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 Bi2-xPbxTe3 (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 κlat 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 Bi1.99Pb0.01Te3 (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.