Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Article
  • Published:

Giant thermoelectric Seebeck coefficient of a two-dimensional electron gas in SrTiO3

Abstract

Enhancement of the Seebeck coefficient (S ) without reducing the electrical conductivity (σ) is essential to realize practical thermoelectric materials exhibiting a dimensionless figure of merit (Z T=S2·σ·T·κ−1) exceeding 2, where T is the absolute temperature and κ is the thermal conductivity. Here, we demonstrate that a high-density two-dimensional electron gas (2DEG) confined within a unit cell layer thickness in SrTiO3 yields unusually large |S|, approximately five times larger than that of SrTiO3 bulks, while maintaining a high σ2DEG. In the best case, we observe |S|=850 μV K−1 and σ2DEG=1.4×103 S cm−1. In addition, by using the κ of bulk single-crystal SrTiO3 at room temperature, we estimate ZT2.4 for the 2DEG, corresponding to ZT0.24 for a complete device having the 2DEG as the active region. The present approach using a 2DEG provides a new route to realize practical thermoelectric materials without the use of toxic heavy elements.

This is a preview of subscription content, access via your institution

Access options

Rent or buy this article

Prices vary by article type

from$1.95

to$39.95

Prices may be subject to local taxes which are calculated during checkout

Figure 1: Structure and TE response of the 2DEG confined in an MQW composed of SrTiO3 (barrier)/SrTi0.8Nb0.2O3 (well)/SrTiO3 (barrier).
Figure 2: 2DEG localized at the TiO2/SrTiO3 heterointerface.
Figure 3: Giant Seebeck coefficient |S| originating from the 2DEG localized in a unit cell layer of SrTiO3.
Figure 4: TE figures of merit, Z T, of the 2DEGs and the SrTiO3-bulk samples as a function of carrier concentration at room temperature.

Similar content being viewed by others

References

  1. Tritt, T. M. et al. Thermoelectric materials, phenomena, and applications: A bird’s eye view. Mater. Res. Soc. Bull. 31, 188–198 (2006).

    Article  Google Scholar 

  2. DiSalvo, F. J. Thermoelectric cooling and power generation. Science 285, 703–706 (1999).

    Article  CAS  Google Scholar 

  3. Sales, B. C. & Mandrus, D. Filled skutterudite antimonides: a new class of thermoelectric materials. Science 272, 1325–1328 (1996).

    Article  CAS  Google Scholar 

  4. Poon, S. J. Electronic and thermoelectric properties of half-Heusler alloys. Semicond. Semimet. 70, 37–75 (2001).

    Article  CAS  Google Scholar 

  5. Nolas, G. S., Cohn, J. L., Slack, G. A. & Schujman, S. B. Semiconducting Ge clathlates: Promising candidate for thermoelectric applications. Appl. Phys. Lett. 73, 178–180 (1998).

    Article  CAS  Google Scholar 

  6. Snyder, G. J., Christensen, M., Nishibori, E., Caillat, T. & Iversen, B. Disordered zinc in Zn4Sb3 with phonon-glass and electron-crystal thermoelectric properties. Nature Mater. 3, 458–463 (2004).

    Article  CAS  Google Scholar 

  7. Venkatasubramanian, R., Siivola, E., Colpitts, T. & O’Quinn, B. Thin-film thermoelectric devices with high room-temperature figures of merit. Nature 413, 597–602 (2001).

    Article  CAS  Google Scholar 

  8. Harman, T. C., Taylor, P. J., Walsh, M. P. & LaForge, B. E. Quantum dot superlattice thermoelectric materials and devices. Science 297, 2229–2232 (2002).

    Article  CAS  Google Scholar 

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

    Article  CAS  Google Scholar 

  10. Terasaki, I., Sasago, Y. & Uchinokura, K. Large thermoelectric power in NaCo2O4 single crystals. Phys. Rev. B 56, R12685–R12687 (1997).

    Article  CAS  Google Scholar 

  11. Shikano, M. & Funahashi, R. Electrical and thermal properties of single-crystalline (Ca2CoO3)0.7CoO2 with a Ca3Co4O9 structure. Appl. Phys. Lett. 82, 1851–1853 (2003).

    Article  CAS  Google Scholar 

  12. Okuda, T., Nakanishi, K., Miyasaka, S. & Tokura, Y. Large thermoelectric response of metallic perovskites: Sr1−xLaxTiO3 (0≤x≤0.1). Phys. Rev. B 63, 113104 (2001).

    Article  Google Scholar 

  13. Ohta, S., Nomura, T., Ohta, H. & Koumoto, K. High-temperature carrier transport and thermoelectric properties of heavily-electron doped SrTiO3 single crystals. J. Appl. Phys. 97, 034106 (2005).

    Article  Google Scholar 

  14. Ohta, S. et al. Large thermoelectric performance of heavily Nb-doped SrTiO3 epitaxial film at high temperature. Appl. Phys. Lett. 87, 092108 (2005).

    Article  Google Scholar 

  15. Touloukian, Y. S., Powell, R. W., Ho, C. Y. & Klemens, P. G. Thermophysical Properties of Matter Volume 2, Thermal Conductivity: Nonmetallic Solids (IFI/Plenum, New York-Washington, 1970).

    Google Scholar 

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

    Article  CAS  Google Scholar 

  17. Hicks, L. D., Harman, T. C., Sun, X. & Dresselhaus, M. S. Experimental study of the effect of quantum-well structures on the thermoelectric figure of merit. Phys. Rev. B 53, R10493–R10496 (1996).

    Article  CAS  Google Scholar 

  18. Buban, J. P. et al. Grain boundary strengthening in alumina by rare earth impurities. Science 311, 212–215 (2006).

    Article  CAS  Google Scholar 

  19. Ohtomo, A., Muller, D. A., Grazul, J. L. & Hwang, H. Y. Artificial charge-modulation in atomic-scale perovskite titanate superlattices. Nature 419, 378–380 (2002).

    Article  CAS  Google Scholar 

  20. Frederikse, H. P. R., Thurber, W. R. & Hosler, W. R. Electronic transport in strontium titanate. Phys. Rev. A 134, 442–445 (1964).

    Article  CAS  Google Scholar 

  21. Cowley, R. A. Lattice dynamics and phase transitions of strontium titanate. Phys. Rev. A 134, 981–997 (1964).

    Article  CAS  Google Scholar 

  22. Nilsen, W. G. & Skinner, J. G. Raman spectrum of strontium titanate. J. Chem. Phys. 48, 2240–2248 (1968).

    Article  CAS  Google Scholar 

  23. Cantrell, D. G. & Butcher, P. N. A calculation of the phonon-drag contribution to the thermopower of quasi-2D electrons coupled to 3D phonons: I. General theory. J. Phys. C: Solid State Phys. 20, 1985–1992 (1987).

    Article  Google Scholar 

  24. Jonker, G. H. Application of combined conductivity and Seebeck-effect plots for analysis of semiconductor properties. Phil. Res. Rep. 23, 131–138 (1968).

    Google Scholar 

Download references

Acknowledgements

This work was financially supported by the Industrial Technology Research Grant Program in 2005 from the New Energy and Industrial Technology Development Organization (NEDO) and a Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology (No. 18686054).

Author information

Authors and Affiliations

Authors

Corresponding author

Correspondence to Hiromichi Ohta.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Rights and permissions

Reprints and permissions

About this article

Cite this article

Ohta, H., Kim, S., Mune, Y. et al. Giant thermoelectric Seebeck coefficient of a two-dimensional electron gas in SrTiO3. Nature Mater 6, 129–134 (2007). https://doi.org/10.1038/nmat1821

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/nmat1821

This article is cited by

Search

Quick links

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