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  • WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MITWARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT

    Nanostructured Thermoelectric Materials: From Basic Physics to Applications

    Gang Chen

    Nanoengineering GroupRohsenow Heat and Mass Transfer Laboratory

    Massachusetts Institute of Technology

    Cambridge, MA 02139

    Email: gchen2@mit.eduhttp://web.mit.edu/nanoengineering

    Acknowledgments:J.P. Fleurial

    DOE, NSF, and Industry

  • WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MITWARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT

    Outline

    Why nanocomposites?

    What we have achieved?

    What we do not understood?

    Application opportunities

  • WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MITWARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT

    Nanoscale Effects for Thermoelectrics

    Phonons=10-100 nm

    =1 nm

    Electrons=10-100 nm=10-50 nm

    Electron Phonon

    Interfaces that Scatter Phonons but not Electrons

  • WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MITWARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT

    0

    20

    40

    60

    80

    10 1 10 2 10 3 10 4

    THER

    MA

    L C

    ON

    DU

    CTI

    VITY

    (W/m

    K)

    LAYER THICKNESS ()

    BULK

    SPECULAR (p=1)

    p=0.95

    p=0.8DIFFUSE (p=0)

    Yao (1987)Yu et al. (1995)0

    20

    40

    60

    80

    10 1 10 2 10 3 10 40

    20

    40

    60

    80

    0

    20

    40

    60

    80

    10 1 10 2 10 3 10 410 1 10 2 10 3 10 4

    THER

    MA

    L C

    ON

    DU

    CTI

    VITY

    (W/m

    K)

    LAYER THICKNESS ()

    BULK

    SPECULAR (p=1)

    p=0.95

    p=0.8DIFFUSE (p=0)

    Yao (1987)Yu et al. (1995)

    Heat Conduction Mechanisms in Superlattices

    Periodic Structures Are Not Necessary, Nor Optimal!

    Major Conclusions:

    Ideal superlattices do not cut off all phonons due to pass-bands

    Individual interface reflection is more effective

    Diffuse phonon interface scattering is crucial

    10-1

    100

    101 102 103Capinski et al. 1999Capinski et al. 1999

    Yao 1987 Yu et al. 1995

    Nor

    mal

    ized

    The

    rmal

    Con

    duct

    ivity

    Period Thickness ()

    T=300KAlAs/GaAs

    In-Plane

    Cross-Plane

    LD

    LD

    Ideal Superlattices

    In-Plane

    Cros

    s-Pl

    ane

  • WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MITWARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT

    Nanocomposites Approach

    Increase interfacial scattering by mixing nano-sized particles.

    Enable batch fabrication for large scale application.

    Nanoparticle(a) (b)

  • WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MITWARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT

    Low-Cost Synthesis

    AGraphite cylinder

    Graphite piston

    Current for heating

    Force for pressing

    Sample powder A

    Graphite cylinder

    Graphite piston

    Current for heating

    Force for pressing

    Sample powder

  • WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MITWARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT

    Thermoelectric Properties: Bi2

    Te3

    Poudel et al., Science, 320, 634, 2008

  • WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MITWARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT

    Six

    Ge1-x

    System

    Joshi et al., Nano Letters 8, 4670 (2008)

    Wang, et al.

    Appl. Phy. Lett. 93, 193121 (2008)

    P-type SiGe

    N-type SiGe

    0 200 400 600 800 10000.0

    0.2

    0.4

    0.6

    0.8

    1.0

    1.2

    1.4 RTG SiGe Si80Ge20B5 (run-1) Si80Ge20B5(run-1)- annealed 7 days Si80Ge20B5(run-2)

    ZT

    Temperature ( oC)

    0

    5

    10

    15

    20

    25

    30

    35

    40

    45

    200 400 600 800 1000 1200 1400

    Ther

    mal

    Con

    duct

    ivity

    (W.m

    -1K-

    1 )

    Temperature (K)

    No large cold welded agglomeratesShort Pressure Sintering at 1275 KLong Pressure Sintering at 1475 K

    Undoped SiSingle Crystal

    Doped Nanobulk Si using only "cold

    welded" agglomerates of nanoparticles

    Undoped Nanobulk Si

    Doped Nanobulk Si

    Bux et al., Adv. Func. Mat., 2009

  • WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MITWARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT

    Understanding Electron and Phonon Transport in Random Nanostructures

    5 nm

    Phonons:

    What is the mean free path in bulk materials Phonon-phonon Dopants Alloy Electron scattering Defects

    How phonons are scattered at an interfaces Interface roughness Crystallographic directions Anharmonic effect

  • WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MITWARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT

    Molecular Dynamics Simulation of Phonon Mean Free Path

    10-3

    10-2

    10-1

    100

    101

    102

    103

    0

    10

    20

    30

    40

    50

    60

    70

    80

    90

    100

    Mean Free path (m)

    Per

    cen

    t A

    ccu

    mu

    lati

    on

    CallawayAseMD

    Henry and Chen, J. Comp. Theo. Nanosci., 5, 141 (2008).

    Si

  • WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MITWARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT

    0.0

    0.2

    0.4

    0.6

    0.8

    1.0

    1.2

    0.00

    0.05

    0.10

    0.15

    0.20

    0 30 60 90

    SV

    TO

    SV

    WA

    VE SV

    TO L W

    AV

    E

    INCIDENT ANGLE (DEGREE)

    REFLECTIVITYTRANSMISSIVITY

    REFLECTIVITY

    TRANSMISSIVITY

    Interface Reflectivity and Transmissivity

    L(v)1(v)2

    sv

    L

    svsv

    We know how to do it only in the continuum limit, with perfect interfaces!

  • WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MITWARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT

    Thermal Interface Resistance Between Perfectly Contact Solids

    Cahill et al., JAP, 2003

    No model can predict interface thermal conductance except at very low temperatures.

    Phonon transmissivity and reflectivity at interfaces are crucial parameters to model heat conduction in thermoelectric materials.

  • WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MITWARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT

    Electron Transport

    Where thermoelectric effect happens?

    Interfacial barrier height

    Momentum conservation at interfaces

    Scattering inside particles

    Energy dependency of scattering

    5 nm

  • WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MITWARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT

    Thermionic emission at grain boundaries

    SiGe nanocomposite,

    Eb

    =0.2eV, ND

    =4x1020

    cm-3

    Need: Em

  • WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MITWARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT

    Nanoparticle/Nanograin Scattering

    D/2carrier

    Dominant electron wavelengths

    * ~ 6 10nmc

    hm v

    Grain size

    m~ 20 n30D

    Grain boundary thicknessm~1ntDebye screening length1/2

    2 ~ 0.5 m1 nDkTLe N

    Nanograin

    D/2D/2carrier

    Dominant electron wavelengths

    * ~ 6 10nmc

    hm v

    Grain size

    m~ 20 n30D

    Grain boundary thicknessm~1ntDebye screening length1/2

    2 ~ 0.5 m1 nDkTLe N

    Dominant electron wavelengths

    * ~ 6 10nmc

    hm v

    Grain size

    m~ 20 n30D

    Grain boundary thicknessm~1ntDebye screening length1/2

    2 ~ 0.5 m1 nDkTLe N

    Nanograin

  • WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MITWARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT

    Electrons: MFP vs

    5 10 15 20 25 301

    1.5

    2

    2.5

    3

    3.5

    4

    4.5

    5

    5.5

    6

    MF

    P (

    nm

    )

    Electron wavelength (nm)

    Minnich et al., Energy & Env. Sci., 2009.

    SiGe

  • WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MITWARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT

    Potential Applications

    Industrial Waste Heat (DOE/ITP)

    Renewables

    Transportation

    Main AC: TE Local cooling of seats: TE

    Catalytic converter: TE

    Radiator: TE

    Main AC: TE Local cooling of seats: TE

    Catalytic converter: TE

    Radiator: TE

    BuildingsCombustor: TE

    Solar Panel: PVSolar Panel: PV

    Furnace: TE

    Refrigerator

    HVAC: TE

    And Entropy is Generated

  • WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MITWARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT

    System Consideration

    TobjectTcold

    Thot

    TambientT

    Tte

    Sometimes, thermal systems more expansive

  • WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MITWARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MIT

    Heat to Electricity Recovery from Gas Stream

    Hot Gasm, Th

    ,i

    Hot GasTh

    ,o

    Heat Transfer Surfaces

    Coolant

    InsulationHot Side TemperatureTH

    Cold Side TemperatureTc

    For thermoelectric devices, TH

    higher is better

    However, maximum heat intercepted from hot gas stream, mcp

    (Th,i

    -TH

    ), decreases with TH

  • WARREN M. ROHSENOW HEAT AND MASS TRANSFER LABORATORY, MITWARREN M. ROHSENOW HEAT AND MASS TRANSFER LA

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