Enhanced thermoelectric performance of Ca-doped BiCuSeO in a wide temperature range

Abstract

The effect of Ca substitution on microstructure and thermoelectric transport properties of BiCuSeO oxyselenide has been studied. The substitution of Ca2+ for Bi3+ reduces both electrical resistivity and Seebeck coefficient due to an increased carrier concentration. However, the enhanced electrical conductivity compensates for the decrease of Seebeck coefficient, and consequently the power factor is greatly improved in the whole temperature range from 300 to 773 K, exceeding 600 μW m−1 K−2 in the Bi1−xCaxCuSeO samples with 0.075 ≤ x ≤ 0.125. Additionally, the lattice thermal conductivity is significantly reduced due to the refined grains and the introduced point defects that limit the phonon mean free path, resulting in a total thermal conductivity lower than 1.0 W m−1 K−1 in all the doped samples. Benefiting from the enhanced electrical conductivity and the reduced thermal conductivity, high ZT values, both at low and medium temperatures, 0.3 at 300 K and 0.8 at 773 K, are achieved for the Bi0.925Ca0.075CuSeO composition.