BiCuSeO is a promising thermoelectric material not only because of its good thermoelectric properties, but also earth abundant constituents. In this report, Pb and Na have been simultaneously doped at the Bi site of BiCuSeO. Doping Pb is beneficial for the Seebeck coefficient whereas doping Na maintains the hole mobility. Both the dopants increase the carrier concentration and reduce the thermal conductivity by point-defect scattering. The samples with nominal composition Bi0.985-xNa0.015PbxCuSeO (x=0.00, 0.04, 0.06 and 0.08) were prepared using two-step solid-state synthesis. The X-ray diffraction pattern reveals a small amount of Bi2O2.5 phase (<1 vol. %) which is responsible for adversely affecting the electrical conductivity of all the samples. Both the Seebeck coefficient and electrical resistivity decrease with increasing doping fraction due to increasing hole concentration. The highest power factor of 530 μW/mK2 was obtained for Bi0.905Na0.015Pb0.08CuSeO sample at 773 K because of moderate Seebeck coefficient and low electrical resistivity. A low lattice thermal conductivity of 0.37 W/m-K at 773 K was obtained in the Bi0.905Na0.015Pb0.08CuSeO. Due to this low lattice thermal conductivity combined with the high power factor, a zT of 0.63 was obtained for the Bi0.905Na0.015Pb0.08CuSeO sample at 773 K.
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