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Solid State Chemistry Meets Physcis: Thermoelectric Materials
Solid State Chemistry Meets Physcis: Thermoelectric Materials
AN INTERDISCIPLINARY COLLABORATION
KANATZIDISMSU, CHEMISTRY
Solid State ChemistrySynthesis, Discovery
KANATZIDISMSU, CHEMISTRY
Solid State ChemistrySynthesis, Discovery
Ctirad UHERUniv of Michigan
Physics
Ctirad UHERUniv of Michigan
Physics
TIM HOGANMSU, E. ENGINEERING
MEASUREMENTS
S. D. MAHANTIMSU, PHYSICS
Theory
C. KANNEWURFNorthwestern Univ
E. Engineering
H. Schock, T. ShihMSU, Mechanical
EngineeringApplications
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Michigan State University…Michigan State University…
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THERMOELECTRIC POWER(Seebeck Coefficient)
ΔV Smeasured= ΔVΔT
Smeasured= Ssample-SCu
ΔT
Cu block
Cu blockheater
constantan
sample
zero current technique:extremely useful probefor investigation ofintrinsic conduction in granular or polycrystallinematerials
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Thermoelectric ApplicationsThermoelectric Applications
Beverage cooler
Biological samples LASER diodeCooler
MicroprocessorCooler
www.tellurex.com
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Heat to Electric EnergyHeat to Electric Energy
Up to 20% conversion efficiency withright materials
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Thermoelectric BenefitsThermoelectric Benefits
• TE coolers have no moving parts, need substantially less maintenance.
• Life-testing has shown the capability of TE devices to exceed 200,000 hrs. of steady state operation.
• TE coolers contain no chlorofluorocarbons. • Temperature control to within fractions of a degree can
be maintained using TE devices. • TE coolers function in environments that are too
severe, too sensitive, or too small for conventional refrigeration.
• TE coolers are not position-dependent.
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How does it work?How does it work?
http://www.designinsite.dk
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Thermoelectric applicationsThermoelectric applications
• Air conditioning (distributed, environmentally friendly)
• Spot cooling of electronic chips, superconductors etc.
• Thermal suits for fire-fighting, soldier etc• Waste heat recovery (automobiles, utilities
etc)• Geothermal power generation
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Figure of MeritFigure of Merit
ZT =σ ⋅ S2
κ total
•T
σ ⋅ S2Power factor
Total thermal conductivity
electrical conductivity thermopower
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Today’s situationToday’s situation
• The most efficient materials today is Bi2Te3alloy
• ZT~0.8-1.0• Further improvements on Bi2Te3 are not
expected.• New materials are needed
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Thermoelectric Properties of Optimized Bi2Te3(e.g. Bi2-xSbxTe3, Bi2Te3-xSex) at Room Temperature
Thermoelectric Properties of Optimized Bi2Te3(e.g. Bi2-xSbxTe3, Bi2Te3-xSex) at Room Temperature
• S ~ ±220 µV/K• σ ~ 950 S/cm• ρ=1/σ ~ 1.1 mΩ·cm• κ ~ 1.5 W/m·K
• ZT ~ 1 !
ZT~1
T, K
ZT
300 400200
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Structure of Bi2Te3 and NaClStructure of Bi2Te3 and NaCl
xy
z
x
z
NaCl Bi2Te3 defect NaCl
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TYPICAL BEHAVIOR OF MATERIALS
S>50 µV/K
S>-50 µV/K
0<S<20 µV/K
-20 µV/K<S<0
T (K)
S (µV/K)S (µV/K)
T (K)
metal-likesemiconductor-like
p-type
n-type n-type
p-type
LARGE
SMALL
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Power Factor (S2*σ) vs Carrier Concentration
Power Factor (S2*σ) vs Carrier Concentration
Carrier Concentration, cm-1
1017 1018 1019 1020 1021
S2*σThermopower, Sconductivity
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Thermopower and Electronic Structure
• σ(E) is the electrical conductivity determined as a function of band filling or Fermi energy, EF. If the electronic scattering is independent of energy, σ(E)is just proportional to the density of states (DOS) at EF.
• For maximum S, a large asymmetry in the DOS and/or scattering within a few kTabove and below the Fermi energy is required.
S =π2kB
2T3e
d(lnσ(E))dE
E = EFMott Equation
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Band structure TypesBand structure Types
k
E
k
E
k
Ef
simple simple complex
�ZT and Band Structure
B =CT 5 / 2γ mxmym z
μx
κ latt
B- parameter
m= effective massµ= mobilityκlatt= lattice thermal conductivityT = temperatureγ= band degeneracy
High γ comes with(a) high symmetry e.g. rhombohedral, cubic(b) off-center band extrema
ZT
B-parameter
1.0 -
10 –
0.1 -
1.0 100.10.01
Γ X
Ene
rgy
VB
CB
Ef
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Desirable characteristicsDesirable characteristics
• Multiple peaks and valleys in valence/conduction band
• Heavy carrier masses• Flat bands
εε
k k
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Selection criteria for candidate materials
Selection criteria for candidate materials
• Narrow band-gap semiconductors• For operation at room temperature
• Heavy elements• High mobility, low thermal conductivity
• Large unit cell, complex structure• low thermal conductivity
• Highly anisotropic or highly symmetric• Complex compositions
• low thermal conductivity, electronic structure
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Important Issue: Thermal Conductivity
Important Issue: Thermal Conductivity
• Slack’s proposal: Phonon-Glass/ Electron-Crystal (PGEC)• Rattling Ions in the lattice: watch thermal
displacement parameters
o o o o
o o o oo
o
o
o
o
oooo o oooo o o
o o o o o
o
o
Rattling ions in cavities or tunnels scatter heat-carrying phonons
Crystalline solid
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Reaction ChemistryReaction Chemistry
• A2Q + PbQ + Bi2Q3 –––––> (A2Q)n(PbQ)m(Bi2Q3)p
A2Q
PbQBi2Q3
A=K, Rb, CsQ=Se, Te
K5Bi17Se28
β-K2Bi8Se13
Rb0.5Bi1.83Te3
Pb5Bi6Se14
A1+xPb4-2xBi7+xSe15
APb2Bi3Te7
Pb6Bi2Se9 Pb5Bi12Se23
Map generates target compounds
CsBi4Te6
Investigating the System:
Phases shownare promising new TEMaterials
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K ions possess ~2x the thermal displacement parameter of the Bi/Se framework
K2Bi8Se13
x y
z
Se
Bi
K
β-K2Bi8Se13this block is a chunk from the NaCl lattice
8,9-coordinate sites K, Bi
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NaCl Structure: The Basic “Raw” Material
NaCl Structure: The Basic “Raw” Material
NaCl Lattice
“Modules” are cut out of NaCl stock
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β-K2Bi8Se13β-K2Bi8Se13
0
20
40
60
80
100
0 50 100 150 200 250 300
Con
duct
ivity
(S/c
m)
Temperature (K)
-400
-300
-200
-100
0
0 50 100 150 200 250 300 350
Ther
mop
ower
(µV
/K)
Temperature (K)
-400
-350
-300
-250
-200
-150
-100
-50
0
0 50 100 150 200 250 300
Ther
mop
ower
(µV
/K)
Temperature (K)
150
200
250
300
350
400
0 50 100 150 200 250 300
Con
duct
ivity
(S/c
m)
Temperature (K)
Sn Doped
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β-K2Bi8Se13 : Room temp ZT=0.9. At 600 K estimated at 1.5 (to be verified)
β-K2Bi8Se13 : Room temp ZT=0.9. At 600 K estimated at 1.5 (to be verified)
10
15
20
25
30
35
40
45
0.45 0.5 0.55 0.6 0.65 0.7 0.75
α/S
(arb
itrar
y un
it)
Eg = 0.59 eV
β-K2Bi
8Se
13
Energy (eV)
-250
-200
-150
-100
-50
0
0 50 100 150 200 250 300
β-K2Bi
8Se
13
Thermopower (μV/K)
Temperature (K)
DY61243 ingot
0
500
1000
1500
2000
2500
3000
0 50 100 150 200 250 300 350
Conductivity (S/cm)
Temperature (K)
0
1
2
3
4
5
6
0 50 100 150 200 250 300
β-K2Bi
8Se
13
κ (W
/m. K
)
Temperature (K)
DY61243 ingot
Uher et al
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Sn Doping in β-K2Bi8Se13Sn Doping in β-K2Bi8Se13
-350
-300
-250
-200
-150
-100
-50
0
0 50 100 150 200 250 300
Undoped0.5% Sn1.0% Sn1.5% Sn2.0% Sn3.0% Sn
wer
(µV
/K)
Temperature (K)
0
5
10
15
20
25
30
35
40
0 50 100 150 200 250 300
Undoped0.5% Sn1.0% Sn1.5% Sn2.0% Sn3.0% Sn
ower
Fac
tor S
2 σ
(µW
/cm
·K
2)
Temperature (K)
0
0.2
0.4
0.6
0.8
1.0
0 50 100 150 200 250 300
Undoped0.5% Sn1.0% Sn1.5% Sn2.0% Sn3.0% Sn
ZT
Temperature (K)
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Michigan State University /Tellurex Corp. Collaboration
Michigan State University /Tellurex Corp. Collaboration
β-K2Bi8Se13
New TE material grown at MSU
New TE material grown at Tellurex
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Photo of the first TE module containing 63 couples n-β-K2Bi8Se13/p-Bi2Te3
Photo of the first TE module containing 63 couples n-β-K2Bi8Se13/p-Bi2Te3
UnoptimizedΔT=36 oCTh=50 oCAll materials grownat Tellurex Inc
�x
y
z xy
z
α-K2Bi8Se13 versus β-K2Bi8Se13α-K2Bi8Se13 versus β-K2Bi8Se13
α-K2Bi8Se13, Eg=0.76 eV β-K2Bi8Se13, Eg=0.59 eV
Mixed K,Bi
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α-, β-K2Bi8Se13 : Electronic structureα-, β-K2Bi8Se13 : Electronic structure
n-type character
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Quenched and annealed β-K2Bi8Se13Quenched and annealed β-K2Bi8Se13
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Abs
orpt
ion
Energy, eV
after annealingquenched
Eg=0.59 eV
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CsBi4Te6CsBi4Te6
xy
z
C 2/m
51 Å
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“Undoped” as-prepared material“Undoped” as-prepared material
0
20
40
60
80
100
120
0
5
10
15
20
0 50 100 150 200 250 300
S (µ
V/K
) κ (W/m
-K)
Temperature (K)
DY72121
0
50
100
150
200
250
300
350
0 50 100 150 200 250 300
dy72121(CsBi4Te6 crystal)
Con
d. (S
/cm
)
Temperature (K)
conductivity thermopower
Thermal conductivity
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Crystals of CsBi4Te6Crystals of CsBi4Te6
1 mm1 mm
100 µm
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Doped CsBi4Te6Doped CsBi4Te6
0
1000
2000
3000
4000
5000
6000
7000
8000
0
50
100
150
200
0 50 100 150 200 250 300 350
SbI3 doped CsBi
4Te
6
Con
duct
ivity
(S/c
m) S
eebeck (µV/K
)
Temperature (K)
At 260 K: S ~174 µV/KCond. ~1400 S/cm
κ ~14 mW/cm-K
ZTmax
~0.8
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Thermal Conductivity of p-type CsBi4Te6
Thermal Conductivity of p-type CsBi4Te6
0.0
1.0
2.0
3.0
4.0
5.0
6.0
0 50 100 150 200 250 300 350
κ (W
/m. K
)
Temperature (K)
parallel to needle
perpendicular to needle
Data by Uher et al
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Doping with SbI3Doping with SbI3
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CsBi4-xSbxTe6 x = 0.3
SbSbBiBi
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CsBi4Te6CsBi4Te6
0.0
0.2
0.4
0.6
0.8
1.0
0.0
0.2
0.4
0.6
0.8
1.0
0 50 100 150 200 250 300 350
Figure of Merit (ZT)
CsBi4Te
6 doped
p-Bi2Te
3 Marlow
ZT
Temperature (K)
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Best TE MaterialsBest TE Materials
0
0.2
0.4
0.6
0.8
1
0 200 400 600 800 1000 1200 1400
n-BiSb �
n-SiGe sintered
CsBi4Te
6
LaFe3CoSb
12
Bi2Te
3
PbTe
ZT
Temperature (K)
RT
Temperature (K)
ZT
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ConclusionsConclusions
• The strategy to search for new materials in the (A2Q)n(PbQ)m(Bi2Q3)p (Q=Se, Te) system is successful
• Many new promising compounds identified• All compounds strongly anisotropic• Doping studies are important in ZT optimization• ZT for β-K2Bi8Se13 ~0.7 at rt, higher at >400K
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ReferencesReferences• “The Role of Solid State Chemistry In The Discovery of New
Thermoelectric Materials” Mercouri G. Kanatzidis, Semiconductors and Semimetals, 2000, 69, 51-100.
• Slack,G. A. “New Materials and Performance Limits for Thermoelectric Cooling” in CRC Handbook of Thermoelectrics" Edited by Rowe, D. M. CRC Press, Boca Raton, 1995, pp. 407-440
• Tritt T. M. "Thermoelectrics run hot and cold", Science. 1996, 272, 5266, 1276-1277.
• Mahan, G. D. “Good thermoelectrics” Solid State Phys: 1998, 51, 81-157. (c) DiSalvo, F. J. "Thermoelectric cooling and power generation", Science. 1999, 285 5428, 703-706
• Thermoelectric Materials 1998- The Next Generation Materials for Small-Scale Refridgeration and Power Generation Applications, edited by Tritt, T. M.; Kanatzidis, M. G.; Mahan, G. D.; Lyon, Jr., H. B. Mat. Res. Soc.Symp. Proc. 1999, Vol. 545, 233-246.
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CollaboratorsCollaborators
Prof. Tim Hogan, Dept of Electrical Engineering, MSUProf. S. D. (Bhanu) Mahanti, Dept. of Physics, MSUProf. Carl R. Kannewurf, Dept of Electrical Engineering, Northwestern Univ.Ctirad Uher, Dept. of Physics, U of MArt Schultz, Argonne NL
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TE Research groupTE Research group
• Dr Duck young Chung• Dr Antje Mrotzek• Dr Kuei fang Hsu• Lykourgos Iordanidis• Kyoung-shin Choi• Jun-Ho Kim• Sandrine Sportouch• Rhonda Patschke
• Tim McCarthy• Dr. Jun-Huan Do
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AcknowledgementsAcknowledgements• Dr. Antje Mrotzek• Lykourgos Iordanidis• J. A. Aitken• Jun-Ho Kim• Joseph Wachter• Marina Zhuravleva• Xuini Wu• Jim Salvador• Brad Sieve• R G Iyer• Dr. Theodora Kyratsi• Dr. J.-H. Do• Dr. Duck Young Chung• Dr. Servane Coste• Dr. Pantelis Trikalitis• Dr. Susan Latturner• Dr. Kuei-fang Hsu