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A3: High temperature materials

 Optimization of synthesis conditions of Na0.75CoO2 for high thermoelectric performance 

Jang-Yeul Tak1,2, Kyu Hyoung Lee3, Jong-Young Kim1, Chang-Hyun Lim1, Won-Seon Seo1, Young Soo Lim1, Hyung Koun Cho2 and Soon-Mok Choi4,*
1 Korea Institute of Ceramic Engineering and Technology, Korea2 Sungkyunkwan Univ., Korea3 Kangwon National Univ., Korea 4 Koreatech, Korea

Reproducibility of phase formation has been an important issue in tailoring electronic and thermal transport properties of NaxCoO2-based thermoelectric materials, however, optimized synthesis conditions for single phase of polycrystalline NaxCoO2 remain unsatisfactory. Here we show that phase formation of Na-Co-O-based system can be controlled by adjusting the reaction temperature. Single phase of Na0.75CoO2 was fabricated by optimized heat treatment for both suppression of Na2O vaporization and CoO phase formation. The largest thermoelectric power factor of the present compound (~5.4 ´ 10-4 W/mK2 at 1173 K) is comparable to that of reported values for single phase polycrystalline NaxCoO2 bulks. In addition, Na0.75CoO2 phase obtained by this approach was confirmed to be stable at high temperatures up to 1000 K.