Crystal Growth of Thermoelectric Material Na_xCoO_<2-δ> by a Flux Method : Structure and Mechanical and Thermal Properties of Condensed Matter

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Na_xCoO_<2-δ> (0.5≤x≤1) crystals were grown by a flux method. The largest Na_xCoO_<2-δ> crystal size was 10×10×0.5mm^3, and the crystal phase depended on the composition of the flux. Crystals grown from a flux of NaCl mixed with Na_2CO_3 and B_2O_3 and crystals grown from a flux of Na_2CO_3 mixed with B_2O_3 were identified as Na_<0.6>CoO_<2-δ> (γ phase) and Na_<0.9>CoO_<2->δ (α phase), respectively. The structures and compositions of these crystal growths were determined with a powder X-ray diffraction device and an energy dispersive X-ray spectrometer, respectively. The in-plane thermoelectric power values of these two types of crystal increased with temperature and reached 96_μV/K and 87_μV/K at 450K, respectively.
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2002-07-01