Materials for Thermoelectric Applications

Materials for Thermoelectric Applications

Jorge O. SofoDepartment of Physics,

Department of Materials Science and Engineering,and

Materials Research InstitutePenn State

Thermoelectricians at work

2SZ

Thermoelectricians at work

Conductivity 101

mne2Drude et al.

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coll

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f fdkdt tk

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SZ

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2 2

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k B Bk

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v

Transport distribution

[ ] [ ]S

[ ]el

max [ ] [ ]best bestZ Z

)()( 0 Cbest TkB4.20

2

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SZ Z

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B

fkS dk T

2

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k T

“The best thermoelectric,” G. D. Mahan and J. O. SofoProc. Nat. Acad. Sci. USA, 93, 7436 (1996)

The “Best” Thermoelectric

)()( kkk

kk vv

)()()( 2 vN

)()( 0 Cbest TkB4.20

k

dSN

1)(

kv )(

Exciting Conductivity

kkkk

vvfe�

0

2kv

kk

1

kpm1

kpkm

ˆ1

k First Born Approximation• Acoustic phonons• Optical phonons (polar,

non-polar)• Ionized impurities• Inter-valley scattering• …

C. Ambrosch-Draxl and J. O. SofoLinear optical properties of solids within the full-potential linearized augmented planewave methodComp. Phys. Commun. 175, 1-14 (2006)

Careful…

• Doping: rigid band• Gap problem• Temperature dependence of the electronic

structure.• Alloys. Single site approximations do not work.• Many k-points

T. J. Scheidemantel, C. Ambrosch-Draxl, T. Thonhauser, J. V. Badding, and J. O. Sofo. “Transport Coefficients from First-principles Calculations.” Phys. Rev. B 68, 125210 (2003)

Bi2Te3

Bismuth

Why is Bi so good?

Bi vs. Bi2Te3

Improved thermoelectric devices using bismuth alloysT. Thonhauser, T. J. Scheidemantel, J. O. Sofo, Appl. Phys. Lett. 85, 588 (2004)

Is there any hope?

Courtesy of Georg Madsen

A Program by Georg Madsen and David Singh

Courtesy of Georg Madsen

Georg Madsen’s

Opals

• Different scattering for phonons and electrons.

• Work done for Allied Signal Corp.

• Not an alternative…

•

Summary

• Tool to explore new compounds, pressure, “negative” pressure.

• Prediction of a new compound by G. Madsen.• Easy to expand adding new Scattering

Mechanisms• Limited to applications on “non-correlated”

semiconductors.• The search for the best material continues…