To produce electricity, thermoelectric materials capture waste heat from sources such as automobile exhausts or industrial processes. Improving the materials' efficiency will require further reduction of thermal conductivity. A new article from a Georgia Institute of Technology professor clarifies common challenges involved in thermal transport.

Recent research has focused on the possibility of using interference effects in phonon waves to control heat transport in materials. Wave interference is already used to manage electronic, photonic, and acoustic devices. Thermal transport could similarly facilitate development of more efficient thermoelectric and nanoelectronic devices, improved thermal barrier coatings, and new materials with low thermal conductivity.

The new article, published in the journal Nature Materials, describes recent developments and predicts future advances in phonon wave interference and thermal bandgap materials.

“If you can make heat behave as a wave and have interference while controlling how far it moves, you could basically control all the properties behind heat transport,” said Martin Maldovan, an assistant professor in the School of Chemical and Biomolecular Engineering and School of Physics at the Georgia Institute of Technology, and the paper’s author. “This would be a completely new way to understand and manipulate heat.”

Until now, heat transport in nanostructured materials has largely been controlled by introduction of atomic-scale impurities, interfaces, surfaces, and nanoparticles that reduce heat flow and scatter the phonons diffusely. Controlling wave effects could facilitate new approaches involving the specular reflection and transmission of thermal vibrations at interfaces.

The search for thermal phononic wave materials will focus on semiconductors much like those used in microelectronics, Maldovan said. Likely materials include silicon-germanium, gallium and aluminum arsenide and certain oxide superlattices.