Nanostructured Heusler Compounds as Model System for Thermoelectrics

A joint research effort between the University of Mainz (Institute of Physics, Prof. Gerhard Jakob), the Max Planck Institue for Chemical Physics of Solids (Prof. Clauda Felser, Dresden), and the University of Stuttgart (Institute for Materials Science, Prof. Anke Weidenkaff, Dr. Benjamin Balke now at TU Darmstadt) is dedicated to the improvement of thermoelectric materials. Thermoelectric generators can convert otherwise wasted heat to useful electrical energy. Waste heat as energy source is abundant in car engines and in power plants. To convert even a small part of this huge energy 'reservoir' to electric energy will reduce greenhouse gas emissions considerably.

Our cooperation is focussed on half-Heusler compounds as model systems for nanostructured thermoelectric materials. In a combined effort of theory and experiment we implement half-Heusler nanostructures by complementary “top down” and “botttom up” approaches. The nanostructured materials are prepared as artificial superlattice structures using a “bottom up” strategy and as spontaneously phase separated bulk materials in a “top down” approach.

The main aim of this investigation is the enhancement of the thermoelectric figure of merit via reduction of the thermal conductivity. As demonstrated in a left figure below, an employment of artificial TiNiSn/HfNiSn superlattices leads to the reduction of the thermal conductivity (black circles) compared to bare materials (blue bars). Interestingly, at the period of 3.2 nm a crossover between the coherent and incoherent phonon transport is observed. It is manifested by a minimum of the thermal conductivity. As expected, reduced thermal conductivity of superlattices improves the thermoelectric figure of merit ZT (right figure below). However, the influence of the interface roughness is complex depending on the length scales of the superlattice and the thickness of the interface with respect to that of the phonons.


Transmission electron microscopy image of superlattices with different degree of tailored interface intermixing

Key publications:

Phonon Bridge Effect in Superlattices of Thermoelectric TiNiSn/HfNiSn With Controlled Interface Intermixing
Sven Heinz, Emigdio Chavez Angel, Maximilian Trapp, Hans-Joachim Kleebe, and Gerhard Jakob,
Nanomaterials 10, 1239 (2020),  doi: 10.3390/nano10061239
Hole Localization in Thermoelectric Half-Heusler (Zr0.5Hf0.5)Co(SbSnx) Thin Films
Sven Heinz, Benjamin Balke, Gerhard Jakob,
Thin Solid Films 692, 137581 (2019),  doi: 10.1016/j.tsf.2019.137581
Subamorphous thermal conductivity of crystalline half-Heusler superlattices,
E. Chavez-Angel , N. Reuter, P. Komar, S. Heinz, U. Kolb, H.-J. Kleebe and G. Jakob,
Nanoscale and Microscale Thermophysical Engineering (2018),
doi: 10.1080/15567265.2018.1505987
Alloy-like behaviour of the thermal conductivity of nonsymmetric superlattices
Emigdio Chavez Angel, Paulina Komar, and Gerhard Jakob,
Nano- and Microscale Thermophys. Eng.21, 287 (2017); doi: 10.1080/15567265.2017.1354106
Tailoring of the electrical and thermal properties using ultra-short period non-symmetric superlattices
Paulina Komar, Emigdio Chávez Ángel, Christoph Euler, Benjamin Balke, Ute Kolb, Mathis M. Müller, Hans-Joachim Kleebe, Gerhard Fecher, and Gerhard Jakob,
APL Mater. 4, 104902 (2016); doi:10.1063/1.4954499
Half-Heusler superlattices as model systems for nanostructured thermoelectrics
Paulina Komar, Tino Jäger, Christoph Euler, Emigdio Chavez Angel, Ute Kolb, Mathis M. Müller, Benjamin Balke, Myriam Haydee Aguirre, Sascha Populoh, Anke Weidenkaff, and Gerhard Jakob,
Phys. Stat. Sol. A 213, 732-738 (10pages)(2016); doi: 10.1002/pssa.201532445
Reduced thermal conductivity of TiNiSn/HfNiSn superlattices
Paulina Hołuj, Christoph Euler, Benjamin Balke, Ute Kolb, Gregor Fiedler, Mathis M. Müller, Tino Jäger, Emigdio Chávez Angel, Peter Kratzer, and Gerhard Jakob,
Phys. Rev. B 92, 125436 (10pages) (2015); doi: 10.1103/PhysRevB.92.125436
Thermal conductivity of half-Heusler superlattices
Tino Jaeger, Christian Mix, Christoph Euler, Paulina Holuj, Myriam Haydee Aguirre, Sascha Populoh, Anke Weidenkaff and Gerhard Jakob,
Semicond. Sci. Technol. 29, 124003 (5pp) (2014),  doi:10.1088/0268-1242/29/12/124003