Group leader

Gudrun Auffermann
Group leader
Phone: +49 351 4646-3201

Heusler compounds

Members

Chenguang Fu
Post-doctoral research scientist
Phone: +49 351 4646-3249

Humboldt Fellowship by Humboldt Foundation in Germany (2016)

Thermoelectrics

Li, Guowei
Guowei Li
Post-doctoral research scientist
Phone: +49 351 4646-3323

Thermoelectrics

Enkhtaivan, Lkhagvasuren
Lkhagvasuren Enkhtaivan
Graduate student
Phone: +49 351 4646-2237

Thermoelectrics

Former Group Members

Berry, Tanya
Tanya Berry
Visiting graduate student

Publication highlights

1.
Elisabeth Rausch, Benjamin Balke, Torben Deschauer, Siham Ouardi, and Claudia Felser, "Charge carrier concentration optimization of thermoelectric p-type half-Heusler compounds," APL Materials 3 (4), 1-8 (2015).
2.
J. Krez, B. Balke, S. Ouardi, S. Selle, T. Höche, C. Felser, W. Hermes, and M. Schwind, "Long-term stability of phase-separated half-Heusler compounds," Physical Chemistry Chemical Physics 17 (44), 29854-29858 (2015).
3.
Siham Ouardi, Gerhard H. Fecher, Benjamin Balke, Xenia Kozina, Gregory Stryganyuk, Claudia Felser, Stephan Lowitzer, Diemo Ködderitzsch, Hubert Ebert, and Eiji Ikenaga, "Electronic transport properties of electron- and hole-doped semiconducting C1b Heusler compounds: NiTi1-xMxSn (M=Sc, V)," Physical Review B 82 (8), 1-9 (2010).

Collaboration

Dr. Benjamin Balke

Johannes Gutenberg University, Mainz, Germany

website

PD Dr. Thomas Gruhn

Material- und Prozesssimulation, Universität Bayreuth

website

Thermoelectrics

Thermoelectric (TE) materials yield the direct transformation of waste heat into useful electricity. TE devices are composed on pairs of n-type and p-type materials.

Thermoelectric (TE) materials yield the direct transformation of waste heat into useful electricity. TE devices are composed on pairs of n-type and p-type materials. The efficiency of a TE material is characterized by its dimensionless figure of merit zT:

zT =S2T
ρκ

where S is the Seebeck coefficient (also known as the thermopower), r the electrical resistivity, k the thermal conductivity, and T the absolute working temperature.

Intermetallic half-Heusler compounds with a general formula XYZ (X, Y = transition metals; Z = main group such Sn or Sb) crystallizing in the cubic MgAgAs-type structure (Figure 1) have attracted considerable attention as suitable TE materials because of their very flexible electronic structure.

<p style="text-align: justify;"><strong>Figure 1:</strong> <em>Half-Heusler structure with general composition XYZ (C1<sub>b</sub> or MgAgAs structure type) crystallizing in the cubic space group F43m (216)).</em></p> Zoom Image

Figure 1: Half-Heusler structure with general composition XYZ (C1b or MgAgAs structure type) crystallizing in the cubic space group F43m (216)).

Narrow band gap semiconducting C1b Heusler compounds such as TiNiSn and CoTiSb are deal materials for new thermoelectric modules. These compounds show high figure of merit (ZT>1), are available as p- and n-type (Figure 2) semiconductors, cheap and nontoxic. 

Narrow band gap semiconducting C1b half-Heusler compounds with 18 valence electrons in the primitive cell, such as TiNiSn and TiCoSb are deal materials for new thermoelectric modules. These narrow-band-gap compounds were reported to exhibit excellent thermoelectric properties due to wide possibilities of modifying their electronic properties by partial substitution or doping.

Substitution on the main group site Z provides charge carriers, where the substitution on the X or Y site causes mass fluctuation disorder that lead to a reduction in thermal conductivity.

Particularly, isoelectronic partial substitutions of Ti with its heavier homologues Zr or Hf achieve an intrinsic phase separation of the half-Heusler compounds.

There are no currently available thermoelectric materials that fulfil all of these requirements. However, C1b Heusler materials do meet nearly all of the requirements, including a high power factor.

<div style="text-align: justify;"><strong>Figure 2:</strong> <em>Thermoelectric properties of the p-type half-Heusler compound Ti<sub>0.3</sub>Zr<sub>0.35</sub>Hf<sub>0.35</sub>CoSb<sub>1−x</sub>Sn<sub>x</sub> as a function of the carrier concentration n at 610°C [1].</em></div> Zoom Image
Figure 2: Thermoelectric properties of the p-type half-Heusler compound Ti0.3Zr0.35Hf0.35CoSb1−xSnx as a function of the carrier concentration n at 610°C [1].

 
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