Thermoelectric properties of Ca₃Co₄O₉ ceramics

Abstract

Ca₃Co₄O₉ ceramics were prepared using the sol-gel process with ordinary pressing sintering and their thermoelectric properties were measured from room temperature to 673 K. The experimental results show that single phase Ca₃Co₄O₉ can be fabricated at 750–900 °C in different citrate acid molar proportions for 0.2–1.0. For all the oxides, both the Seebeck coefficients S and the electrical conductivities κ increase with the increasing temperature. The Seebeck coefficients S are all positive. The thermal conductivities k increase with the increasing temperature also and the lattice thermal conductivity κ _l plays an important role to the thermal conductivity κ. The citrate acid molar proportions have a large influence on the particle sizes, which influences the thermoelectric properties of the ceramics. The figure of merit increases with the increasing temperature and reaches 4.5×10⁻⁵ K⁻¹ at 573 K for the sample in the citrate acid molar proportion of 0.46.

Keywords

cobaltite ceramic / thermoelectric properties / sol-gel method

References

[1] Terasaki I., Sasago Y., Uchinokura K. Large Thermoelectric Power in NaCo₂O₄ Single Crystals[J]. Phys. Rev. B, 1997, 56(33): R12685-12687.

[2] Ray R., Ghoshray A., Ghoshray K. ⁵⁹Co NMR Studies of Metallic NaCo₂O₄[J]. Phys. Rev. B, 1999, 59(14): 9454-9461.

[3] Seetawan T., Amornkitbamrung V., Burinptakhon T., . Thermoelectric Properties of Na_xCo₂O₄/Ag Composites[J]. J. Alloy Compd., 2006, 144(1–2): 293-297.

[4] Masset A. C., Michel C., Maignan A., . Misfit-layered Cobaltite with An Anisotropic Giant Magnetoresistance: Ca₃Co₄O₉[J]. Phys. Rev. B, 2000, 62(1): 166-175.

[5] Morita y., Poulsen J., Sakai K., . Oxygen Nonstoichiometry and Cobalt Valence in Misfit-layered Cobalt Oxides[J]. J. Solid State Chem., 2004, 177(9): 3149-3155.

[6] Takeuchi T., Kondo T., Soda K. Electronic Structure and Large Thermoelectric Power in Ca₃Co₄O₉[J]. J. Electron Spectrosc. Relat. Phenom., 2004, 137–140: 595-599.

[7] Mikami M., Ando N., Funahashi R. The Effect of Ag Addition on Electrical Properties of the Thermoelectric Compound Ca₃Co₄O₉[J]. J. Solid State Chem., 2005, 178(7): 2186-2190.

[8] Min X.-m., Xing X.-ling. Electronic Structure and Thermoelectric Properties of Ca₃Co₄O₉[J]. J. Wuhan Uni. Tech.-Mat. Sci. Ed., 2006, 21(1): 13-15.

[9] Liu H. Q., Zhao X. B., Zhu T. J., . Thermoelectric Properties of Gd, Y Co-doped Ca₃Co₄O_9+δ[J]. Curr. Appl. Phys., 2009, 9(2): 409-413.

[10] Iwasaki K., Yamane H., Kubota S. Power Factors of Ca₃Co₂O₆ and Ca₃Co₂O₆-based Solid Solutions[J]. J. Alloy Compd., 2003, 358(1–2): 210-215.

[11] An J.-m., Min X.-m., Chen S.-l., . Thermoelectric Properties and Electronic Structure of Ca₃Co₂O₆[J]. J. Wuhan Uni. Tech.-Mat. Sci. Ed., 2004, 19(4): 46-48.

[12] Mikami M., Funahashi R. The Effect of Element Substitution on High-temperature Thermoelectric Properties of Ca₃Co₂O₆[J]. J. Solid State Chem. Compounds, 2005, 178: 1670-1674.

[13] Yamada K., Honda Z., Luoa J., . Field Induced Spin Transitions and Large Magnetoresistance in the Quasi-one- dimensional Magnet Ca₃Co₂O₆[J]. J. Alloy Compd., 2006, 423(1–2): 188-190.

[14] Funahashi R., Matsubara I. Thermoelectric Properties of Pb- and Ca-doped (Bi₂Sr₂O₄)_xCoO₂ Whiskers[J]. Appl. Phys. Lett., 2001, 79(3): 362-364.

[15] Fujii T., Terasaki I., Watanabe T., . In-plane Anisotropy on the Transport Properties in the Modulated Bi₂O₂-based Conductors Bi-2212 and Bi-Sr-Co-O[J]. Phys. C: Superconductivity Part 1, 2002, 378–381: 182-186.

[16] Zhu P. W., Imai Y., Isoda Y. Composition-dependent Thermoelectric Properties of PbTe Doped with Bi₂Te₃[J]. J. Alloy Compd., 2006, 420(1–2): 233-236.

[17] Zhao L. D., Zhang B. P., Li J. F., . Enhanced Thermoelectric and Mechanical Properties in Textured n-type Bi₂Te₃ Prepared by Spark Plasma Sintering[J]. Solid State Sci., 2008, 10(5): 651-658.

[18] Kuo Y. K., Sivakumar K. M. Thermoelectric Properties of the CoSi_1−x Ge_x Alloys[J]. J. Appl. Phys., 2005, 98: 123510-1-123510-5.