Optimization of the thermoelectric properties of Bi₂O₂Se ceramics by altering the temperature of spark plasma sintering

The n-type polycrystalline Bi₂O₂Se ceramics were fabricated by solid state reaction and SPSed at different temperatures (873–973 K). The grains of the sample grow up gradually and the grain size enlarges from about 200 nm to micrometer level with the increase of sintering temperature. The highest electrical conductivity of 6.23 S/cm is obtained for the sample sintered at 898 K which benefits from grain orientation along (00l) plane and the highest measured density. The electrical transport properties tend to decline with further increase of the sintering temperature due to the decrease of density and the orientation degree. The maximum power factor of 78.39 μWK⁻²m⁻¹ is obtained at 773 K. The thermal conductivity is intrinsically suppressed owing to the layered crystal structure of Bi₂O₂Se and fine grains within the nanometer size. The ZT value reaches 0.09 at 773 K for the sample SPSed at 898 K and the optimal temperature during the SPS process has been determined.