Improved figure of merit and other thermoelectric properties of Sn1−xCuxSe

Abstract

With an intention of improving the figure of merit (ZT) of SnSe, we substitute up to 10% of Cu in place of Sn in SnSe. After confirming the phase purity, crystal structure, and stoichiometry of the prepared compositions using X-ray diffraction and energy dispersive spectroscopy, the microstructure was examined by field emission scanning electron microscopy. Thorough examination of the transport properties in the temperature range of 5–400 K was undertaken. In particular, four-probe electrical resistivity, Hall effect, Seebeck coefficient, and thermal conductivity were recorded for all compositions. Heat capacity was also measured. The results show peculiar nature of Sn1−xCuxSe; a small percentage of Cu addition acts as an annihilation center for the holes in SnSe. But as the substitution percentage is increased, the electrons contributed by the d-band of Cu seem to add a sizable concentration of charge carriers at the Fermi level which affects its transport properties. However, the p-type nature of conduction in SnSe does not change. Owing to the increased participation of electrons in the conduction process, a maximum carrier concentration of 1.12 × 1018 cm−3 (10% Cu-substitution) is observed. Thermopower can no longer be attributed to a single parabolic band structure for the Sn1−xCuxSe series. Interestingly, the thermal conductivity and heat capacity values remain nearly unchanged. With an improvement in the value of ZT (1.02 at 300 K) and compatibility factor of ≤2, we find that replacing a small percentage of Sn with Cu can be a good alternative to improve the performance of polycrystalline SnSe.