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Condensed Matter and Complex Systems

EPJ B Colloquium - Hierarchically nanostructured thermoelectric materials: challenges and opportunities for improved power factors

Schematic of a hierarchically nanostructured thermoelectric material consisting of a matrix material with embedded atomic defects, nanoinclusions (NIs), and grain boundaries. Phonons scatter of the defects. Such geometry also provides possibilities for power factor improvements.

The field of thermoelectric materials has undergone a revolutionary transformation over the last couple of decades as a result of the ability to nanostructure and synthesize myriads of materials and their alloys. The ZT figure of merit, which quantifies the performance of a thermoelectric material has more than doubled after decades of inactivity, reaching values larger than two, consistently across materials and temperatures. Central to this, is the drastic reduction in the materials’ thermal conductivity due to the hierarchical scattering of phonons on the purposely included numerous interfaces, boundaries, dislocations, point defects, phases, etc. However, as the thermal conductivity has reached amorphous values, these benefits are reaching their limits. Any further benefits would come from the power factor, namely the product of the electronic conductivity and Seebeck coefficient squared. These quantities need to be maximized, however, they are in general inversely related, which makes power factor improvement a significant challenge.

In a new Colloquium published in EPJ B, an international author team review recent efforts undertaken in the same ultra-low thermal conductivity nanostructured materials, but now focusing on power factor improvements. They then explore how to design and optimize nanostructured materials in order to relax the adverse interdependence of the electrical conductivity and Seebeck coefficient. For this, elegant designs are presented, reached through advanced simulations and partially backed by experiments, which identifies the essential design ‘ingredients’ for exceptionally high thermoelectric power factors. The combination of the existing methods for ultra-low thermal conductivities and the presented methods for ultra-high power factors, could provide the leap forward for thermoelectric materials.

E. Hernandez and H. Rieger
I am naturally indebted to you and the referees who contributed to this success with your time and constructive advice.

Hamid Assadi

ISSN (Print Edition): 1434-6028
ISSN (Electronic Edition): 1434-6036

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