Hiromi Okubo

1. Theoretical Theoretical and and Computational Approaches Computational Approaches for Identifying and Optimizing Novel Thermoelectric Materials for Identifying and Optimizing Novel Thermoelectric Materials David J.Singh Hiromi Okubo

2. Thermoelectric Effect Thermoelectric Effect The Seebeckeffect The Peltiereffect The Thomson effect Products Advantage Performance index ZT ZT Performance index Guideline of Design Guideline of Design CHEVREL PHASES Mo8Se6 Industrial material Bi2Te3/Sb2Te3 Future Future

3. Thermoelectric Effect Thermoelectric Effect Seebeck effect Peltier effect Seebeck effect Peltier effect In Thomas seebeck １８２３ A temperature gradient A voltage drop T T C C T T V H H Q＝π・ I V＝S・ΔT V Seebeck coefficient Peltiercoefficient π＝ TS

4. Peltier device

5. Advantage Energy and environmental issues ・Generation by waste heat ・longevity ・Cooling without Freon ・maintenance free Products • Mobile refrigerator in the car • Cooling machine of the CPU of the computer • Thermoelectricity watch Exhaust gas Heat generation from the engine

6. ZT Performance index 2 S σ Figure of Merit Electric conductivity = Z Seebeck coefficient  Thermal conductivity A.F.Ioffe, semiconductor Thermoelements and Thermoelectric cooling , Infosearch Ltd London(1957)

7. ZT Performance index 2 Ohm's law S σ Fourier's law Electric conductivity = Z Seebeck coefficient  Thermal conductivity A.F.Ioffe, semiconductor Thermoelements and Thermoelectric cooling , Infosearch Ltd London(1957)

8. ZT Performance index 2 S σ Electric conductivity = Z Seebeck coefficient  Thermal conductivity A.F.Ioffe, semiconductor Thermoelements and Thermoelectric cooling , Infosearch Ltd London(1957)

9. Band Theory ＋ Boltzmann equation Conductivity tensor

10. ZT Performance index 2 S σ Figure of Merit Electric conductivity = Z Seebeck coefficient  Thermal conductivity A.F.Ioffe, semiconductor Thermoelements and Thermoelectric cooling , Infosearch Ltd London(1957)

11. σ 2 S Metals = Z • low Seebeck coefficient • large electronic contribution to the thermal conductivity σ  2 S σ Insulators • large Seebeck coefficient  • small electronic contribution to the thermal conductivity S • Too few carriers semiconductor Carrier concentration A carrier concentration of about 1019cm-3

12. G Large S ε

13. G Large S ε

14. Large S G ε Low dimension Large S

15. Low  • A large number of atoms in the unit cell • A large average atomic mass • Cagelike structures in which a weakly bound atom or molecule in the cage“rattles”

16. Guideline of Design semiconductor Between metal and insulator σ S 2 A carrier concentration of about 1019cm-3 σ Cagelike structures Low dimension • A large atomic mass Layered material  Low  Large S S Carrier concentration

17. BiTe SbTe Industrial material 2 3 2 3 / ZT=1 Refrigerator Carnot efficiency ZT=1 about 10% Carnot efficiency ZT=3 About 30% 4

18. ZT Performance index • ZT = f(βEg,B) γ The degeneracy of the band extrema • 3 • 2 The carrier mobility The density of states band mass •  • B = N・μ・m ＊ • ( ) • ph G.D.MAHAN SOILD STATE PHYSICS,vol,51 P81

19. CHEVREL PHASES Large voids in the crystal structure Chalcogen S Se Te MoX 6 8

20. Pb CHEVREL PHASES A large atomic mass • Low Large voids in the crystal structure Metal Mo X MMoX 6 8 6 8

21. CHEVREL PHASES LAPW method (linearized augmented plane wave method) - Mo Se p d - Mo Mo d d Mo Se 6 8

22. CHEVREL PHASES LAPW method (linearized augmented plane wave method) degeneracy flat Mo Se 8 6

23. CHEVREL PHASES LAPW method (linearized augmented plane wave method) degeneracy flat Doping N-type Mo Se 8 6

24. CHEVREL PHASES LAPW method (linearized augmented plane wave method) degeneracy flat Doping N-type Mo Se 8 6

25. Future Future Layered material and Low dimensional compound Thermoelectric calculation and material Design A calculation of the figure of merit ZT based on Bloch- Boltzmann Formula used First-principles studies