Enhancing effects of Te substitution on the thermoelectric power factor of nanostructured SnSe_1-xTe_x

Nanostructured SnSe1-xTex (0 < x < 0.2) was prepared by the planetary ball milling method. The prepared materials were studied by various analytical techniques. XRD analysis shows the pure phase of SnSe when x ≤ 0.1 and the secondary phase of SnTe was observed when x ≥ 0.1, possibly due to the low solid solubility limit of Te in SnSe. FESEM images revealed that the grain sizes of all the samples were in the range of 100 to 500 nm. TEM images showed the grain structures, sizes and grain boundaries of the samples. XPS analysis confirmed the incorporation of Te in SnSe1-xTex and the binding states of the elements in the samples. The samples were made into pellets and sintered at high temperature. The electrical resistivity of the SnSe1-xTex pellets decreased by up to two orders of magnitude as the x value increased in the samples. Concomitantly, the Seebeck coefficient of the SnSe1-xTex samples decreased drastically as the x value increased in the samples. A power factor (PF) of 102.8 μW K-2 m-1 was obtained for the SnSe0.9Te0.1 sample at 550 K, which is higher than the reported values for SnSe and SnSe1-xTex. When substituting Se with Te, the band structure of SnSe changes, which significantly enhances the thermoelectric PF of SnSe1-xTex for x ∼ 0.1. The PF decreased when the x value was increased further (x ≥ 0.1), possibly due to the precipitation of the SnTe phase. These experimental results demonstrate that the addition of a reasonable amount of Te is a promising approach for improving the thermoelectric properties of SnSe.