Abstract
Neutron powder diffraction and thermoelectric characterization of SnSe:Kx intermetallic alloys are presented. Nanostructured ingots were prepared by arc-melting elemental tin and selenium along with potassium hydride. Up to x = 0.1 of K can be incorporated into SnSe. Rietveld refinement of the diffractograms locates potassium on the Sn site in the high-temperature Cmcm structure. However, in the low-temperature Pnma structure, K cannot be localized by difference Fourier maps, indicating the incorporation of K in a disordered form in the interlayer space. STEM-EELS indicates the incorporation of K into the SnSe grains. The resistivity upon K-doping at intermediate temperatures decreases by 1–2 orders of magnitude, but at high temperature is higher than the undoped SnSe. The Seebeck coefficient of K-doped SnSe remains p-type and almost temperature independent (400 μV/K for x = 0.1). The ultralow thermal conductivity of undoped SnSe decreases further upon K-doping to below 0.3 W/m K.
Highlights
Thermoelectric materials hold the promise to help create a greener and eco-friendlier energy economy [1]
The resistivity upon K-doping at intermediate temperatures decreases by 1–2 orders of magnitude, but at high temperature is higher than the undoped SnSe
We observed that below the Pnma-to-Cmcm structural phase transition, K ions cannot be located by diffraction methods, but the conspicuous expansion along the a axis suggests that they are present in the interlayer space, confirmed by Scanning transmission electron microscopy (STEM)-energy loss spectrometer (EELS) spectroscopic images
Summary
Thermoelectric materials hold the promise to help create a greener and eco-friendlier energy economy [1]. Thermoelectrics are typically good semiconductors with large Seebeck coefficient (S), but they need good electrical conductivity (r), which requires a compromise by tuning the Fermi level with chemical doping. Good thermoelectrics extract low thermal conductivity (j), but since the Wiedemann–Franz law connects the electrical conductivity to the electronic thermal conductivity (jel), only the lattice thermal conductivity (jlatt) may be improved independently [2]. Nanostructuring is often the chosen strategy to decrease jlatt and preserve the electronic transport properties S and r [3–8]. In the realm of material science, these competing properties are evaluated in terms of the dimensionless thermoelectric figure of merit zT = T * S2r/(jel ?
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