Riley Hanus (Northwestern U and ORNL)

October 11, 2019 @ 1:30 pm – 2:30 pm

host: Phil

Title: Heat conduction in defective and complex crystals:  phonon scattering and beyond

Riley Hanus*

* Material Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA

* Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, USA.

The flow of heat through materials is a topic of scientific interest and technological importance in fields of microelectronics, power generation, heat management, and thermoelectrics. For example, advancement in microelectronic technologies (e.g. microprocessors, and high-power electronics) demands ever more efficient removal of the heat generated in these devices. In contrast, technologies such as thermal barrier coatings and thermoelectric materials are designed to stop the flow of heat. In simple, defect-free crystals the thermal conductivity is generally well understood. However, in materials containing defects and/or in those with very complex crystal structures there is a lack of basic understanding which inhibits technological progress.

In this presentation, I will highlight several experimental and theoretical results which aim to establish a fundamental understanding of heat transport in defective materials. First, I will discuss several studies related to heat conduction across interfaces. Secondly, I will demonstrate in several material systems how defects can soften a materials lattice which reduces the phonon group velocity and thus decreases thermal conductivity. Lastly, the transition from crystalline-like to amorphous-like thermal conduction is investigated by studying the lattice dynamics of crystals with very complex crystal structures both computationally and experimentally. Through this analysis emerges a description of phonon transport which is divided between two channels. One is the standard phonon-gas transport mechanism and the other we term the diffuson-channel since it is mathematically the same mechanism in which ‘diffusons’ were defined.

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