Thermoelectric Properties of Zn Doped BiCuSeO

Layered oxychalcogenide BiCuSeO is a promising thermoelectric material due to its ultra-low thermal conductivity and moderate Seebeck coefficient. The doping of monovalent/divalent elements at the Bi site helps in reducing the electrical resistivity. In this report, Bi1−xZnxCuSeO (x = 0.0, 0.02, 0.04, 0.06, 0.08, and 0.1) was prepared by the solid state synthesis to elucidate the Zn doping effect at the Bi site. Zinc oxide was used as a precursor to dope Zn at the Bi site. The X-ray diffraction patterns were matched with BiCuSeO with no additional peak, which confirms the crystal structure and phase purity of the samples. X-ray photo electron spectroscopy of the Bi0.90Zn0.10CuSeO sample indicated a coexistence of Bi+3 and Bi+4 oxidation states. The electrical resistivity and Seebeck coefficient of the samples decreased with increase in the doping concentration because of increasing carrier concentration. The electrical resistivity of all the doped samples showed a transition from a metallic to semiconducting nature around 473 K. The Seebeck coefficient of the samples with x = 0.06, 0.08 and 0.1 showed a very weak temperature dependence above 523 K, which is a signature of small polaron hopping. The highest power factor of 0.35 mW/m K2 was obtained for x = 0.02 at 773 K. The impedance spectroscopy of the Bi0.90Zn0.10CuSeO sample confirmed the hopping conductivity and also the increase in the mobility of the charge carrier with temperature. The total thermal conductivity was dominated by the lattice thermal conductivity. The highest zT of 0.48 at 773 K has been obtained for x = 0.02, mainly due to the increment in the power factor.