Augmentation of the thermoelectric properties of polycrystalline Tin selenides via formation of SnSe/SnSe2 composites

With a purpose of simultaneously enhancing the thermoelectric properties of polycrystalline tin selenides, composites of SnSe/SnSe2 have been obtained. Starting with a synthesis of the [Sn + (x + 1) . Se] mixtures for different x values, composites with up to 65:35 ratio of the two phases have been synthesized. X-ray diffraction and Raman spectroscopy confirm the formation of two distinctively different crystal structures in the composite. Upon inspection of optical, electronic, and thermoelectric properties, the composites are found to exhibit emergent properties that are an improvement over its individual phases. Changes associated with dominance of one phase over the other are noticed in the valence band spectra obtained using X-ray photoelectron spectroscopy. With the change in ratio of SnSe:SnSe2 phase, a considerable change is seen in the thermal conductivity (kappa). The change in kappa is due to decrease in the phonon mean free path that happens due to scattering of phonons at the grain boundaries of the two phases.