Ultralow thermal conductivity and high thermoelectric figure of merit in SnSe crystals

Abstract

The thermoelectric effect enables direct and reversible conversion between thermal and electrical energy, and provides a viable route for power generation from waste heat. The efficiency of thermoelectric materials is dictated by the dimensionless figure of merit, ZT (where Z is the figure of merit and T is absolute temperature), which governs the Carnot efficiency for heat conversion. Enhancements above the generally high threshold value of 2.5 have important implications for commercial deployment1,2, especially for compounds free of Pb and Te. Here we report an unprecedented ZT of 2.6 ± 0.3 at 923 K, realized in SnSe single crystals measured along the b axis of the room-temperature orthorhombic unit cell. This material also shows a high ZT of 2.3 ± 0.3 along the c axis but a significantly reduced ZT of 0.8 ± 0.2 along the a axis. We attribute the remarkably high ZT along the b axis to the intrinsically ultralow lattice thermal conductivity in SnSe. The layered structure of SnSe derives from a distorted rock-salt structure, and features anomalously high Grüneisen parameters, which reflect the anharmonic and anisotropic bonding. We attribute the exceptionally low lattice thermal conductivity (0.23 ± 0.03 W m−1 K−1 at 973 K) in SnSe to the anharmonicity. These findings highlight alternative strategies to nanostructuring for achieving high thermoelectric performance.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

Figure 1: SnSe crystal structure Pnma and ZT values.
Figure 2: Thermoelectric properties as a function of temperature for SnSe crystals.
Figure 3: High-temperature in situ TEM observations.
Figure 4: Theoretically calculated phonon and Grüneisen dispersions, and measured lattice thermal conductivity.

References

  1. 1

    Heremans, J. P., Dresselhaus, M. S., Bell, L. E. & Morelli, D. T. When thermoelectrics reached the nanoscale. Nature Nanotechnol. 8, 471–473 (2013)

    ADS  CAS  Article  Google Scholar 

  2. 2

    Zhao, L. D., Dravid, V. P. & Kanatzidis, M. G. The panoscopic approach to high performance thermoelectrics. Energ. Environ. Sci. 7, 251–268 (2014)

    CAS  Article  Google Scholar 

  3. 3

    Snyder, G. J. & Toberer, E. S. Complex thermoelectric materials. Nature Mater. 7, 105–114 (2008)

    ADS  CAS  Article  Google Scholar 

  4. 4

    Dresselhaus, M. S. et al. New directions for low-dimensional thermoelectric materials. Adv. Mater. 19, 1043–1053 (2007)

    CAS  Article  Google Scholar 

  5. 5

    Heremans, J. P. et al. Enhancement of thermoelectric efficiency in PbTe by distortion of the electronic density of states. Science 321, 554–557 (2008)

    ADS  CAS  Article  Google Scholar 

  6. 6

    Pei, Y. et al. Convergence of electronic bands for high performance bulk thermoelectrics. Nature 473, 66–69 (2011)

    ADS  CAS  Article  Google Scholar 

  7. 7

    Liu, W. et al. Convergence of conduction bands as a means of enhancing thermoelectric performance of n-type Mg2Si1-xSnx solid solutions. Phys. Rev. Lett. 108, 166601 (2012)

    ADS  Article  Google Scholar 

  8. 8

    Hicks, L. D. & Dresselhaus, M. S. Effect of quantum-well structures on the thermoelectric figure of merit. Phys. Rev. B 47, 12727–12731 (1993)

    ADS  CAS  Article  Google Scholar 

  9. 9

    Heremans, J. P., Thrush, C. M. & Morelli, D. T. Thermopower enhancement in lead telluride nanostructures. Phys. Rev. B 70, 115334 (2004)

    ADS  Article  Google Scholar 

  10. 10

    Hsu, K. F. et al. Cubic AgPbmSbTe2+m: bulk thermoelectric materials with high figure of merit. Science 303, 818–821 (2004)

    ADS  CAS  Article  Google Scholar 

  11. 11

    Biswas, K. et al. High-performance bulk thermoelectrics with all-scale hierarchical architectures. Nature 489, 414–418 (2012)

    ADS  CAS  Article  Google Scholar 

  12. 12

    Biswas, K. et al. Strained endotaxial nanostructures with high thermoelectric figure of merit. Nature Chem. 3, 160–166 (2011)

    ADS  CAS  Article  Google Scholar 

  13. 13

    Zhao, L. D. et al. High thermoelectric performance via hierarchical compositionally alloyed nanostructures. J. Am. Chem. Soc. 135, 7364–7370 (2013)

    CAS  Article  Google Scholar 

  14. 14

    Zhao, L. D. et al. Raising the thermoelectric performance of p-type PbS with endotaxial nanostructuring and valence-band offset engineering using CdS and ZnS. J. Am. Chem. Soc. 134, 16327–16336 (2012)

    CAS  Article  Google Scholar 

  15. 15

    Brown, S. R., Kauzlarich, S. M., Gascoin, F. & Snyder, G. J. Yb14MnSb11: new high efficiency thermoelectric material for power generation. Chem. Mater. 18, 1873–1877 (2006)

    CAS  Article  Google Scholar 

  16. 16

    Kurosaki, K., Kosuga, A., Muta, H., Uno, M. & Yamanaka, S. Ag9TITe5: a high-performance thermoelectric bulk material with extremely low thermal conductivity. Appl. Phys. Lett. 87, 061919 (2005)

    ADS  Article  Google Scholar 

  17. 17

    Rhyee, J.-S. et al. Peierls distortion as a route to high thermoelectric performance in In4Se3-δ crystals. Nature 459, 965–968 (2009)

    ADS  CAS  Article  Google Scholar 

  18. 18

    Yu, J. G., Yue, A. S. & Stafsudd, O. M. Growth and electronic properties of the SnSe semiconductor. J. Cryst. Growth 54, 248–252 (1981)

    ADS  CAS  Article  Google Scholar 

  19. 19

    Wasscher, J. D., Albers, W. & Haas, C. Simple evaluation of the maximum thermoelectric figure of merit, with application to mixed crystals SnS1-xSex . Solid-State Electron. 6, 261–264 (1963)

    ADS  CAS  Article  Google Scholar 

  20. 20

    Peters, M. J. & McNeil, L. E. High-pressure Mossbauer study of SnSe. Phys. Rev. B 41, 5893–5897 (1990)

    ADS  CAS  Article  Google Scholar 

  21. 21

    Chattopadhyay, T., Pannetier, J. & Vonschnering, H. G. Neutron-diffraction study of the structural phase-transition in SnS and SnSe. J. Phys. Chem. Solids 47, 879–885 (1986)

    ADS  CAS  Article  Google Scholar 

  22. 22

    Baumgardner, W. J., Choi, J. J., Lim, Y.-F. & Hanrath, T. SnSe nanocrystals: synthesis, structure, optical properties, and surface chemistry. J. Am. Chem. Soc. 132, 9519–9521 (2010)

    CAS  Article  Google Scholar 

  23. 23

    Morelli, D. T., Jovovic, V. & Heremans, J. P. Intrinsically minimal thermal conductivity in cubic I-V-VI2 semiconductors. Phys. Rev. Lett. 101, 035901 (2008)

    ADS  CAS  Article  Google Scholar 

  24. 24

    Fultz, B. & Howe, J. M. Transmission Electron Microscopy and Diffractometry of Materials (Springer, 2012)

    Google Scholar 

  25. 25

    Nielsen, M. D., Ozolins, V. & Heremans, J. P. Lone pair electrons minimize lattice thermal conductivity. Energ. Environ. Sci. 6, 570–578 (2013)

    CAS  Article  Google Scholar 

  26. 26

    Zhang, Y. S. et al. First-principles description of anomalously low lattice thermal conductivity in thermoelectric Cu-Sb-Se ternary semiconductors. Phys. Rev. B 85, 054306 (2012)

    ADS  Article  Google Scholar 

  27. 27

    Slack, G. A. in Solid State Physics (ed. Seitz, F. et al.) 1–71 (Academic, 1979)

    Google Scholar 

  28. 28

    Clarke, D. T. Materials selection guidelines for low thermal conductivity thermal barrier coatings. Surf. Coat. Technol. 163–164, 67–74 (2003)

    Article  Google Scholar 

  29. 29

    Cahill, D. G., Watson, S. K. & Pohl, R. O. Lower limit to the thermal conductivity of disordered crystals. Phys. Rev. B 46, 6131–6140 (1992)

    ADS  CAS  Article  Google Scholar 

  30. 30

    Kresse, G. & Joubert, D. From ultrasoft pseudopotentials to the projector augmented-wave method. Phys. Rev. B 59, 1758–1775 (1999)

    ADS  CAS  Article  Google Scholar 

  31. 31

    Perdew, J. P., Burke, K. & Ernzerhof, M. Generalized gradient approximation made simple. Phys. Rev. Lett. 77, 3865–3868 (1996)

    ADS  CAS  Article  Google Scholar 

  32. 32

    Monkhorst, H. J. & Pack, J. D. Special points for Brillouin-Zone integrations. Phys. Rev. B 13, 5188–5192 (1976)

    ADS  MathSciNet  Article  Google Scholar 

  33. 33

    van de Walle, A., Asta, M. & Ceder, G. The alloy theoretical automated toolkit: a user guide. Calphad 26, 539–553 (2002)

    CAS  Article  Google Scholar 

  34. 34

    Cahill, D. G., Watson, S. K. & Pohl, R. O. Lower limit to the thermal conductivity of disordered crystals. Phys. Rev. B 46, 6131–6140 (1992)

    ADS  CAS  Article  Google Scholar 

  35. 35

    Chattopadhyay, T., Pannetier, J. & Vonschnering, H. G. Neutron-diffraction study of the structural phase-transition in SnS and SnSe. J. Phys. Chem. Solids 47, 879–885 (1986)

    ADS  CAS  Article  Google Scholar 

  36. 36

    Baumgardner, W. J., Choi, J. J., Lim, Y.-F. & Hanrath, T. SnSe nanocrystals: synthesis, structure, optical properties, and surface chemistry. J. Am. Chem. Soc. 132, 9519–9521 (2010)

    CAS  Article  Google Scholar 

Download references

Acknowledgements

This work was supported in part by Revolutionary Materials for Solid State Energy Conversion, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, and Office of Basic Energy Sciences under award number DE-SC0001054 (L.-D.Z., S.-H.L., Y.Z., H.S., G.T., C.U., C.W., V.P.D. and M.G.K.). TEM work was performed in the (EPIC, NIFTI, Keck-II) facility of the NUANCE Center at Northwestern University. The NUANCE Center is supported by NSF-NSEC, NSF-MRSEC, the Keck Foundation, the State of Illinois and Northwestern University.

Author information

Affiliations

Authors

Contributions

L.-D.Z. synthesized the samples, designed and carried out thermoelectric experiments, and wrote the paper. S.-H.L. and V.P.D. performed the TEM characterizations. Y.Z. carried out the calculations. H.S. and C.U. carried out the Hall measurements. G.T. helped with sample synthesis. L.-D.Z., S.-H.L., Y.Z., H.S., G.T., C.U., C.W., V.P.D. and M.G.K. conceived the experiments, analysed the results and co-edited the manuscript. S.-H.L. and Y.Z. contributed equally.

Corresponding author

Correspondence to Mercouri G. Kanatzidis.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Extended data figures and tables

Extended Data Figure 1 XRD measurement of SnSe on the cleavage plane, and the simulated diffraction pattern.

The (400) reflection plane indicates that the SnSe crystal is cleaved at the plane that is perpendicular to the a axis. Source data

Extended Data Figure 2 EBSD analysis on a 1 mm2 surface.

a, The all-Euler map showing a large area of sample surface with homogeneous orientation. b, The inverse pole figures of samples cut along the ab, ca and bc planes, respectively. The view down the c-axis (left figure) indicates a slight deviation (11°) from it. Scale bar, 200 μm.

Extended Data Figure 3 Hall transport properties of crystalline SnSe.

a, Inverse RH (RH, Hall coefficient), and b, RH/ρ (ρ, electrical resistivity) of SnSe crystals along different axial directions. Inverse RH gives an indication of the carrier concentration; RH/ρ is related to the carrier mobility. Source data

Extended Data Figure 4 Electronic band structures of low-temperature (Pnma) and high-temperature (Cmcm) phases of SnSe.

a, SnSe at low temperature (Low-T) with the Pnma space group. b, SnSe at high temperature (High-T) with the Cmcm space group. The dashed lines indicate the position of the Fermi level (EF). Inset figures are the first Brillouin zones (BZ) of SnSe with high-symmetry points (red points) that we considered in our band structure calculations. Both phases are indirect-bandgap (Eg) compounds. For the low-temperature phase, the indirect bandgap is along ΓY in its BZ; for the high-temperature phase, the indirect bandgap is from a point within the ΓP direction to the Z point in its BZ.

Extended Data Figure 5 Bandgap of SnSe at room temperature.

Optical absorption spectrum (black trace) and energy bandgap (x-axis intercept) indicate a bandgap of 0.86 eV (red) of SnSe at room temperature. See Methods for details of α and S. Source data

Extended Data Figure 6 Thermoelectric properties as a function of temperature for crystalline SnSe along different directions.

a, Thermal diffusivity. b, Heat capacity. c, Electronic thermal conductivity. d, The ratio of lattice thermal conductivity (κlat) to total thermal conductivity (κtot). The Lorenz number (L) used for obtaining κlat (κlat = κtot − σLT, where σ is the electrical conductivity and T is absolute temperature) was approximately equal to 1.5 × 10−8 V2 K−2 since the undoped SnSe is a non-degenerate semiconductor; the ratio of κlat to κtot indicates that κtot is dominated by phonon transport. Source data

Extended Data Figure 7 High-resolution TEM images of single-crystal SnSe along four zone axes, and SAD along a low-order zone axis (in insets).

a, Along the [100] direction. b, Along the [201] direction. c, Along the [211] direction. d, Along the [021] direction. e, Electron diffraction pattern along the [001] direction. f, Electron diffraction pattern along the [010] direction. The combination of all six figures provides strong evidence of the single-crystal orthorhombic layered structure of SnSe.

Extended Data Figure 8 Simulated SADs for SnSe.

a, Room-temperature (RT; Pnma) phase; b, high-temperature (HT; Cmcm) phase. B, zone axis. Note is used here to indicate −1.

Extended Data Figure 9 Differential thermal analysis of SnSe.

DTA measurements showing two heating and cooling cycles. DTA results indicate that SnSe appears to melt congruently; one endothermic peak is observed at 881 °C on the heating curve and one exothermic peak is observed at 868 °C on the cooling curve. Two heating–cooling cycles indicate the same melting and crystallization point for a given sample, consistent with high purity. Heat flow is represented as a μV signal, plotted on the y axis. Source data

Extended Data Figure 10 Reproducibility, and thermoelectric properties as a function of temperature, for seven samples of SnSe crystals along the b axis.

a, Electrical conductivity. b, Seebeck coefficient. c, Power factor. d, Total thermal conductivity. e, ZT; error bars are ±15%. Source data

Extended Data Table 1 Transverse (TA/TA’) and longitudinal (LA) Debye temperatures (Θ), phonon velocities (v) and Grüneisen parameters (γ) along a, b and c axes in the low-temperature SnSe phase.

PowerPoint slides

Source data

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Zhao, L., Lo, S., Zhang, Y. et al. Ultralow thermal conductivity and high thermoelectric figure of merit in SnSe crystals. Nature 508, 373–377 (2014). https://doi.org/10.1038/nature13184

Download citation

Further reading

Comments

By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.

Search

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing