The influence of Pb/Ag dual doping on the thermoelectric performance of BiCuSeO was investigated. It reveals that the electrical conductivity can be obviously improved owing to the increased carrier concentration mostly caused by the divalent Pb2+ doping at trivalent Bi3+. The electrical conductivity improves from 7.29 S/cm for BiCuSeO to 397.40 S/cm for Pb0.06Bi0.94Cu0.94Ag0.06SeO and Pb0.06Bi0.94CuSeO at 327 K. Combined with the moderate Seebeck coefficient (>120 μV/K) due to the large effective mass, a large power factor with 834 μW/mK2 is achieved. Meanwhile, the lattice thermal conductivity is visibly decreased, mainly benefiting from the substitution of Ag+ at the Cu+ site since the phonon scattering can be enhanced by mass fluctuation and strain fluctuation between the two elements. Thus, the total thermal conductivity is suppressed effectively compared with the Ag-free sample Pb0.06Bi0.94CuSeO. Finally, a maximum ZT value with nearly 1.0 has been obtained for Pb0.06Bi0.94Cu0.94Ag0.06SeO at 873 K, which is ∼64% and ∼47% larger than those of the pristine sample BiCuSeO and Ag-free sample Pb0.06Bi0.94CuSeO. Additionally, the ZT is also larger than the maximum value for the reported Pb-free samples BiCu0.94Ag0.06SeO and Bi0.92Ag0.08CuSeO, suggesting Pb and Ag are effective codopants of BiCuSeO to synergetically tune its electrical and thermal transport properties.
Keywords: BiCuSeO; doping; electrical transport property; thermal conductivity; thermoelectric material.