Thermoelectric properties of Bi2Te2.7Se0.3 nanocomposites embedded with MgO nanoparticles

Bi2Te2.7Se0.3 bulk materials containing x vol% MgO nanoparticles (average particle size ≈ 100 nm, x = 0, 0.5, 1.0, 1.5) were synthesized by using high-energy ball milling and plasma- activated sintering (PAS) without any special process for nanoparticle dispersion. A microstructure investigation using a scanning electron microscope (SEM) confirmed that MgO nanoparticles were properly dispersed in the Bi2Te2.7Se0.3 matrix and that the grain size was smaller in MgO-containing samples due to suppressed grain growth. The resistivity and the maximum Seebeck coefficient of Bi2Te2.7Se0.3 increased with increasing MgO content whereas the thermal conductivity decreased in the measurement temperature range of 298 K - 573 K. As a result, the maximum dimensionless figure of merit, ZTmax, increased about 8.5% in this study, from 0.806 for pristine Bi2Te2.7Se0.3 to 0.875 when x = 1.5. The ZTmax was observed to shift to lower temperature, the electron concentration to decrease, and the electron mobility to increase with increasing x, which were explained using a hypothesis that the TeBi antisite defect concentration decreased as the MgO content increased. In summary, the addition of MgO nanoparticles has been shown to be a simple and effective method to improve the low-temperature thermoelectric properties of n-type Bi2Te3 materials.