The influence of Dy concentration on the thermoelectric properties of n-type Dy-doped Bi₂Te₃ pellets prepared by hydrothermal and carbon burial sintering

Dy-doped Bi₂Te₃ pellets with three different molar ratios between the precursors BiCl₃ and DyCl₃∙6H₂O (x = 0.05, 0.1, and 0.25) were prepared by hydrothermal and carbon burial sintering. The excess of Dy ions in the highly doped samples (x = 0.25) remarkably increased the Seebeck coefficient, reduced the thermal conductivity, and increased ZT more than twofold in the temperature range of 323–375 K compared to pristine Bi₂Te₃. At low Dy concentrations (x = 0.05 and 0.1), the Dy ions substituted the Te_Bi antisites and then intercalated between the Bi₂Te₃ interlayers at higher concentration. The Dy ions act as both the phonon and charge carrier scattering centers which increase the scattering factor and decrease the point defect scattering relaxation time γ. The increase in the number of Te vacancies and the higher sound velocity of Dy (2710 m/s at 20 °C) compared to that of Bi (1790 m/s) considerably contribute to the improvement of the thermoelectric performance of pristine Bi₂Te₃.