Thermoelectric properties of ZnO ceramics densified through spark plasma sintering

Thermoelectric properties of pure ZnO ceramics were investigated in this study. ZnO powders were sintered using spark plasma sintering by varying temperature (600–900 °C) and atmosphere (air and vacuum), thereafter, the ceramics were annealed in air at 600 °C. Relative densities >98% were determined for all the samples with grain sizes of the same order of magnitude, hence, thermal conductivity of ~45 W/mK was determined at room temperature. As-sintered ceramics prepared from synthetic powder (CSP) had higher carrier concentration than ceramics prepared from commercial powder (CCP) by 2.3x10¹⁷ cm⁻³. Thus, resistivity and Seebeck Coefficient of 0.08 Ω cm and 475 μV/K were determined, respectively, at room temperature for CSP sintered at 900 °C. There was no significant change on the performance of the ZnO ceramics when the sintering atmosphere and temperature were altered. Annealing did not improve the thermoelectric properties of ZnO ceramics. Maximum ZT of 8x10⁻³ was obtained for CSP sintered at 900 °C.