Enhanced thermoelectric transport properties of Bi₂Te₃ polycrystalline alloys via carrier type change arising from slight Pb doping

Herein, thermoelectric transport properties of lightly Pb-doped Bi_2-xPb_xTe₃ (x = 0, 0.0025, 0.005, and 0.01) alloys are investigated. Negative Seebeck coefficient (−169 μV/K) of the pristine Bi₂Te₃ increases to −120 μV/K for x = 0.0025 at 300 K. As Pb further doped, positive Seebeck coefficients of 191 and 157 μV/K are measured for x = 0.005 and 0.01, respectively. P-type power factor increased to 2.32 mW/mK² by the Pb doping for x = 0.01 at 300 K, compared with n-type power factor of 1.81 mW/mK² of the pristine Bi₂Te₃. The decrease in κ_lat was observed for x = 0.01 due to additional phonon scattering by point defects. As results, p-type thermoelectric figure of merit zT of 0.42 for x = 0.01 is achieved compared with n-type zT of 0.35 for Bi₂Te₃ at 300 K. The maximum p-type zT of 0.56 was obtained for Bi_1.99Pb_0.01Te₃ (x = 0.01). Therefore, a relative high p-type zT value was successfully achieved by the slight Pb doping in Bi₂Te₃ by carrier type change from n-type to p-type.