hiromi okubo for identifying and optimizing novel thermoelectric materials theoretical and...

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