Palestra plenária do XII Encontro da SBPMat (Campos do Jordão, setembro/outubro de 2013). Palestrante: Mercouri G Kanatzidis - Northwestern University e Argonne National Laboratory (EUA).
Electrical power from heat: All-scale hierarchical thermoelectrics with and without earth-abundant materials.
1. Electrical power from heat: Allscale hierarchical thermoelectrics
with and without earth-abundant
materials
Mercouri Kanatzidis
Northwestern University
Sponsored by the
Department of Energy
7. Collaborators
Tim Hogan, MSU
S. D. (Bhanu) Mahanti, MSU
Ctirad Uher, Michigan
Simon Billinge, Columbia
Eldon Case, MSU
Vinayak Dravid, NU
Art Freeman, NU
Jos Heremans, OSU
Chris Wolverton, NU
Ray Osborn, Argonne
Stephane Rosenkranz, Argonne
Ken Gray, Argonne
David Seidman, NU
John Mitchell, Argonne
Duck Young Chung, Argonne
Theodora Kyratsi, U Cyprus
GROUP
Vinayak Dravid, NU
8. Seebeck Effect
Thermoelectricity - known in physics as the
"Seebeck Effect"
• In 1821, Thomas Seebeck, a German physicist,
twisted two wires of different metals together
and heated one end.
• Discovered a small current flow and so
demonstrated that heat could be converted to
electricity.
www.worldofenergy.com.au/07_timeline_w
orld_1812_1827.html
www.dkimages.com/discover/DKIMAGES/Discover/H
ome/Science/Physics-and-Chemistry/Electricity-andMagnetism/General/General-18.html
chem.ch.huji.ac.il/history/seebeck.html
9. Heat to Electrical Energy Directly
Up to 20% conversion efficiency with right materials
cold
hot
Thermopower S = ΔV/ΔT
TE devices have
no moving parts,
no noise, reliable
http://www.dts-generator.com/
10. Thermoelectric applications
• Waste heat recovery
• Automobiles
• Over the road trucks
• Marine
• Utilities
• Chemical plants
•
•
•
•
Space power
Remote Power Generation
Solar energy
Geothermal power
generation
• Direct nuclear to electrical
11.
12.
13. U.S. Energy Flow, 2009
http://www.eia.doe.gov/emeu/aer/
~65% of energy becomes waste heat,
~10% conversion to useful forms can have huge impact on overall energy utilization
14. Figure of Merit and Conversion Efficiency
electrical conductivity
thermopower
S
ZT
0.6
900 K
700 K
T
total
Total thermal conductivity
0.4
2
Power factor
S
0.2
Tcold= 300K
0.0
0.0 0.5 1.0 1.5 2.0 2.5 3.0
ZT
14
2
15. What about thermal conductivity?
• Diamond 1600 W/mK
• Cu 400 W/mK
• PbTe 2.2 W/mK
• Wood 0.2 W/mK
16. Why finding a “good thermoelectric” (ZT > 1) is
hard! Contra-indicated properties
Power factor
1.2
Seebeck, S
PF
0.9
conductivity,
, electronic
0.6
ZT
0.3
0.0
18
19
20
log n
21
S
2
T
“Power
factor”
19. What kinds of materials make
the best thermoelectrics?
Isotropic
structure
T
mx m y
mz
3/ 2
Z max
Anisotropic structure
e
r 1/ 2
For acoustic phonon scattering
r=-1/2
latt
m= effective mass
=scattering time
r= scattering parameter
latt= lattice thermal conductivity
T = temperature
= band degeneracy
Large comes with
(a) high symmetry e.g.
rhombohedral, cubic
(b) off-center band extrema
Complex electronic structure
19
21. Best thermoelectric materials
Developed new bulk thermoelectric materials with record ZTmax
n-type: ZTmax ~1.6 at 700K p-type: ZTmax ~1.7 at 700K 2
Pb Ag
18
0.86
SbTe
20
LAST
1.5
0.95
0.30
Ni
0.05
Co
3.95
12
La Te
2
2
0.4
Mg Si Sn
2
0.6
0.4
3
0.5
4
1
800 1000 1200
Temperature (K)
Bi Te
2
0.2
10
CeFe Sb
4
3
12
(AgSbTe )
3
2 0.15
Ce
0.28
PbTe
0.5
(GeTe)
0.85
Fe Co Sb
1.5
2.5
12
Hsu et al, Science, 303, 818 (2004)
Yb MnSb
14
400
600
11
800 1000 1200
Temperature (K)
Major discovery: self-assembled nanodots in bulk
materials responsible for record ZT’s
21
2
SiGe
0
600
6
Zn Sb
PbTe
400
22
Ag Pb Sn Sb Te
CoSb
3
0.5
0
0.6
20
3
ZT
ZT
Mg Si Sn
p-type Materials
p-type
Pb SbTe
1.5
Sb
2
Bi Te
Na
PbTe-PbS(8%)
Ba
1
2
n-type Materials
n-type
22. Endotaxial nanostructures
Endotaxy: Coherent lattice
matched placement of one crystal
inside another
Key aspects:
Interfaces
Strain
Band offsets
Stability
K. F. Hsu, etal Science 2004, 303, 818-821.
P. F. P. Poudeu, etal Angew. Chem. Int. Ed. 2006, 45, 3835-3839.
J. Androulakis, et al J. Am. Chem. Soc. 2007, 129 (31), 9780-9788.
K. Biswas, etal Nature Chemistry 2011, 3, 160-166.
K. Biswas, etal Nature, 2012, 419, 414-418.
matrix
23. electronic band structure of PbTe
Valence band is multiple
a≈6.45 Å (300K) peaks
m*Σ (~2m0) >> m*L(~0.2m0)
27. (c
VB
200
+++
+++
100
Valence bands of PbTe….
0
300
400
500
600
PbTe
700
T (K)
f
300
27
CB
24
200
2
150
100
21
18
15
6
300 400 500 600 700 800 900
T (K)
~0.30 eV
Thermal excitation of
holes to Σ band
12
9
50
E (eV)
250
S ( V/K)
T = 500 K
2
.S ( W/cmK )
e
PbTe
SrTe
VB
L
Σ
300 400 500
Heavy hole band
Light hole band 600 700 800 900
T (K)
Rising temperature
32. Thermal conductivity PbTe-x%SrTe
(S/cm)
2000
4% SrTe, 2% Na: SPS
2% SrTe, 2% Na: SPS
0% SrTe, 2% Na: SPS
4% SrTe, 2% Na: Ingot
2% SrTe, 1% Na: Ingot[14]
b 350
300
250
S ( V/K)
a 2500
1500
1000
200
150
100
500
0
50
30
(W/mK)
20
10
0
300 400 500 600 700 800 900
T (K)
d 4.4
total
2
2
S ( W/cmK )
c
0
300 400 500 600 700 800 900
T (K)
300 400 500 600 700 800 900
T (K)
f
4.0
3.6
3.2
2.8
2.4
2.0
1.6
1.2
0.8
300 400 500 600 700 800 900
T (K)
33. All length scales: record high ZT
Increasing efficiency
2.4
ZT ~ 1.1
2.0
ZT ~ 1.7
ZT ~ 2.2
Atomic
scale
4% SrTe, 2% Na: SPS
2% SrTe, 1% Na: Ingot[14]
0% SrTe, 2% Na: Ingot
Nano
scale
Meso
scale
ZT
1.6
1.2
All-scale hierarchical architecture
0.8
0.4
0.0
300
450
600
T, K
750
900
K. Biswas, Jiaqing He, I. D. Blum, C-I Wu, T. P. Hogan,
D. N. Seidman, V. P. Dravid & M. G. Kanatzidis
Nature 2012, 489, 414–418
1 cm
34. What is the proof that nanostructures
reduce thermal conductivity?
35. Model PbTe – PbS system for nanostructured TEs
Nucleation and Growth
ºC
1100
(PbTe)0.92(PbS)0.08
1000
900
800
Solid Solution
700
Spinodal
Decomposition
600
0
10
20
PbS
Miscibility Gap
30
40
50
mol. %
PbTe
Nucleation &
Growth
60
70
80
Chemical
Spinodal
90
100
PbTe
J. D. Gunton and M. Droz, Lecture Notes in Physics: Introduction to the Theory of Metastable and Unstable States, Vol. 183 (Springer-Verlag,
Berlin, Heidelberg, New York, Tokyo, 1983) pp. 1-13.
35
Leute, V., Volkmer, N. Z. Phys. Chem. NF., 144 1985, 145
36. PbTe0.92S0.08
Significant reduction in κlat
PbTe0.92S0.08
Solid solution
Solid solution
heat
(PbTe)0.92(PbS)0.08
Nanostructured
We can see the effect of nanoscale precipitation of PbS in situ
on the lattice thermal conductivity.
, W/mK
lat
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
~50% Reduction
in κlat
(PbTe)0.92(PbS)0.08
Run 1 Heating
Run 1 Cooling
Annealed Sample
300 400 500 600 700
Temperature, K
S. Girard, Jiaqing He
(PbTe)0.92(PbS)0.08
Nanostructured
37. Te free?
PbS: the cheapest thermoelectric
Nanostructuring PbS with second phases
42. Nanostructures n-type PbS, ZT=1.1
ZT ~ 1.1 @ 923 K
M: normal melting
B: Bridgman
Good repeatability !
S: SPS
ZT ~ 1.06 @ 923 K
BN coating
43. P-type Pb0.975Na0.025S-3%CaS/SrS
Both total and lattice κ were reduced by SrS inclusions
Pb0.975Na0.025S+3%SrS shows ZT about 1.2 at 923K,
Pb0.975Na0.025S+3%CaS shows ZT about 1.1 at 923K,
Zhao, L.-D. et. al., JACS. 133(2011)20476. & JACS. 134(2012)7902
44. TEM of Pb0.975Na0.025S -3%SrS
Fine grain size, Sr containing
precipitates, and no spot diffraction
splitting for Pb0.975Na0.025S-3% SrS.
crystallographic alignment between
PbS and SrS, strain maps and lattice
parameter difference at the interface
between PbS and SrS.
45. GROUP
Raising ZT of p-type PbS with endotaxial
nanostructuring and valence-band offset
engineering using CdS and ZnS
46. PbS is promising
GROUP
PbS is an ideal TE system because high performance in both n-type (ZT~1.1 at 923 K)
and p-type (ZT~1.1 at 923 K) can be achieved.
Zhao, L.-D. et. al., JACS. 133(2011)20476. & JACS. 134(2012)7902
n-type
p-type
Band gap energy levels of the metal sulfides, PbS, CdS, ZnS, CaS and SrS,
all in the NaCl structure
47. µ (cm2/V-sec)
mobility, μ at 920 K
PbS
CdS
GROUP
40 cm2/V-sec
ZnS
CaS SrS
4% MS
p-type, CdS containing sample shows higher μ
48. ZT for PbS system
~1.3 @923K
(a)
Eg
PbS
VB
E’g
minimal
valence band
offset
ΔE
CdS
0.13e
V
(b)
e
e
PbS
phonons
CdS
phonon-blocking/electron-transmitting
Zhao L.D. et al. JACS, 2012
GROUP
52. Conclusions
• A panoscopic view is required going forward
• Band alignment engineering between nanostructures and
matrix: ZT~2.2 at 900K
• 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 needed for continued
ZT increases
• High performance in nanostructured PbS (ZT~1.2-1.3 at 900 K)