Journal of Materials Research
November 2005— Volume 20, Number 11

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Thermoelectric properties of CaxCo2O4 aligned crystals M. Shikano and R. Funahashi Research Institute for Ubiquitous Energy Devices, National Institute of Advanced Industrial Science and Technology (AIST), Ikeda, 563-8577 Osaka, Japan M. Kitawaki Osaka Electro-Communication University, Neyagawa, Osaka 572-8530, Japan

Agglomerates of aligned crystals of Ca_xCo₂O₄ with a layer of CoO₂ were grown using a chloride flux technique, and their thermoelectric properties in air were determined. The agglomerates take the form of a very thin flakelike cluster of crystals with a typical size of almost 3 × 2 × 0.07 mm. The values of thermoelectric power along the ab-plane are larger than 200 μV K^-1 at temperatures above 873 K and reach almost 300 μV K^-1 at 973 K. The temperature dependence of the electrical resistivity along the ab-plane shows bends around 450 and 825 K, and the ln ρ_ab-T^-1 curve followed an Arrhenius-type behavior below 450 K. Temperature dependence of thermal conductivity indicated that stacking faults along the c axis induce phonon scattering like that in a misfit-layered structure. The effect of the CoO₂ layer on thermoelectric performance is discussed in comparison with related compounds.

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