Enhancement of the thermoelectric figure of merit in n-type Cu_0.008Bi₂Te_2.7Se_0.3 by using Nb doping

Doping with foreign atom has been shown to be an effective way to enhance the dimensionless figure of merit ZT of Bi₂Te₃-based thermoelectric raw materials. Herein, we report that doping with Nb is effective in enhancing the Seebeck coefficient of n-type Cu_0.008Bi₂Te_2.7Se_0.3 polycrystalline bulks. Considering compensation of the Seebeck coefficient due to decrease of the electrical conductivity in Nb-doped compositions, the absolute value of Seebeck coefficient rather increased benefiting from an enhancement of the density of states (DOS) effective mass m* from 1.09m₀ (Cu_0.008Bi₂Te_2.7Se_0.3) to 1.21m₀ − 1.27m₀ (Cu_0.008Bi_2−xNb_xTe_2.7Se_0.3) due to a DOS engineering effect. The values of ZT were 0.84 at 300 K and 0.86 at 320 K for Cu_0.008Bi_1.99Nb_0.01Te_2.7Se_0.3. This compositional tuning approach highlights the possibility of further enhancement of ZT for n-type Bi₂Te₃-based compounds by using a combination of nanostructuring technologies to reduce the thermal conductivity.