Thermal transport properties for unveiling the mechanism of BiSbTe alloys in thermoelectric generation: A glance from synchrotron radiation Bi L3-XAFS

Abstract

For thermal to electric energy conversion, designing a high efficiency thermoelectric material entails simultaneously optimizing multiple properties of the material. Although it may appear simple to increase electrical power while minimizing thermal losses, the complicated link between these parameters makes optimization difficult, necessitating a more sophisticated approach. The one-pot zone melting method was used to fabricate undoped and Sb doped Bi2Te3 (Bi2−xSbxTe3; x = 0.0, 0.2, 0.6, and 1.0) in pellets form. X-ray diffraction (XRD), Raman and selected area electron diffraction (SAED) revealed rhombohedral polycrystalline nature and a unique high intensity of the Eg2 optical mode according to the nanosheet nature of the alloys as observed in the scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images. Besides, High Resolution TEM (HRTEM) micrographs depicted twin boundary effect with an angle of 120° for Bi1.8Sb0.2Te3 alloys, which may enhance the electronic transport and the thermoelectric properties of the fabricated compounds. To obtain selective and detailed local structural information of Bi2−xSbxTe3 matrix, synchrotron radiation-based X-ray absorption spectroscopy (XAS) measurements were performed at around Bi L3-edge. A significant influence of the Sb/Bi substitution on the local/atomic structure was observed through the gradual elongation of the average in-plane Bi–Sb bond distance. The combination of different off-line structural characterization techniques such as XRD, Raman, SEM, and HRTEM with synchrotron based XAS technique and Laser-Beam Deflection Spectroscopy (BDS) is necessary to fully describe the samples nature and to get average crystal, morphological and local/electronic structural information for unveiling the BiSbTe mechanism in thermoelectric generation.