Nanopowder thermoelectrics: improved energy conversion by - - PowerPoint PPT Presentation

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Nanopowder thermoelectrics: improved energy conversion by nanostructuring Sabine Schlecht DFG-JST Workshop Kyoto, 20.- 23. January 2009 Thermoelectric effects interconversion of thermal and electrical energy Seebeck 1821: difference in

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Nanopowder thermoelectrics: improved energy conversion by nanostructuring

Sabine Schlecht DFG-JST Workshop Kyoto, 20.- 23. January 2009

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Thermoelectric effects

interconversion of thermal and electrical energy

+ -

Peltier 1834: difference in temperature from a difference in potential (cooling) Seebeck 1821: difference in potential from a difference in temperature (TE generator)

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Fields of application for TE converters

Peltier element RTG-New Horizons TEG for vehicles Woodstove with TEG TEG for sensing

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Nanoscale Thermoelectrics

Efficiency of TE conversion (Altenkirch 1909): figure of merit ZT= (S2·σ)/κ

Why nano ?

  • reduction of κ
  • Influence on S and σ ?
  • concept of ‚electron

crystal‘ and ‚phonon glass‘

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S for nanoscale PbSe films

bulk PbSe nano PbSe

Changes of TE parameters on the nanoscale

Insulator Semiconductor Semimetal Metal

charge carrier concentration

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Effects of nanostructuring on ZT

multi quantum well structure

  • rdered super lattice

in-plane transport cross-plane transport electrical conductivity thermal conductivity

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Super lattices of layers and quantum dots

pioneered by Harman, Venkatasubramanian

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Reduction of the thermal conductivity by phonon scattering

  • R. Yang, G. Chen, M. S. Dresselhaus
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Types of nanocomposite powders

A C B

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SEM image TEM image

TE data for nano-Bi0.5Sb1.5Te3

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TE data for nano-Bi0.5Sb1.5Te3

σ (nano) slightly higher than σ (bulk) κ (nano) significantly lower than κ (bulk)

  • effective phonon scattering at a large number
  • f grain boundaries
  • doping level and structural defects

Improvement of the figure of merit ZT (nano) (200°C) = 1.1 ZT (bulk) (200°C) = 0.4

  • B. Poudel, Q. Hao, Y. Lan, A. Minnich, Z. Ren, Science, 2008, 305, 638.
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  • averaged rock salt structure
  • Ag- und Sb-rich nanoscopic

inclusions

  • very effective phonon scattering
  • ZT values up to 2.2
  • M. G. Kanatzidis, Michigan State

Nanoscopic de-mixing: formation of a nanocomposite (LAST materials)

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Syntheses from activated elements

Tellurides Pb* + Ph2Te2 nc-PbTe + Ph2Te Antimonides (solid-solid reactions) 4 Zn* + 3 Sb* nc-Zn 4Sb3 Zn* + Sb* nc-ZnSb Co* + 3 Sb* nc-CoSb3

165°C diglyme

300°C/275°C 300°C 300°C

165°C diglyme

2 Sb* + 3 Ph2Te2 nc-Sb2Te3 + 3 Ph2Te

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ZnSb nanopowders (13 nm)

20 nm 2 nm

[021]

particle size ~ 13 nm

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Compacting and TE data for nc-ZnSb

  • Uniaxial hot-pressing (450°C, 100 MPa):

stable samples with a density of 4.9 g/cm3

  • Seebeck coefficient S = 253 ± 2 μV/K

(bulk: 196 μV/K)[1]

50 100 150 200 250 300 350 400 50 100 150 200 250 300 y0 xc 253.13 ±1.07 w 80.54 ±2.14 R^2 = 0.9797

Times measured Seebeck coefficient [µV/K]

S2σ = 6.8 μW/(K2 cm) nc-ZnSb S2σ = 3.5 μW/(K2 cm) bulk-ZnSb[1]

50 100 150 200 250 300 350 400 50 100 150 200 250 300 bulk-ZnSb nc-ZnSb

T (°C) σ (Ω-1 cm-1)

[1] P. J. Shaver, J. Blair, Phys. Rev. 1966, 141, 649.

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50 100 150 200 250 300 2,0 2,1 2,2 2,3 2,4 2,5 2,6

nc-ZnSb

κ [W/(m·K)] T (°C) ZT (293 K) = 0.100 nc-ZnSb ZT (293 K) = 0.044 bulk-ZnSb ZT (nano) = 2.2 ZT (bulk)

[2] L. T. Zhang, M. Tsutsui, J. All. Comp. 2003, 358, 252. [1] P. J. Shaver, J. Blair, Phys. Rev. 1966, 141, 649.

Compacting and TE data for nc-ZnSb

  • Uniaxial hot-pressing (450°C, 100 MPa):

stable samples with a density of 4.9 g/cm3

  • Seebeck coefficient S = 253 ± 2 μV/K

(bulk: 196 μV/K)[1]

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25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 200 400 600 800 1000

y0 15.71279 ± 3.90351 xc 58.157 ± 0.03923 w 3.71869 ± 0.09006 A 2162.82692 ± 55.23262

Count Seebeck coefficient [µV/K]

50 100 150 200 250 300 350 40 60 80 100 120 140

T [°C]

ZnSb SPS ZnSb HUP

density 4.7 g/cm3

Influence of the method of compacting: ZnSb (20 nm)

S(T) for HUP and SPS S-scan after one thermal cycle

Improved stability of data with prolonged synthetic procedure

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x nc-PbTe + nc-Sb2Te3 PbxSb2Tex+3

400°C, 17 h quenched

(x = 20,10)

Ternary Phases in the System PbTe - Sb2Te3

enlarged [200] reflections

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Summary and Outlook

Thermoelectric energy conversion shows excellent potential for future recovery of waste heat in industry, vehicles and household current and further miniturizarion allow the use of TE converters for sensing, communication, integrated systems and in biomedical industries nanostructuring of good TE semiconductors has already shown the potential for a ZT of 2 that is required for widespread application the need for more efficient energy recycling will also lead to relevant discoveries in the field of fundamental research (natural sciences and engineering)

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Acknowledgement

Coworkers

  • D. Petri
  • I. B. Angelov
  • M. Artamonowa
  • C. Erk
  • M. Roskamp
  • W. Meng
  • B. N. Ghosh
  • C. Rohner

Cooperations

  • Dr. M. Steinhart (MPI Halle)
  • Prof. Dr. B. Koksch (FU Berlin)
  • Prof. Dr. H.-U. Reißig (FU Berlin)
  • Dr. J. Dernedde (Charité, Berlin)
  • Dr. H. Böttner, Dr. D. Ebling (Fraunhofer

IPM, Freiburg)

  • Dr. E. Müller, C. Stiewe (DLR Köln)

Funding Deutsche Forschungsgemeinschaft (SFB 765, SPP 1165, SPP 1386) Fonds der Chemischen Industrie (to C.E.)

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