The thermoelectric properties of sintered bodies of NaCo<SUB>2</SUB>O<SUB>4</SUB>, which is so far the most promising p-type candidate for oxide thermoelectric material, are investigated in terms of their sintering conditions. Double-step sintering, for which single-phase NaCo<SUB>2</SUB>O<SUB>4</SUB> obtained by calcination and sintering with addition of 10% excess of Na each time is re-ground and sintered again, is revealed to attain a marked improvement in the thermoelectric performance of the oxide. The improvement is due to increase in both Seebeck coefficient and electrical conductivity, and is attributed to a distinct enhancement of the two-dimensionality in the crystallites constituting the sintered body. The oxide sintered body consequently attains the figure-of-merit of 0.88×10<SUP>-3</SUP>K<SUP>-1</SUP> at 600°C, and the maximum ZT of 0.78 at 800°C.
|Translated title of the contribution||Microstructures and Thermoelectric Properties of NaCo_2O_4 Prepared by Double-step Sintering|
|Number of pages||6|
|Journal||Funtai Oyobi Fummatsu Yakin/Journal of the Japan Society of Powder and Powder Metallurgy|
|Publication status||Published - Nov 15 2000|