Experiments and Modelling of Emerging Energy Materials

PD. Dr. Sebastian Fähler

Leibniz-Institut für Festkörper- und Werkstoffforschung Dresden (IFW) e.V.

10. November 2020, 17.00
WW8, Zoom, Fürth

Emerging energy materials represent a challenge for both, experiments and theory, since at the beginning it is often not clear which material requirements are needed for a particular application and what really happens within a novel functional material. Here we will focus on two examples: thermomagnetic materials for energy harvesting and magnetic shape memory alloys. We will show that the development and application of these emerging energy materials benefit strongly from the combination of experiments and modelling.
In the first part, we address thermomagnetic materials and generators [1]. These allow converting low grade waste heat to electricity, where only a few technologies exist to date. Thermomagnetic generators are one approach proposed more than a century ago. Such devices are based on a cyclic change of magnetization with temperature. This switches a magnetic flux and, according to Faraday’s law, induces a voltage. Here we demonstrate that guiding the magnetic flux with an appropriate topology of the magnetic circuit improves the performance of thermomagnetic generators by orders of magnitude. Through a combination of experiments and simulations, we show that a pretzel-like topology results in a sign reversal of the magnetic flux. This avoids the drawbacks of previous designs, namely, magnetic stray fields, hysteresis and complex geometries of the thermomagnetic material. Our demonstrator, which is based on magnetocaloric plates, illustrates that this solid-state energy conversion technology presents a key step towards becoming competitive with thermoelectric generators.
In the second part we focus on martensitic Heusler alloys, which exhibit excellent thermomagnetic properties and are of particular interest for micro energy harvesting systems. Here, we take on the quest to explain the hierarchically twinned martensitic microstructure occurring in these alloys [2]. For this purpose, five levels have to be solved similar to a computer game. Beginning with the tetragonal unit cell, the correct utilization of twinning is required to construct appropriate building blocks and proceed to the final level. Thereby, the microstructure observed in experiments is successfully explained.

[1] A. Waske et al. Nature Energy 4, 68 (2019)
[2] S. Schwabe et al. Adv. Funct. Mat. accepted (2020)