Magnèli phase TinO2n-1 bulks prepared by SPS followed by carbon reduction and their thermoelectric performance

Abstract

We fabricated Magnèli phase TinO2n-1 compacts from nano-sized rutile TiO2 powder by spark plasma sintering (SPS) followed by carbon reduction at elevated temperatures. These compacts were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD results showed that the n value in Magnèli phase TinO2n-1 mainly depended on the reduction temperature and holding time. Higher reduction temperature or longer holding time favored to smaller n value through withdrawing more oxygen atoms from the lattice of TiO2. Meanwhile, the thermoelectric properties including electrical resistivity, thermal conductivity, Seebeck coefficient, power factor and ZT value of these compacts were measured or calculated. The electrical conductivity was greatly improved while Seebeck coefficient still kept rather large values, which resulted in an extremely high value of power factor at elevated temperature. The highest power factor reached 6.5 × 10−4 W m−1 K−2 at 973 K and the greatest ZT value ran up to 0.1 at 873 K.