. In view of the analysis of XRD, XPS, and Raman data, Na + ions could be suggested to enter into Co sites of [CoO 2 ] layers in Ca 3 Co 4−x Na x O 9 (x = 0, 0.05, 0.10) and Ca sites of [Ca 2 CoO 3 ] layers in Ca 2.90 Na 0.10 Co 4 O 9 , respectively. And Co ions are omitted from [CoO 2 ] layers in Ca 3 Co 3.90 O 9 . Among all samples, Ca 3 Co 3.90 Na 0.10 O 9 shows the maximum ZT value, which at room temperature reaches to ∼0.0117. Such a value is about 150% larger than that of Ca 3 Co 4 O 9 and 63% larger than that of Ca 2.90 Na 0.10 Co 4 O 9 . The results indicate that the misplaced substitution is more beneficial to enhance the thermoelectric performance of Ca 3 Co 4 O 9 system, compared with the traditional idea with Na doping at Ca site. Such an enhancement is mainly attributed to the combined action of electronic correlation, locally modified band structure near Fermi level, and carrier concentration.

Tuning of conductive type and magnetic properties of Ca3Co2O6 ceramics through Pb‐doping

“…So, the decrease in ρ for the samples with x ≤0.15 originates from the increased n ‐type carrier concentration induced by Pb 4+ doping, whereas the appearance of Ca 3 Co 4 O 9 impurity phase is the main source of the decrease in ρ for the heavily doped samples with x ≥0.2. To clarify the transport mechanism for these Pb‐doped samples, the ρ( T ) data are fitted using the thermal activated (TAC) law: ρ=ρ 0 •exp( E a /κ B T ) and the fitted results are shown in Figure C. The obtained activation energy E a as a function of x is plotted in Figure D.…”

Effect of Cobalt Doping on the Stability of CaO‐Based Catalysts for Dimethyl Carbonate Synthesis via the Transesterification of Propylene Carbonate with Methanol

“…The high‐resolution Co 2p spectra of the Ca−Co mixed oxide catalysts are deconvoluted into two spin–orbit doublets and three satellite peaks, as shown in Figure 6d. The deconvoluted peaks at 780.3 eV, 796.0 eV and 804.2 eV (the first satellite peak) correspond to Co 2+ ; those peaks at 779.3 eV, 794.5 eV and 789.5 eV (the second satellite peak) correspond to Co 3+ ; and the last satellite peak at 782.1 eV corresponds to Co 4+ [28,47] . The detailed contents of the three types of Co ions are listed in Table 3.…”

Thermoelectric properties of [Ca2CoO3−δ][CoO2]1,62 as a function of Co/Ca defects and Co3O4 inclusions

“…The resistivity decreases a lot compared to the pure sample (up to 23%). Other authors also reported a decrease of the resistivity for the increasing nominal Co content29 from x ¼ 0.565 to x ¼ 0.571 and for the presence of up to 10% Co 3 O 4 impurity 15 below 800 K. Literature indicates15 that a reversal of this anomalous trend happens at a volume fraction of Co 3 O 4 impurities that is much larger than the 1% and 3% studied here (note that the exact value of the critical volume fraction beyond which the reversal is observe seems to vary as a decrease of resistivity was reported for 10% Co 3 O 4 impurity 15 while an increase was found for 7%…”