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Hiromi Okubo
for Identifying and Optimizing Novel Thermoelectric Materials
TheoreticalandComputational Approaches for Identifying and Optimizing Novel Thermoelectric
Materials
TheoreticalandComputational Approaches
David J.Singh
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Future
Thermoelectric Effect The Seebeck
effectThe Peltier effect
Mo8Se6
Future
Advantage
Products
ZTPerformance indexZTPerformance index
Industrial material
CHEVREL PHASES
Thermoelectric Effect
The Thomson effect
Guideline of Design
Bi2Te3/Sb2Te3
Guideline of Design
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Seebeck effect
Seebeck effect
Thomas seebeck1823
A voltage dropA temperature
gradient
I n
V = S ・ΔT
Seebeck coefficient
V
Peltier effectPeltier effect
Q = π ・ I
Peltier coefficient
T H
V
TC
TH TC
Thermoelectric Effect
Thermoelectric Effect
π = TS
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Peltier device
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Advantage
・ longevity
・ maintenance free
・ Generation by waste heat・ Cooling without Freon
Products • Mobile refrigerator in the car
Heat generation from the engine
• Cooling machine of the CPU of the computer• Thermoelectricity watchExhaust gas
Energy and environmental issues
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Z =S
2
Performance indexZTσ
A.F.Ioffe, semiconductor Thermoelements and Thermoelectric cooling , Infosearch Ltd London(1957)
Figure of Merit
Seebeck coefficient
Thermal conductivity
Electric conductivity
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Z =S
2
Performance indexZTσ
A.F.Ioffe, semiconductor Thermoelements and Thermoelectric cooling , Infosearch Ltd London(1957)
Seebeck coefficient
Thermal conductivity
Electric conductivity
Ohm's law Fourier's law
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Z =S
2
Performance indexZTσ
A.F.Ioffe, semiconductor Thermoelements and Thermoelectric cooling , Infosearch Ltd London(1957)
Seebeck coefficient
Thermal conductivity
Electric conductivity
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Boltzmann equation Band Theory+
Conductivity tensor
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Z =S
2
Seebeck coefficient
Thermal conductivity
Performance indexZTσ Electric
conductivity
A.F.Ioffe, semiconductor Thermoelements and Thermoelectric cooling , Infosearch Ltd London(1957)
Figure of Merit
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Metals
Insulators
2
σ
S
Carrier concentration
σS
• low Seebeck coefficient• large electronic contribution to the thermal conductivity
• small electronic contribution to the thermal conductivity
• large Seebeck coefficient
• Too few carriers
2σS=Z
semiconductorA carrier concentration of about 1019cm-3
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G
ε
Large S
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G
ε
Large S
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G
ε
Large S
Low dimension
Large S
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Low
Cagelike structures in which a weakly bound atom or molecule in the cage “rattles”
A large average atomic mass
A large number of atoms in the unit cell
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Between metal and insulator
2
σ
S
Carrier concentration
σSsemiconductor
A carrier concentration of about 1019cm-3
Large S
Low Layered material
Low dimension Cagelike structures A large atomic
mass
Guideline of Design
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Bi
Te2 3
Sb
Te2 3/ ZT=1
about 10%ZT=1 Carnot efficiency
About 30%ZT=3 Carnot efficiency
4
Industrial material
Refrigerator
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γB = N ・μ ・
m
*3
2
( )
ph
The degeneracy of the band extrema
ZT = f
(βEg,B)The carrier mobility
The density of states band mass
Performance indexZT
G.D.MAHAN SOILD STATE PHYSICS,vol,51 P81
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CHEVREL PHASESLarge voids in the crystal structure
Mo
X 6 8
Chalcogen
S Se Te
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CHEVREL PHASESLarge voids in the crystal structure
M Mo X
Mo
X 6 8
6 8
A large atomic mass
Low
PbMetal
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LAPW method (linearized augmented plane wave method)
CHEVREL PHASES
Mo Sed p-
Mo Mod d-
Mo
Se 8
6
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LAPW method (linearized augmented plane wave method)
CHEVREL PHASESdegeneracy flat
Mo Se 8 6
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LAPW method (linearized augmented plane wave method)
CHEVREL PHASESdegeneracy flat
Doping
N-type
Mo Se 8 6
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LAPW method (linearized augmented plane wave method)
CHEVREL PHASESdegeneracy flat
Doping
N-type
Mo Se 8 6
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FutureFuture
A calculation of the figure of merit ZT
used First-principles studiesbased on Bloch- Boltzmann Formula
Layered material
Thermoelectric calculation and material Design
Low dimensional compound and