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 language | English (US) |
|---|---|
| Article number | 1900108 |
| Journal | Advanced Materials |
| Volume | 31 |
| Issue number | 21 |
| DOIs | |
| State | Published - May 24 2019 |
Funding
R.H. acknowledges support from the Johannes and Julia Randall Weertman Graduate Fellowship. M.T.A. acknowledges support from the PPB Graduate Fellowship. G.J.S. and M.T.A. acknowledge thermoelectrics research at Northwestern University through the Center for Hierarchical Materials Design (CHiMaD). R.H. would like to thank Christos Malliakas for assistance with the X-ray characterization at IMSERC at Northwestern University, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205); the State of Illinois and International Institute for Nanotechnology (IIN). This work made use of the EPIC facility of Northwestern University’s NUANCE Center (SEM), which has received support from the Soft and Hybrid Nanotechnology Experimental Resource (NSF ECCS-1542205); the MRSEC program (NSF DMR-1720139) at the Materials Research Center; the International Institute for Nanotechnology; the Keck Foundation; and the State of Illinois, through the IIN. Y.P. and Z.C. acknowledge the financial support from the National Natural Science Foundation of China (Grant Nos. 51861145305 and 51772215). G.T. would like to acknowledge the financial support from the Natural Science Foundation of China (Grant No. 11804261) and the Fundamental Research Funds for the Central Universities (WUT: 2019IVA068 and 2019IVB049). The work in the Materials Science Division of Argonne National Laboratory (low-temperature heat capacity measurements) was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, under contract No. DE-AC02-06CH11357. R.H. drafted the manuscript. R.H., M.T.A., and G.J.S. designed the experiment. R.H. and M.T.A. conducted the experimental and theoretical work. A.R. and D.Y.C. conducted the low-T heat capacity measurements. Z.C. and Y.P. synthesized and provided the (Na,Eu)–PbTe sample for characterization. G.T. and M.K. synthesized and provided the (Na,Sr)–PbTe sample for characterization. All authors revised and commented on the manuscript. R.H. acknowledges support from the Johannes and Julia Randall Weertman Graduate Fellowship. M.T.A. acknowledges support from the PPB Graduate Fellowship. G.J.S. and M.T.A. acknowledge thermoelectrics research at Northwestern University through the Center for Hierarchical Materials Design (CHiMaD). R.H. would like to thank Christos Malliakas for assistance with the X-ray characterization at IMSERC at Northwestern University, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205); the State of Illinois and International Institute for Nanotechnology (IIN). This work made use of the EPIC facility of Northwestern University's NUANCE Center (SEM), which has received support from the Soft and Hybrid Nanotechnology Experimental Resource (NSF ECCS-1542205); the MRSEC program (NSF DMR-1720139) at the Materials Research Center; the International Institute for Nanotechnology; the Keck Foundation; and the State of Illinois, through the IIN. Y.P. and Z.C. acknowledge the financial support from the National Natural Science Foundation of China (Grant Nos. 51861145305 and 51772215). G.T. would like to acknowledge the financial support from the Natural Science Foundation of China (Grant No. 11804261) and the Fundamental Research Funds for the Central Universities (WUT: 2019IVA068 and 2019IVB049). The work in the Materials Science Division of Argonne National Laboratory (low-temperature heat capacity measurements) was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, under contract No. DE-AC02-06CH11357. R.H. drafted the manuscript. R.H., M.T.A., and G.J.S. designed the experiment. R.H. and M.T.A. conducted the experimental and theoretical work. A.R. and D.Y.C. conducted the low-T heat capacity measurements. Z.C. and Y.P. synthesized and provided the (Na,Eu)?PbTe sample for characterization. G.T. and M.K. synthesized and provided the (Na,Sr)?PbTe sample for characterization. All authors revised and commented on the manuscript.
Keywords
- lattice dynamics
- thermal conductivity
- thermoelectrics
ASJC Scopus subject areas
- General Materials Science
- Mechanics of Materials
- Mechanical Engineering