Nanostructures Thermoelectrics. The New

paradigm

Sponsored by the

Mercouri Kanatzidis

Department of Energy

2012 Thermoelectric Applications Workshop Baltimore, MD

electronic band structure of PbTe

a≈6.45 Å (300K)

m*Σ (~2m0) >> m*L(~0.2m0)

Valence band is multiple peaks

L Σ

E (e

V)

~0.26 eV

T = 300 K

VB

CB

Light hole band Heavy hole band

EF

L Σ

E (e

V)

~0.30 eV

T = 500 K

VB

CB

Light hole band Heavy hole band

Thermal excitation of holes to Σ band

Valence bands of PbTe….

Rising temperature

10/24/11

Earth abundant materials: Recent exciting results: thermal conductivity reduction

thermal conductivity reduction below alloy limit

PbSe-PbS x%

Density of precipitates increases with increasing x.

PbSe-x%PbS : doped with 0.3% of In x = 0, 4, 8, and 16

• 0% of PbS/0.3% of In : 3.04E19 cm-3 • 4% of PbS/0.3% of In : 3.68E19 cm-3 • 8% of PbS/0.3% of In : 5.58E19 cm-3 • 12% of PbS/0.3% of In : 4.67E19 cm-3 • 8% of PbS/0.3% of Pb* : 2.6E19 cm-3 • 8% of PbS/0.3% of PbCl2* : 2.8E19 cm-3 • 12% of PbS/0.3% of PbCl2* : 2.4E19 cm-3 • 16% of PbS/0.3% of PbCl2* : 2.2E19 cm-3 • 12% of PbS/0.3% of Bi* : 3.2E19 cm-3

Androulakis, J. ; Todorov, I. ; He, J. ; Chung, D. ; Dravid, V. ; Kanatzidis, M. ; J. Am. Chem. Soc. 2011, 133, 10920

10/24/11

PbSe-PbS system: high ZT at 900K

Dopant plays strong role in the resulting ZT.

PbSe-PbS

Thermoelectric Properties of n-type PbS

Binary phase diagram of PbS-Bi2S3(Sb2S3) Garvin P. F., Neues Jahrb. Mineral., Abh., 118, 235(1973)

PbS-Bi2S3 phase diagram

The solubility limit of PbCl2 in PbS ranges between 1.0 and 2.0 mol %

n-type PbS

PbS with second phases without doping

n-type PbS with second phases

Second phases: Bi2S3, Sb2S3

~ 0.80 @ 723 K

300 400 500 600 7000

500

1000

1500

2000

2500

σ(Sc

m-1)

PbS PbS+1% PbCl2 PbS+1% Bi2S3+1% PbCl2 PbS+2% Bi2S3+1% PbCl2 PbS+3% Bi2S3+1% PbCl2 PbS+4% Bi2S3+1% PbCl2 PbS+5% Bi2S3+1% PbCl2

Temperature (K)

300 400 500 600 700-400

-300

-200

-100

0

S(µV

K-1 )

Temperature (K)

Seebeck independent on second phases

300 400 500 600 7000

3

6

9

12

15

PF (µW

cm-1K-

2 )

Temperature (K)

Significantly reduce

300 400 500 600 7000.0

0.2

0.4

0.6

0.8

1.0 PbS PbS+1% PbCl2 PbS+1% Sb2S3+1% PbCl2 PbS+2% Sb2S3+1% PbCl2 PbS+3% Sb2S3+1% PbCl2 PbS+4% Sb2S3+1% PbCl2 PbS+5% Sb2S3+1% PbCl2

Temperature (K)

ZT

PbS with Sb2S3~ 0.78 @ 723 K

n-type PbS with second phases

PbS+1.0 at. % Bi2S3+1.0 at. % PbCl2 PbS + 1.0 at. % Sb2S3 + 1.0 at. % PbCl2

TEM: nanostructured PbS

ZT ~ 1.1 @ 923 K ZT ~ 1.06 @ 923 K

M: normal melting B: Bridgman S: SPS BN coating

Good repeatability !

Nanostructures n-type PbS, ZT=1.1

Atoms/molecular motifs

Crystal lattice & point defects

Interfaces

Macro-, and device-scale Interfaces

Precipitates & nanoscale defects

Electronic Structure

Crystal Structure

Classical Microstructure

Thin films/multilayers Interfaces Residual stresses

Macroscale Device Architecture

Angstrom and sub-nm scale

Sub-nm to Nano-scale

Micro-to macro-scale

Hierarchical Length-scale

Architecture:

Implications for “Nanostructured”

Thermoelectrics

Interactions along varied length-scales

Identification of individual microstructure elements in electronic and phonon transport

Tailoring and design of “microstructure”

Panoscopic view of thermoelectrics

Conclusions

• Strain at interfaces increases phonon scattering • Small nanostructured (1-10 nm) are more likely to create

strain • Superior properties in p-type PbTe-SrTe achieved through

endotaxial placement of nanoprecipitates – Nanostructures do not reduce the power factor and function

exclusively as phonon scatterers

• Large power factor enhancements are need for continued ZT increases

• PbSe-PbS is nanostructured! • PbSe-PbS n-type ZT ~1.3 at 900K. • High performance in PbS (ZT>1)

Nanostructures Thermoelectrics. The New paradigmSlide Number 2CollaboratorsSlide Number 4Slide Number 5Introducing strain into PbTeSlide Number 7Slide Number 8Slide Number 9Slide Number 10Slide Number 11Slide Number 12Slide Number 13Optimizing charge transportSlide Number 15CaTe in PbTeEarth abundant materials: Recent exciting results: thermal conductivity reduction�Slide Number 18PbSe-x%PbS : doped with 0.3% of In�x = 0, 4, 8, and 16Slide Number 20Thermoelectric Properties of n-type PbS� PbS-Bi2S3 phase diagramn-type PbSn-type PbS with second phasesn-type PbS with second phasesTEM: nanostructured PbSNanostructures n-type PbS, ZT=1.1Slide Number 28Conclusions