Abstract
PbTe-based alloys have the best thermoelectric properties for intermediate temperature applications (500–900 K). We report on the preparation of pristine PbTe and two doped derivatives (Pb0.99Sb0.01Te and Ag0.05Sb0.05Pb0.9Te, so-called LAST18) by a fast arc-melting technique, yielding nanostructured polycrystalline pellets. XRD and neutron powder diffraction (NPD) data assessed the a slight Te deficiency for PbTe, also yielding trends on the displacement factors of the 4a and 4b sites of the cubic Fm-3m space group. Interestingly, SEM analysis shows the conspicuous formation of layers assembled as stackings of nano-sheets, with 20–30 nm thickness. TEM analysis shows intra-sheet nanostructuration on the 50 nm scale in the form of polycrystalline grains. Large numbers of grain boundaries are created by this nanostructuration and this may contribute to reduce the thermal conductivity to a record-low value of 1.6 Wm−1K−1 at room temperature. In LAST18, a positive Seebeck coefficient up to 600 μV K−1 at 450 K was observed, contributing further towards improving potential thermoelectric efficiency.
Highlights
Thermoelectrics can directly convert heat into electrical energy, and their efficiency is evaluated by the figure of merit ZT = S2 σT/κ, where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature, and κ is the total thermal conductivity, which contains the sum of the lattice
We have examined the crystalline powder of our PbTe material with transmission electron microscopy (TEM)
Three thermoelectric materials were prepared by a straightforward arc-melting technique: pristine
Summary
ZT values >1.5 [5,6,7,8] Among all these strategies, nanostructuration is a key role to bear in mind, because it is a useful tool to effectively reduce the thermal conductivity [4,9,10,11], and it has already been used in different chalcogenide-type compounds [12,13]. Tellurium-based compounds are among the most efficient thermoelectric materials, for instance, Bi2 Te3 , is widely used in near room temperature applications [1,14], or GeTe and its alloys [15,16,17,18,19], rare-earth tellurides [20,21,22,23,24], or PbTe [25,26,27,28,29]. PbTe-based thermoelectrics are the best performing materials in the middle-temperature range of 500 to 900 K [1,3,4,30,31], so they are one of Materials 2019, 12, 3783; doi:10.3390/ma12223783 www.mdpi.com/journal/materials
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