Preparation and thermoelectric properties of grain aligned (Ca,Bi)/sub 3/Co/sub 4/O/sub 9/ ceramics

Effects of sintering process on the thermoelectric properties of (Ca,Bi)/sub 3/Co/sub 4/O/sub 9/ ceramics have been investigated. We have prepared (Ca, Bi)/sub 3/Co/sub 4/O/sub 9/ bulk materials using the methods of spark plasma sintering (SPS), hot pressing (HP), and a combination of them. Power factors of the SPS and HP samples at 700/spl deg/C are 4.2/spl times/10/sup -4/ Wm/sup -1/ K/sup -2/ and 4.5/spl times/10/sup -4/ Wm/sup -1/ K/sup -2/, respectively. The combination of SPS and HP enables bulk ceramics (SPS-HP) to be high density, grain alignment, and low resistivity without any degradation of the thermoelectric power. The power factor and figure of merit of the SPS-HP sample attain to 5.7/spl times/10/sup -4/ Wm/sup -1/ K/sup -2/ and ZT=0.29 at 700/spl deg/C, respectively.