Thermoelectric properties of Ca sub(3)Co sub(4)O sub(9) ceramics prepared by an alternative pressure-less sintering/annealing method

Nearly dense polycrystalline samples of Ca sub(3)Co sub(4)O sub(9) (CCO) thermoelectric misfit layer cobaltite were prepared by the mixed-oxide route and pressure-less sintering along a two-step sintering protocol. Samples were first sintered at high temperature (e.g. 1200 degree C) to reach a high...

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Bibliographic Details
Published in:Journal of alloys and compounds 2016-02, Vol.659, p.122-126
Main Authors: Schulz, T, Topfer, J
Format: Article
Language:English
Subjects:
Alloys
Annealing
Ceramics
Densification
Phases
Sintering
Sintering (powder metallurgy)
Thermoelectricity
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Summary:Nearly dense polycrystalline samples of Ca sub(3)Co sub(4)O sub(9) (CCO) thermoelectric misfit layer cobaltite were prepared by the mixed-oxide route and pressure-less sintering along a two-step sintering protocol. Samples were first sintered at high temperature (e.g. 1200 degree C) to reach a high degree of densification coupled with complete CCO decomposition into CaO and CoO phases. Subsequent annealing at 900 degree C within the stability range of Ca cobaltite leads to complete re-formation of CCO after 72 h. The samples prepared using this sintering/annealing route exhibit an increased conductivity compared to samples sintered conventionally at 920 degree C. This leads to an enhanced power factor of 170 mu W/(K super(2)m) at 600 degree C. The thermal conductivity of these samples is Kappa = 2.8 W/mK at 100 degree C which is larger as compared to porous and anisotropic conventionally sintered samples. The figure of merit of samples sintered with the proposed sintering/annealing process is ZT = 0.06 at 600 degree C. This process enables simple preparation of dense CCO ceramics as p-type component in thermoelectric generators.
ISSN:0925-8388
DOI:10.1016/j.jallcom.2015.11.001