C A E S A R

Anthony Powell

Department of Chemistry

Heriot-Watt University

Edinburgh EH14 4AS

a.v.powell@hw.ac.uk

C A E S A R

Designing Next-Generation

Thermoelectric Materials for

Energy Harvesting

www.energy.hw.ac.uk/docs/CAESAR_Leaflet.pdf

Thermoelectric Energy Recovery

Thermoelectric Couple

Body to be cooled

Heat sink

p-type n-type h+ e-

+ -

0V

Body to be cooled

Heat sink

p-type n-type

+ -

Body to be cooled

Heat sink

p-type n-type

+ -

Body to be cooled

Heat sink

p-type n-type

+ -

Body to be cooled

Heat sink

p-type n-type

+ -

Body to be cooled

Heat sink

p-type n-type

+ -

Body to be cooled

Heat sink

p-type n-type

+ -

Body to be cooled

Heat sink

p-type n-type

+ -

Body to be cooled

Heat sink

p-type n-type

+ -

Body to be cooled

Heat sink

p-type n-type

+ -

Body to be cooled

Heat sink

p-type n-type

+ -

Body to be cooled

Heat sink

p-type n-type

+ -

Body to be cooled

Heat sink

p-type n-type

+ -

Body to be cooled

Heat sink

p-type n-type

+ -

Body to be cooled

Heat sink

p-type n-type

-

+ -

Body to be cooled

Heat sink

p-type n-type

h+ e-

+ -

T+ T

T

Power Generation

Lightweight and small

Very reliable

C A E S A R

Energy from Waste Heat

Thermoelectric

Generator

Recent programs:

GM

BMW

VW

200 - 600W TEG

ca. 5% Fuel Economy

New car emission standards

160 g CO2/km (2007)

130 g CO2/km (2012)

95 g CO2/km (2020) Regulation (EC) No 443/2009 (2009)

80% reduction in greenhouse gas

emissions(from 1990 levels) by 2050 UK Climate Change Act (2008)

C A E S A R

Energy Conversion Technologies

Zebarjadi et al, Energy Env. Sci., 5, 5147, (2012)

C A E S A R

Limitations of Current Materials

400 600 800 1000 1200 1400 16000

10

20

30

40 Z=0.005Z=0.004Z=0.003

Z=0.002

Eff

icie

ncy/%

Hot-side temperature/K

Z=0.001

)(

2

eL

TSZTFigure of Merit:

0 200 400 600 800 1000 1200 14000.0

0.4

0.8

1.2

1.6

2.0

Yb0.19

Co4Sb

12

AgPbmSbTe

2+m

PbTe

Bi2Te

3

CeFe4-x

CoxSb

12

ZT

Temperature/K

Si1-x

Gex

C A E S A R

Materials Parameters

Electrical conductivity ( ), Seebeck (S) and electronic

thermal conductivity ( e) all inter-dependent

S2

S

ln(n)

S

ln(n)

Insulators Metals

e

L

Semiconductors Hg

Cd

Au

Ag

Pt

Pd

Ir

Rh

Os

Ru

Re

W

Mo

Ta

Nb

Hf

Zr

La

Y

Rn

Xe

KrI

Br

Te

Mg

Se

Bi

Sb

As

Pb

Sn

Ge

Tl

In

GaZn

CuNiCo

FeMnCr

V

Ti

Sc

Mg

Ne

C

NF

O

Ar

ClSP

SiAl

Ba

Sr

Ca

Cs

Rb

K

MgNa

NaTerrestial Abundance

Te: 1 ppb by weight

Requires conduction of electricity like a metal and

conduction of heat like an insulator

)(

2

eL

TSZTFigure of Merit:

C A E S A R

Materials Design:

Phonon Glass Electron Crystal

Rattling vibrations reduce ph

CoSb3: 9 Wm-1K-1

R(Fe3CoSb12): 1.2 Wm-1K-1

Filled Skutterudites HWU-Cardiff Skutterudite Module

YbxCo4Sb12 (n-type)

CexFe3CoSb12 (p-type)

3 W cm-3 at ΔT 300 K (Tcold = 293 K)

Compares favourably with Bi2Te3

(3 W cm-3 at ΔT 100 K (Tcold = 293 K))

C A E S A R

Nanostructured Thermoelectrics

Quantum Confinement: Enhances S

Density of States

Energ

y

3D bulk

Density of States

Energ

y

2D Quantum Well

Energ

y

Density of States

1D Quantum Wire

Interface Scattering: Decreases L

Phonon mfp

Electron mfp

Interface

scattering when

mean-free-path >

interface spacing

Minnich et al

Energy Env.

Sci., 2, 466,

(2009)

C A E S A R

Ball-Milled Thermoelectrics

Bulk Nanostructured

Material ZTmax Temperature at

which ZTmax is

observed

ZTmax Temperature at

which ZTmax is

observed

Si 0.2 1200 0.7 1200

Si80Ge20 (n-type) 1.0 1200 1.3 1173

Si80Ge20 (p-type) 0.7 1200 0.95 1073

(Bi,Sb)2Te3 0.9 293 1.4 373

CoSb3 0.45 700 0.71 700

Vaqueiro and Powell, J. Mater. Chem. , 20, 9577, (2010)

(Bi,Sb)2Te3

Poudel et al, Science, 320, 634, (2008)

C A E S A R

Nanoinclusions in LAST-type Phases

A/B rich

Nanocluster

Pb rich matrix

Degenerate semiconductors

Nanoinclusions

Thermal conductivity

reduced from PbTe

LAST=18

n-type conduction

ZTmax = 2.2 at 800K

Silver deficient

Hsu et al, Science, 303, 818, (2004)

APbmBTem+2

C A E S A R

Tl1-xPbmBiTem+2

350 400 450 500 550 600 650 0.8

1.0

1.2

1.4

1.6

1.8 x= 0.0 x= 0.1 x= 0.2 x= 0.3

T/K

/W m

-1 K

-1

PbTe

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

ZT

@ 3

73K

Tl0.9Pb18BiTe12

Sam

ple

1

Sam

ple

2

Sam

ple

3

Hsu e

t al (2

004)

AgPb18SbTe20

0.00.1

0.20.3

0.1

0.2

0.3

0.4

0.5

0.6

0.7

m=18

m=10

x in Tl1-x Pb

m BiTem+2

ZT

@ 3

73

K

LA

ST

-18

Tl1-xPb18BiTe20

C A E S A R

Nanocomposite Materials Matrix Encapsulation

Heat Cool

PbTe - 2%Sb

Sootsman et al, Chem. Mater., 18, 4994, (2006) kL = 0.8 W m-1 K-1

liquid liquid

Heat

Solid A and solid B A melts B melts, A dissolves

in liquid B

B solidifies, A

insoluble in solid B,

so precipitates

C A E S A R

Solvothermal Growth of

Nanoparticulate Thermoelectrics Bi2Te3

Metal Salts,

Reducing agent

Solvent,

‘Template

Molecule’

T > Tb.p. PbTe

Fe0.5Ni0.5Sb3

P 200 bar

Mi et al. JALCOM, 399, 260, (2005)

Ji et al. J. Electron Mater., 36, 271, (2007)

C A E S A R

Superlattices and Layered Materials

50 Å Bi2Te3

Sb2Te3

10 Å

GaAs

Substrate

Phonon B

lockin

g

Ele

ctr

on

Tra

nsm

itting

Thin-Film Superlattices

κ = 0.22 W m-1 K-1

ZT = 2.4 @ 330 K Venkatasubramanian et al, Nature, 413, 597, (2001)

CsBi4Te6: ZT = 0.8 @ 225 K

Chung et al, JACS, 126, 6414, (2004)

rocksa

lt

type B

i 4Te

6-

Cs

+

C A E S A R

Layered Materials

BiO

+

CuS

e-

BiOCuSe ROZnSb

RO

+

ZnS

b-

co

vale

nt

ionic

Independent optimisation of S2 (covalent) and L (ionic)

C A E S A R

Pathways to Innovation

Adapted from http://www.lowcarboninnovation.co.uk

Research Councils

1 2

3

4

5

6

7

8

9

Basic R&D

Applied R&D

Demonstration Application

Technology Strategy Board

Energy Technologies Institute

The Carbon Trust

The European Union

Technology Readiness Level

Acknowledgements

Dr P. Vaqueiro (HWU)

Dr J-W Bos (HWU)

Dr A. Kaltzoglou (HWU)

Fabien Guinet (HWU)

Son Dac Luu (HWU)

Dr G. Min (Cardiff)

Prof. R.K. Stobart (Loughborough)

Prof. R. Jones (DSTL)