Issue 27, 2014

Layered germanium tin antimony tellurides: element distribution, nanostructures and thermoelectric properties

Abstract

In the system Ge–Sn–Sb–Te, there is a complete solid solution series between GeSb2Te4 and SnSb2Te4. As Sn2Sb2Te5 does not exist, Sn can only partially replace Ge in Ge2Sb2Te5; samples with 75% or more Sn are not homogeneous. The joint refinement of high-resolution synchrotron data measured at the K-absorption edges of Sn, Sb and Te combined with data measured at off-edge wavelengths unambiguously yields the element distribution in 21R-Ge0.6Sn0.4Sb2Te4 and 9P-Ge1.3Sn0.7Sb2Te5. In both cases, Sb predominantly concentrates on the position near the van der Waals gaps between distorted rocksalt-type slabs whereas Ge prefers the position in the middle of the slabs. No significant antisite disorder is present. Comparable trends can be found in related compounds; they are due to the single-side coordination of the Te atoms at the van der Waals gap, which can be compensated more effectively by Sb3+ due to its higher charge in comparison to Ge2+. The structure model of 21R-Ge0.6Sn0.4Sb2Te4 was confirmed by high-resolution electron microscopy and electron diffraction. In contrast, electron diffraction patterns of 9P-Ge1.3Sn0.7Sb2Te5 reveal a significant extent of stacking disorder as evidenced by diffuse streaks along the stacking direction. The Seebeck coefficient is unaffected by the Sn substitution but the thermal conductivity drops by a factor of 2 which results in a thermoelectric figure of merit ZT = ∼0.25 at 450 °C for both Ge0.6Sn0.4Sb2Te4 and Ge1.3Sn0.7Sb2Te5, which is higher than ∼0.20 for unsubstituted stable layered Ge–Sb–Te compounds.

Graphical abstract: Layered germanium tin antimony tellurides: element distribution, nanostructures and thermoelectric properties

Supplementary files

Article information

Article type
Paper
Submitted
31 1 2014
Accepted
13 2 2014
First published
13 2 2014
This article is Open Access
Creative Commons BY-NC license

Dalton Trans., 2014,43, 10529-10540

Author version available

Layered germanium tin antimony tellurides: element distribution, nanostructures and thermoelectric properties

S. Welzmiller, T. Rosenthal, P. Ganter, L. Neudert, F. Fahrnbauer, P. Urban, C. Stiewe, J. de Boor and O. Oeckler, Dalton Trans., 2014, 43, 10529 DOI: 10.1039/C4DT00336E

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