Lattice Softening Significantly Reduces Thermal Conductivity and Leads to High Thermoelectric Efficiency

Riley Hanus, Matthias T. Agne, Alexander J.E. Rettie, Zhiwei Chen, Gangjian Tan, Duck Young Chung, Mercouri G. Kanatzidis, Yanzhong Pei, Peter W. Voorhees, G. Jeffrey Snyder*

*Corresponding author for this work

Research output: Contribution to journalArticle

17 Scopus citations

Abstract

The influence of micro/nanostructure on thermal conductivity is a topic of great scientific interest, particularly to thermoelectrics. The current understanding is that structural defects decrease thermal conductivity through phonon scattering where the phonon dispersion and speed of sound are assumed to remain constant. Experimental work on a PbTe model system is presented, which shows that the speed of sound linearly decreases with increased internal strain. This softening of the materials lattice completely accounts for the reduction in lattice thermal conductivity, without the introduction of additional phonon scattering mechanisms. Additionally, it is shown that a major contribution to the improvement in the thermoelectric figure of merit (zT > 2) of high-efficiency Na-doped PbTe can be attributed to lattice softening. While inhomogeneous internal strain fields are known to introduce phonon scattering centers, this study demonstrates that internal strain can modify phonon propagation speed as well. This presents new avenues to control lattice thermal conductivity, beyond phonon scattering. In practice, many engineering materials will exhibit both softening and scattering effects, as is shown in silicon. This work shines new light on studies of thermal conductivity in fields of energy materials, microelectronics, and nanoscale heat transfer.

Original languageEnglish (US)
Article number1900108
JournalAdvanced Materials
Volume31
Issue number21
DOIs
StatePublished - May 24 2019

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Keywords

  • lattice dynamics
  • thermal conductivity
  • thermoelectrics

ASJC Scopus subject areas

  • Materials Science(all)
  • Mechanics of Materials
  • Mechanical Engineering

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