Supervisors: Neophytos Neophytou and Gavin Bell

Summary:

Two thirds of all energy used is lost into heat during conversion processes, which puts enormous pressure on energy sustainability. Thermoelectric materials convert waste heat into electricity and can provide solutions towards this problem. Recently, a myriad of materials and compounds with complex electronic structures have been synthesized, offering possibilities for exceptional thermoelectric performance. The project uses Density Functional Theory coupled to advanced electronic transport methods, to examine the potential of the most prominent materials, targeting appropriate electronic structure designs for further optimization. The richness of experimental data, both from literature and in house, will aid towards theory validation.

Background:

The need for energy sustainability and the environmental consequences of fossil fuels make the development of technologies for clean energy imperative. Thermoelectric (TE) materials can harvest enormous amounts of waste heat and convert it into useful electrical power. As 60% of all energy we use is lost into heat during conversion processes, the realization of efficient and scalable TEs can transform the energy-use/savings landscape and play a major role in net-zero sustainability. However, TEs have not found widespread use because of low material efficiencies.

Over the last several years, however, a myriad of complex electronic structure materials and their compounds (Heuslers, silicides, selenides, chalcogenides, etc.) have been synthesized, offering the promise of exceptional performance improvements. In fact, the thermoelectric performance figure of merit, ZT, has been increased from values around 1 (which was the state of the art for 40 years) to values of over 3, making thermoelectrics technologically competitive to allow for large scale exploitation. Two main directions contribute towards this: i) the electronic structures of these materials consist of rich features such as many bands and valleys, elongated shapes and different effective masses, topological features which offer ballistic transport, to name a few; and ii) nanostructuring, with disorder introduced hierarchically at the atomic scale, the nanoscale (<10nm) and the macroscale.

The project uses Density Functional Theory coupled to advanced electronic transport methods, to investigate the electronic and thermoelectric performance of complex electronic structure materials. Through alloying, doping, and nanostructuring, prominent materials will be optimized. The richness of the experimental data in the literature will provide opportunities for theory validation. Experimental measurements and validation for optimal materials which will be identified will also be available through the work of the co-supervisor in Physics who can grow materials using molecular beam epitaxy using a wide range of elements.

Links to HetSys Training:

The project fits naturally within HetSys as develops and utilizes software to describe electronic transport in highly heterogeneous, highly disordered systems (alloys, compounds, hierarchical nanostructures). These by nature involve physics, engineering and computation, as well as the incorporation of uncertainty due to the randomized distribution of grains, surface formation, alloy distributions, etc.

The project is interdisciplinary as it requires the development of a theoretical framework and a simulator that utilizes DFT for the extraction of aspects from the electronic structure of alloys, relevant scattering parameters, and puts them into a form to be used in Boltzmann Transport codes.

The generalized design guidelines developed will guide the next generation of complex band and nanostructured material thermoelectric generators for large power factors.

Uncertainty will be addressed by identifying a few material designs with exceptional performance which can be tested by experiment. Materials from the half-Heusler group, and/or the silicide group will be targeted.