Enhancement of Thermoelectric Properties in Pd–In Co-Doped SnTe and Its Phase Transition Behavior

Abstract

SnTe has attracted more and more attention due to the similar band and crystal structure with high performance thermoelectric materials PbTe. Here, we introduced Pd into SnTe and the valence band convergence was confirmed by first-principles calculation. In the experimental process, we found that Pd-doped SnTe exhibit a reduced thermal conductivity because of softening chemical bonds and grain refining effects. To further improve the thermoelectric performance, Pd–In codoped SnTe samples were prepared, and the abnormal change of thermal conductivity was observed. The results of synchrotron powder diffraction suggest that the local phase transition (local structural distortions) near 400 K results in the first turn on thermal conductivity. Similarly, the second local phase transition in near 600 K observed by neutron powder diffraction lead to a decrease thermal conductivity of the sample. Finally, a peak thermoelectric figure of merit (ZT) ≈ 1.51 has been obtained in Sn0.98Pd0.025In0.025Te at 800 K.

Physical Insights on the Lattice Softening Driven Mid‐Temperature Range Thermoelectrics of Ti/Zr‐Inserted SnTe—An Outlook Beyond the Horizons of Conventional Phonon Scattering and Excavation of Heikes’ Equation for Estimating Carrier Properties

“…Synthesis: The SnTe-based samples were synthesized via a vacuumsealed tube melt processing route. It must be noted that, just like in many other SnTe-based materials that are reported so far, the selfcompensated Sn 1.03-x M x Te (M = dopant) nominal composition was adopted here to reach the actual stoichiometry and to optimize their charge carrier concentration, [37,40,59,64,79,86] that is, to compensate for the inherent nature of SnTe to have Sn vacancies (Sn 1−x Te). From the crystallographic point of view, it was not possible to have excess Sn in the structure (SnTe).…”

“…Though not common, such a phenomenon has been reported in the past for SnTe-based materials. [54,64,93] With the incorporation of Ti/Zr/Mn in SnTe, the red shift/low-frequency shift in the Raman spectra conveys that the force constant of the bonds around the Te site is reduced or the chemical bond is notably softened, as the bond stiffness is inversely proportional to bond length. This softening effect can well explain the reason for decreased lattice thermal conductivity when Ti/Zr or Ti-Mn/Zr-Mn are doped to SnTe.…”

“…Total energy convergence was achieved with a Brillouin zone (BZ) integration mesh of 500 k-points. Supercells of size 2×2×2 consisting of 64 ) were considered, in a way such that they closely represent the experimental compositions. For the purpose of simplicity, though there are some magnetic interactions in the doped samples, the magnetic contribution was not considered in these computations.…”

“…To further support this fact, when the TE properties of pristine SnTe from this work (which contains Sn impurity phase) is compared with some literature reports where they do not detect any Sn secondary phase, their transport properties are quite comparable. [48,64,65]…”

Rare-Earth Nd Inducing Record-High Thermoelectric Performance of (GeTe) 85 (AgSbTe 2 ) 15

“…However, the high toxicity of Pb limits its practical application. Alternatively, κ l of SnTe is relatively higher which leads to lower zT value of only 1.51 at 800 K [23] comparing with PbTe [18] and GeTe [24]. Therefore, nontoxic and highperformance GeTe-based thermoelectric materials, with the peak zT values higher than 2 [24,25], have attracted extensive attention.…”