hiromi okubo for identifying and optimizing novel thermoelectric materials theoretical and...
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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
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
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
Peltier device
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
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
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
Z =S
2
Performance indexZTσ
A.F.Ioffe, semiconductor Thermoelements and Thermoelectric cooling , Infosearch Ltd London(1957)
Seebeck coefficient
Thermal conductivity
Electric conductivity
Boltzmann equation Band Theory＋
Conductivity tensor
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
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
G
ε
Large S
G
ε
Large S
G
ε
Large S
Low dimension
Large S
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
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
Bi
Te2 3
Sb
Te2 3/ ZT=1
about 10%ZT=1 Carnot efficiency
About 30%ZT=3 Carnot efficiency
4
Industrial material
Refrigerator
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
CHEVREL PHASESLarge voids in the crystal structure
Mo
X 6 8
Chalcogen
S Se Te
CHEVREL PHASESLarge voids in the crystal structure
M Mo X
Mo
X 6 8
6 8
A large atomic mass
Low
PbMetal
LAPW method (linearized augmented plane wave method)
CHEVREL PHASES
Mo Sed p-
Mo Mod d-
Mo
Se 8
6
LAPW method (linearized augmented plane wave method)
CHEVREL PHASESdegeneracy flat
Mo Se 8 6
LAPW method (linearized augmented plane wave method)
CHEVREL PHASESdegeneracy flat
Doping
N-type
Mo Se 8 6
LAPW method (linearized augmented plane wave method)
CHEVREL PHASESdegeneracy flat
Doping
N-type
Mo Se 8 6
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