Riley Hanus, Janine George, Max Wood, Alexander Bonkowski, Yongqiang Cheng,Douglas L. Abernathy, Michael E. Manley, Geoffroy Hautier, G. Jeffrey Snyder, and Raphael P. Hermann Materials Today Physics (2020)
Recently density functional theory (DFT) based two-channel lattice dynamics (LD) has emerged as a powerful tool to predict the thermal conductivity of materials ranging from crystalline to disordered. Within this framework, heat conduction can be thought of transporting through (i) the common phonon-gas channel (diagonal) and (ii) the diffuson channel (off-diagonal), which combine additively. We show how two channel LD predicts that the diffuson channel dominates in thermoelectric Yb14(Mg,Mn)Sb11 above room temperature. More importantly we demonstrate how this tool can provide rational design principles for the diffuson channel and therefore provides a clear avenue to engineer the thermal conductivity of disordered and amorphous materials.
Riley Hanus, Matthias T. Agne, Alexander J. E. Rettie, Zhiwei Chen, Gangjian Tan, Duck Young Chung, Mercouri G. Kanatzidis, Yanzhong Pei, Peter W. Voorhees, and G. Jeffrey Snyder. Advance Materials (2019)
Two fundamentally different avenues for controlling thermal conductivity are phonon scattering and lattice softening, or the reduction of phonon speed. The latter mechanism is particularly attractive when phonon-phonon scattering is inherently very strong, such as in thermoelectric materials and/or at high temperatures. In this work we show the importance of lattice softening in two specific cases, PbTe and nanocrystalline Si. We have affectionately named this project 'The Bird' since when a phonon dispersion softens it looks like a bird flapping its wings.
Riley Hanus, Anupam Garg, G. Jeff Snyder. Comms. Phys. (2018)
Thermal resistance across interfaces and grain boundaries is an inherently complex topic. It is widely accepted that the structure of the interface at the nanoscale is critically important when describing phonon transmitance and reflectance. Many boundaries in cyrstalline materials can be described as arrays of linear defects. This paper presents several phyiscal mechanisms that arrise when considering such a structure. An analytical theory is presented to describe phonon grain boundary scattering/transmisivity which contains information about the nanoscale structure of the interfaces.
Riley Hanus, Xingyu Guo, Yinglu Tang, Goudong Li, G. Jeff Snyder, Wolfgang G. Zeier. Chem. Mat. (2017)
As was identified by Yinglu Tang et el. the electronic origin of the superior thermoelectric properties is attributed to a secondary conduction band with 12 carrier pockets. Using a combined computational and experimental approach the chemical nature of critical features in the band structure are highlighted. Synchrotron diffraction and refinement studies reveal interesting structural behavior upon doping and upon heating. The work of Korotaev and Yanilkin supplements this study nicely, and identifies that electron-phonon interactions are indeed required to explain the experimentally observed band convergence with temperature.
Peng-an Zong*, Riley Hanus*, Maxwell Dylla, Yunshan Tang, Jingcheng Liao, Qihao Zhang, G. Jeff Snyder and Lidong Chen. Energy Environ. Sci. (2016) *contributed equally
Incorporating 2D materials into the grain-boundary complexion can modify transport across the grain boundary (GB) in fundamentally different ways than traditional GB phases. We find that wrapping the grains of skudderudite with several layers of graphene dramatically increases the thermal boundary resistance while hardly effecting the electrical properties. This effect was observed in both n and p-type skutterudite and the resulting 16 TE module exhibited a 24% increase in conversion efficiency due to this GB engineering.
Matthias T. Agne, Riley Hanus, G. Jeff Snyder. Energy Environ. Sci. (2018)
Estimating how low the thermal conductivity can be engineered can set practical limits for a variety of applications. A model for the thermal conductivity of bulk solids is proposed in the limit of diffusive transport mediated by diffusons as opposed to phonons is presented.
Gangjian Tan, Shiqiang Hao, Riley Hanus, et al. ACS Energy Let. (2018)
In this collaboration between the Kanatzidis, Wolverton, Snyder and Dravid groups, we report on the underlying mechanisms that enable the SnTe−AgSbTe2 system to exhibit superior thermoelectric figure of merit (zT ) compared to its parent compound SnTe. Specifically, alloying with Ag and Sb on the Sn site promotes the formation of cation vacancies which softens the materials lattice slowing the propagation of phonons while also inducing phonon scattering.
The goal of this five part lecture series is to establish a working knowledge of thermal transport theory at the nano-scale. After this course the participants will have the requisite knowledge to interpret current research in the computational, theoretical, and experimental thermal sciences. Additionally, they will have the foundation required to begin building thermal transport models which are useful in guiding independent research and interpreting results.
Time: 1:30pm to 2:30pm
Dates and locations: (1) Feb. 17th MRDC 3515 (2) Feb. 24th MRDC 3515 (3) Mar. 2nd Student Center 332 (4) Mar. 9th MRDC 3515 (5) Mar. 16th MRDC 3515
Sonal Rangnekar, Riley Hanus*. MRS bulletin (March 2019). * 2018 Weertman Fellowship recipient.
Article published recounting the Symposium in Honor and Remembrance of Johannes (Hans) and Julia Weertman, held November 16 in Evanston, Ill.