CENIDE: News

Thermoelectric generators made from polar oxide nano-layers
(c) CENIDE, AG Pentcheva

Energy Recuperation

Thermoelectric generators made from polar oxide nano-layers

[16.03.2017]

Whether coating hot pipework in industrial applications or sitting in the exhausts of our cars, thermoelectric generators utilise thermal gradients to generate electricity, retaining energy that would otherwise be lost. Unfortunately, many of the materials currently used for this purpose are rare, toxic, or sometimes even both. But thanks to the work of scientists at the Center for Nanointegration (CENIDE) at the University of Duisburg-Essen (UDE), this may soon no longer be the case, as they have applied for a patent for technology which harnesses nano-layers with charged surfaces.

For a thermoelectric generator to work, one of its sides must be as hot as is possible, while the other side remains cold. As a result, they need to conduct very little heat, while being excellent conductors of electricity – two properties which seldom go hand in hand. Yet theoretical physicists Prof. Rossitza Pentcheva and Dr Benjamin Geisler have shown that a heterostructure comprising extremely thin layers of lanthanum nickelate and strontium titanate can do just that. The perovskites are grown epitaxially, layer by layer, with the resulting material all but entirely composed of charged interfaces that are only a nanometre apart.

Unlike traditional semiconductors, these oxide heterostructures remain stable even at high temperatures and are constructed from non-toxic materials. Furthermore, the layer structure scatters the phonons and reduces the thermal conductivity of the lattice in the perpendicular direction, whilst simultaneously leading to increases in the Seebeck coefficient.

The real triumph of this research is that while, traditionally, two different materials are used – one of which is negative (the n-type) and the other is positively doped (the p-type) – Pentcheva and Geisler have proven that both types can be produced from the same combination of materials, simply by changing the order of the layers where the surfaces meet. To this end, the scientists carried out material-specific quantum theory simulations, calculating the thermoelectric properties of the heterostructures according to the results. As reported in the March issue of the journal Physical Review B, Pentcheva concludes that ‘the p-type is already highly efficient, and the n-type can be optimised through additional modifications.’ She continues ‘the wide-ranging variability of the cations in these oxides provides a playing field in which further material combinations and improved properties can be identified according to the same concept.’

‘The materials used for p and n-types are often structurally or electronically incompatible,’ explains Geisler. ‘Thus, it was a totally new approach to construct both variants from the same material.’ By doing so, the scientists have proved for the first time that their layer concept works and could render expensive, harmful materials surplus to requirements.

 

Caption: The construction of the oxide heterostructures of the n-type (left) and the p-type (right). The blue, orange and small red balls represent La, Sr and O ions, while brown and bark blue octahedra are centred around the Ti and Ni ions.

Original publication: B. Geisler, A. Blanca-Romero, and R. Pentcheva: ‘Design of n- and p-type oxide thermoelectrics in LaNiO3/SrTiO3(001) superlattices exploiting interface polarity’, Physical Review B 95, 125301 (2017)

DOI: 10.1103/PhysRevB.95.125301

Further information:
Prof. Rossitza Pentcheva, 0203 379-2238, rossitza.pentcheva@uni-due.de

Editor: Birte Vierjahn, 0203/ 379-8176, birte.vierjahn@uni-due.de