Structural Evolution from Neutron Powder Diffraction of Nanostructured SnTe Obtained by Arc Melting

Abstract

Among chalcogenide thermoelectric materials, SnTe is an excellent candidate for intermediate temperature applications, in replacement of toxic PbTe. We have prepared pure polycrystalline SnTe by arc melting, and investigated the structural evolution by temperature-dependent neutron powder diffraction (NPD) from room temperature up to 973 K. In this temperature range, the sample is cubic (space group Fm-3m) and shows considerably larger displacement parameters for Te than for Sn. The structural analysis allowed the determination of the Debye model parameters and provided information on the Sn–Te chemical bonds. SEM images show a conspicuous nanostructuration in layers below 30 nm thick, which contributes to the reduction of the thermal conductivity down to 2.5 W/m·K at 800 K. The SPS treatment seems to reduce the number of Sn vacancies, thus diminishing the carrier density and increasing the Seebeck coefficient, which reaches 60 μV K−1 at 700 K, as well as the weighted mobility, almost doubled compared with that of the as-grown sample.

Keywords

• thermoelectrics
• neutron powder diffraction
• Ge deficiency
• structural phase transition