Direct Energy Conversion: Chemistry,
Physics, Materials Science and
Thermoelectrics
Mercouri G Kanatzidis
KANATZIDIS
KANATZIDIS
MSU,CHEMISTRY
CHEMISTRY
MSU,
SolidState
StateChemistry
Chemistry
Solid
Synthesis,Discovery
Discovery
Synthesis,
S. D. MAHANTI
MSU, PHYSICS
Theory
TIM HOGAN
MSU, E. ENGINEERING
Measurements, Devices
CTIRAD
CTIRAD UHER
UHER
Univ
Univ of
of Michigan
Michigan
Physics
Physics
Measurements
Measurements
American Physical Society Meeting, Baltimore March 2006
MURI
HAROLD SCHOCK
MSU, Mechanical
Engineering
Applications
ELDON CASE
MSU, Mechanical
Engineering
Metallurgy
Heat to Electrical Energy Directly
Up to 20% conversion efficiency with right materials
http://www.dts-generator.com/
Schock group
Thermoelectric applications
„
Waste heat recovery
• Automobiles
• Over the road trucks
• Utilities
• Chemical plants
„
Space power
Remote Power
Generation
Solar energy
Geothermal power
generation
Direct nuclear to electrical
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U.S. Energy Flow, 1999
web site: www.eia.doe.gov
Given that ~60% of energy becomes waste heat, even a 10% capture and conversion
to useful forms can have huge impact on overall energy utilization
How does it work?
http://www.designinsite.dk
TE devices have no moving parts, no noise, reliable
Figure of Merit
0.25
δ = 0.0
δ = 0.1
0.2
electrical conductivity
0.15
σ⋅S
ZT =
•T
κ total
δ = 1.1
η
2
0.1
0.05
Total thermal conductivity
0
0
0.5
1
1.5
ZT
2
2.5
3
avg
δ=Rc/R
thermopower
For Th = 800K
Tc = 300K
Power factor
σ⋅S
2
Today’s situation
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The most efficient materials today
for power generation: PbTe and
TAGS (TeSbGeAg alloy)
The most efficient material for
cooling Bi2Te3
„Quantum Dot Layers in thin
MBE-grown PbSe/PbTe
PbTe: ZT~0.8 at 800 K (n-type)
superlattices (Harman et al,
TAGS: ZT~1.2 700 K (p-type)
ZT~3)
Bi2Te3-xSex: ZT~1 at 300 K
Further improvements are needed.
PbTe
New materials needed
PbSe 20 nm dot
Hicks LD, Dresselhaus MS Phys. Rev. B 47 1993 (24): 16631
Some promising systems under
investigation
half-Heusler alloys (ZrNiSn)
„ Zn4Sb3
„ Clathrates
„ Skutterudites (CoSb3)
„ Bulk nanocomposites based on PbTe
„ Bulk nanocomposites based on Si-Ge
„ AgSbTe2/PbTe, NaSbTe2/PbTe
„
See March 2006 issue of MRS Bulletin
ZT and Electronic Structure
Isotropic structure
Anisotropic structure
mx m y
T τ
mz
3/ 2
Z max
∝γ
e
κ latt
m= effective mass
τ=scattering time
r= scattering parameter
κlatt= lattice thermal conductivity
T = temperature
(r +1/ 2 )
For acoustic phonon scattering
r=-1/2
E
E
γ= band degeneracy
Large γ comes with
(a) high symmetry e.g.
rhombohedral, cubic
(b) off-center band extrema
Ef
k
k
k
Complex electronic structure
Selection criteria for candidate
materials
„
„
Narrow band-gap semiconductors
Heavy elements
ƒ High µ, low κ
„
Large unit cell, complex structure
ƒ low κ
„
„
Highly anisotropic or highly symmetric…
Complex compositions
ƒ low κ, complex electronic structure
Chemistry as a source of materials
Investigating the System:
A2Q + PbQ + M2Q3 –––––> (A2Q)n(PbQ)m(M2Q3)p
Map generates target compounds
Cubic materials
ABmMQ2+m
A=Ag, K, Rb, Cs
M=Sb, Bi
Q=Se, Te
A2 Q
Phases shown
are promising new TE
Materials
Rb0.5Bi1.83Te3
APb2Bi3Te7
A1+xPb4-2xBi7+xSe15
PbQ
Pb6Bi2Se9
Pb5Bi6Se14 Pb5Bi12Se23
β-K2Bi8Se13
CsBi4Te6
Bi2Q3
Our first contact with cubic AgPbmSbTe2+m
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AgBi3S5, KPbBi9Se13, KPb4Sb7Se15
CsPbBi3Te6, CsPb2Bi3Te7, CsPb3Bi3Te8,
RbPbBi3Te6, RbPb2Bi3Te7, RbPb3Bi3Te8,
KPbBiSe3, K2PbBi2Se5
K2Pb3Bi2Te7, KPb4SbTe6
AgPbmSbTe2+m (LAST-m)
AgPbm(Sb,Bi)Te2+m (BLAST-m)
Pb
Te
Sb
Ag
Unit cell volume (Å)
268
267
266
265
264
Vegard's law
263
6
8
10
12
14
16
18
m value
(1) (a) Rodot, H. Compt. Rend. 1959, 249, 1872-4.
(2) (a) Rosi, F. D.; Hockings, E. S.; Lindenblad, N. E. Adv. Energy Convers. 1961, 1, 151.
(LAST-18) Ag1-xPb18SbTe20: Tunable properties
Changing x
0.8
Comparison of Thermopower
0.7
Ag0.73 (KF2207R2b)
Ag0.76 (KF2228R3A2)
Ag0.78 (KF2213R1B)
Ag0.80 (KF2213R2C)
Ag0.82 (KF2229R1A)
Ag0.82 (KF2229R1B)
Ag0.82 (KF2229R1C)
Ag0.82 (KF2229R1D)
-50
-100
0.6
0.5
ZT
Thermopower (µ V/K)
0
-150
Comparison of ZT
Ag0.73 (KF2207R2b)
Ag0.76 (KF2228R3A2)
Ag0.78 (KF2213R1B)
Ag0.80 (KF2213R2C)
Ag0.82 (KF2229R1A)
Ag0.82 (KF2229R1B)
Ag0.82 (KF2229R1C)
Ag0.82 (KF2229R1D)
0.4
0.3
0.2
-200
0.1
-250
50
100
150
200
250
300
350
400
450
Temperature (K)
30
2
2
Power Factor S σ (µW/cm K )
Ag0.73 (KF2207R2b)
Ag0.76 (KF2228R3A2)
Ag0.78 (KF2213R1B)
Ag0.80 (KF2213R2C)
Ag0.82 (KF2229R1A)
Ag0.82 (KF2229R1B)
Ag0.82 (KF2229R1C)
Ag0.82 (KF2229R1D)
20
10
0
50
100
150
200
250
300
Temperature (K)
120 160 200 240 280 320 360 400
Temperature, K
Comparison of Power Factors
50
40
0
80
350
400
450
Synthesis: Heating cooling profiles
rock
T, K
950-1000 ºC
Cool to 50 ºC in
72 h
13 deg/h
Ingot properties very sensitive to cooling profile
Gravity induced inhomogeneity
LAST-18
time, h
1000 ºC
rock
T, K
Cool to 50 ºC
in 24 h
time, h
Wernick, J. H.. Metallurg. Soc. Conf. Proc. (1960), 5 69-87.
R. G. Maier Z. Metallkunde 1963, 311
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Strongly varying
composition from top to
bottom.
Strongly varying
properties from top to
bottom.
“Sweet” spot exists with
very high ZT.
Mechanical properties
weak.
m= 8
m= 14
m= 18
σ (S/cm)
„
S (µV/K)
Samples cooled slowly from
liquid to solid
m= 25
m= 40
Strong composition grading along ingot
Properties of Ag1-xPb18SbTe20
2.5
2000
Lattice thermal conductivity
-150
1500
-250
1000
-300
500
-350
0
300
-400
350
400
450
500
550
600
650
S (µV/K)
σ (S/cm)
-200
Lattice Thermal Conductivity (W/mK)
-100
2
PbTe
1.5
1
LAST-18
0.5
0.35 W/mK (Harman PbTe/PbSe superlattice)
700
0
Temperature, K
300
400
500
600
Temperature (K)
700
800
Ag1-xPb18SbTe20
2.00
Ag
Pb SbTe
0.86
18
20
ZT
1.50
1.00
0.50
0.00
300
350
400
450
500
550
600
650
700
Temperature, K
Hsu KF, Loo S, Guo F, Chen W, Dyck JS, Uher C, Hogan T, Polychroniadis EK, Kanatzidis MG Science, 2004, 303, 818
What is the origin of the TE
properties of AgPbmSbTem+2
systems?
HRTEM
Coherently embedded nanocrystals
Pb- rich region
8-10 nm
Ag-Sb rich region
Polychroniadis, Frangis, 2004
LAST-18 κlatt=1.2 W/m-K at 300 K
PbTe κlatt=2.2 W/m-K at 300 K
Coherent compositional fluctuations in
AgPbmSbTem+2
FCC lattice
10 nm
Ag, Sb, Pb ordering
Driving force for segregation
Ag+/Sb3+ pair: stable
Ag
Te
Te
Pb
Te
Pb
Pb
Te
Pb
Te
Ag
Pb
Te
Te
Pb
Pb
Te
Pb
Pb
Te
Te
Sb
Te
Te
Pb
Te
Pb
Te
Pb
Te
Pb
Pb
Te
Sb
Te
Pb
Te
Pb
Te
Te
Ag
Pb
Te
Sb
Te
Pb
Pb
Te
Te
Te
Te
Te
Pb
Pb
Te
Pb
Dissociated state..unstable
Pb
Pb
Te
Pb
Te
Pb
Te
Te
Pb
Te
Pb
Te
Ag
Te
Pb
Te
Sb
Te
Pb
Te
Pb
Te
Te
Pb
Pb
Te
Pb
Associated state..stable
Any +1/+3 pair
Te
Solid solutions in (AgSbTe2)1-x(PbTe)x
LAST-m
0
20
40
60
80
100
Thermal
Conductivity(mW/cm·K)
(W/cmK)
LatticeLattice
Thermal
Conductivity
20
Klemmens-Drabble theory
18
m=65
16
14
m=62
m~62
12
Random alloy
m~30
10
m=18
8
m=10
6
Experimental Points
below theoretical
4
0
AgSbTe2
m=18
20
T. Irie Jap. J. Appl. Phys. 1966, 5, 854
40
60
Mol % PbTe
80
100
PbTe
P-type materials, LASTT
1000
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12000
Ag0.3Pb7Sn3Sb0.1Te12
10000
8000
6000
4000
2000
0
20
30
40
50
60
2Theta
70
80
90
100
2 hours
rocking
800
o
Temperature ( C)
„
(LASTT-m) Ag(Pb1-xSnx)mSbTe2+m
Sn atoms act as acceptors
Ag atoms act as acceptors
Sb atoms act as donors
e.g AgPb10Sn8SbTe20,
AgxPb7Sn3SbyTe12,
Very low lattice thermal conductivity
Good homogeneity
Intensity (arb. units)
„
600
400
200
0
0
10
20
30
t (hours)
40
50
60
LASTT-16
Very low lattice thermal conductivity
κlatt =0.5 W/m·K at 650 K
Androulakis, Hsu, Hogan, Uher, Kanatzidis Advanced Mater. 2006, in press
LASTT-16: AgPb12Sn4Sb0.4Te20
320
280
Seebeck (uV/K)
240
200
160
120
80
40
0
320
400
480
560
T e m p e ra tu re , K
640
720
Androulakis, Hsu, Hogan, Uher, Kanatzidis Advanced Mater. 2006, in press
Figure of Merit LASTT (p-type)
2.0
1.8
Ag0.5 Pb6 Sn2 Sb0.2 Te10
1.6
Ag0.9 Pb5 Sn3 Sb0.7 Te10
(b)
Ag0.6 Pb7 Sn3 Sb0.2 Te12
1.4
LASTT
ZT
1.2
TAGS
1.0
0.8
0.6
PbTe
0.4
0.2
0.0
300
400
500
600
700
800
Temperature (K)
Androulakis, Hsu, Hogan, Uher, Kanatzidis Advanced Mater. 2006, in press
(A)
Lattice Thermal conductivity (W/mK)
NaPb20SbTe22 (SALT-20)
2
(B)
1.5
1
0.5
0
Pb Sn Te
0.9
0.1
not-nano
PbTe Se
0.9
0.1
Na Pb SbTe
1-x
20
22
nano
300 350 400 450 500 550 600 650 700
Temperature, K
50 nm
Poudeu, Hogan, Kanatzidis Angew. Chemie, 2006,
SALT-20
Poudeu, Hogan, Kanatzidis Angew. Chemie, 2006,
State of the art - bulk
2.5
2
LAST
NaPb SbTe
20
22
LASTT
1.5
ZT
TAGS
Tl BiTe
9
1
CsBi Te
4
6
6
Ce Fe CoSb
Bi Te
2
0.9
3
3
12
SiGe
PbTe
0.5
0
0
200
400
600
800
Temperature, K
1000
1200
1400
Conclusions
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New approaches are succeeding in raising ZT
The (A2Q)n(PbQ)m(Bi2Q3)p (Q=Se, Te) system is a
rich source of new materials
Several new promising compounds identified
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ƒ
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LAST, LASTT and SALT family of materials
ƒ
ƒ
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strongly anisotropic
cubic
nanostructured
nanostructured
superior ZT
Strong thermal conductivity reduction achieved
through nanostructuring
Doping studies and processing conditions are
important in ZT optimization
Outlook
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Further progress is expected on the TE figure of merit
Fundamental challenge:
•
•
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Research in new materials should focus on
•
•
•
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Translate current theoretical physical predictions on how to enhance
Power Factor (σ·S2) into actual chemistry in the laboratory
Achieve minimum thermal conductivity (~0.3 W/mK) in a bulk
(nano)crystalline TE material
Understanding and controlling carrier scattering
Controlling nanostructuring to manipulate phonon propagation
Discovering new compounds
Long term: Waste heat recovery and conversion could be impacted
on a massive scale with low cost materials if ZT>2-3.
Thermoelectrics could help utilize existing depletable energy
resources more effectively
Thermoelectrics could also play role in renewable energy (e.g. solar,
etc)
Collaborators
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Tim Hogan, Dept of Electrical
Engineering, MSU
S. D. (Bhanu) Mahanti, Dept. of
Physics, MSU
Ctirad Uher, Dept. of Physics, U of
Michigan
Simon Billinge, Physics, MSU
Eldon Case, MSU
Harold Schock, MSU
Bruce Cook, Iowa State
Terry Tritt, Clemson U
Art Schultz, Argonne NL
TE Research group
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Dr Duck young Chung
Joseph Sootsman
Dr Kuei fang Hsu
Dr Eric Quarez
Aurelie Guegen
Ferdinand Poudeu
Jun-Ho Kim
Dr John Androulakis