Phonon Transport of Disordered Materials with Nanostructures

Phonon engineering of crystalline materials by nanostructures has made great progress in the past decades, and the next non-trivial challenge is how to engineer phonons in disordered materials. We have studied nanostructured amorphous materials such as amorphous superlattices [1] and amorphous phononic crystals (amorphous thin films with holes) [2]. There, by applying the Allen-Feldmann theory, which divided heat carrier into propagons, diffusons, and locons, we found that not only the transport of propagons but also that of diffusons is effectively hindered by the nanostructure interfaces. To gain further direct insight, inelastic x-ray scattering was performed. Partially disordered materials are also of great interest from an academic and industrial point of view. This includes materials consisting of crystalline and amorphous portions, e.g., polycrystals with disordered interfaces. Disordered grain boundaries have been found experimentally to selectively inhibit phonon transport rather than electron transport. Furthermore, a black box model of disordered silicon grain boundaries was successfully performed, revealing that the main structural factors that determine transport are different for phonons and electrons [3]. Crystalline materials with distorted lattices, such as cellulose nanofibers, are also interesting. The thermal conductivity of cellulose nanofibers was found to be greatly enhanced by controlling the arrangement of the constituent cellulose nanofibrils and the hydrogen bonds between the fibrils [4].<br/><br/>[1] Y. Liao, S. Iwamoto, M. Sasaki, M. Goto, J. Shiomi, Nano Energy 84, 105903 (2021).<br/>[2] N. Tambo, Y. Liao, C. Zhou, E. M. Ashley, K. Takahashi, P. F. Nealey, Y. Naito, J. Shiomi, Science Advances 6, eabc0075 (2022).<br/>[3] C. Lortaraprasert, J. Shiomi, npj Computational Materials 8, 219 (2022).<br/>[4] G. Wang, M. Kudo, K. Daicho, S. Harish, B. Xu, C. Shao, Y. Lee, Y. Liao, N. Matsushima, T. Kodama, F. Lundell, L. D. Sooderberg, T. Saito, J. Shiomi, Nano Letters 23, 1144-1151 (2023).