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요약
ABSTRACT
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1. 서론 8
2. 이론적 배경 12
2.1 열전변환에 관한 물리적 현상 12
2.1.1 Seebeck effect 12
2.1.2 Peltier effect 12
2.1.3 Thomson effect 13
2.1.4 주울열과 열전도 15
2.2 열에너지 변환 16
2.2.1 열전발전 16
2.2.2 열전냉각 18
2.3 Bi2Te3계 열전재료 21
2.3.1 Bi2Te3계 화합물의 결정구조 21
2.3.2 Bi2Te3계 화합물의 결함구조 24
2.4 열전특성의 최적화 26
2.4.1 carrier 농도의 최적화 26
2.4.2 열전도도의 최소화 28
2.5 스파크플라즈마 소결법(Spark plasma sintering) 30
3. 실험방법 34
3.1 Bi2Te3계 열전재료의 제조 34
3.2 밀도측정 40
3.3 상 및 미세구조의 분석 40
3.4 열전특성의 평가 42
3.4.1 Seebeck 계수의 측정 42
3.4.2 전기비저항의 측정 42
3.4.3 열전도도의 측정 43
4. 결과 및 고찰 47
4.1 비환원처리 Bi2Te3계 열전재료 47
4.1.1 비환원처리 Bi2Te3계 열전재료의 소결특성 47
4.1.2 비환원처리 Bi2Te3계 열전재료의 이방성 특성 54
4.1.3 비환원처리 Bi2Te3계 열전재료의 열전특성 58
4.2 Bi2Te3계 열전재료의 수소환원처리 효과 69
4.2.1 수소환원 처리에 의한 Bi2Te3계 열전재료의 소결특성 69
4.2.2 수소환원 처리에 의한 Bi2Te3계 열전재료의 열전특성 74
5. 결론 80
Appendix 82
참고문헌 83
감사의 글 87
Table 1-1. The Temperature of usable Heat Source.6) 9
Table 3-1. The Composition of n- and p-Type Thermoelectric Materials. 36
Table 3-2. The Symbol of Specimens with the Control of Sintering. 38
Table 4-1. The Orientation Factor of n-Type Bi2Te2.7Se0.3 and p-Type Bi0.5Sb1.5Te3 Specimens made of non-reduced Powders, SPSed for 2 min as a Function of Sintering Condition 57
Fig. 1-1. The figure of merit of p-type and n-type hermoelectric materials with temperature.7) 10
Fig. 2-1. Thermoelectric effect. 14
Fig. 2-2. The principle of thermoelectric energy conversion. (a) thermoelectric generator, (b) refrigerator. 19
Fig. 2-3. Crystal structure of Bi2Te3 system.23) 22
Fig. 2-4. Phase diagram for (a) Bi2Te3-Sb2Te3 and (b) Bi2Te3-Bi2Se3 pseudo-binary system.24)～25) 23
Fig. 2-5. Schematic energy diagram for point defects in Bi2Te3. 25
Fig. 2-6. The relation between thermoelectric properties and carrier concentration.31) 27
Fig. 2-7. Current path ①, ② and ③ through graphite mold. 32
Fig. 2-8. Basic mechanism of neck formation by SPS; 33
Fig. 3-1. Schematic diagram of experimental procedures for the abrication of Bi2Te3-based thermoelectric materials. 35
Fig. 3-2. The particle size distribution of (a) n-type Bi2Te2.7Se0.3 and (b) p-type Bi0.5Sb1.5Te3 powdersball milled for 12 hr in ethyl alcohol under Ar atmosphere. 37
Fig. 3-3. The heating schedule of the specimens SPSedF, M and S represent fast, moderate and slow heating rate. 39
Fig. 3-4. Schematic diagram of the measurement surface for XRD and SEM. 41
Fig. 3-5. Schematic diagram of the apparatus for Seebeck coefficient measurement at 298K. 44
Fig. 3-6. Schematic diagram of electrical resistivity measurement. 45
Fig. 3-7. Schematic diagram of the apparatus for hermal conductivity measurement at 298K. 46
Fig. 4-1. SEM images of (a) n-type Bi2Te2.7Se0.3 and (b) p-typeBi0.5Sb1.5Te3 powders, which were not reduced and reduced by hydrogen gas after ball milling. 48
Fig. 4-2. The X-ray diffraction patterns of (a) n-type Bi2Te2.7Se0.3 and (b) p-type Bi0.5Sb1.5Te3, which were not reduced and reduced powders by hy- drogen gas after ball milling. 49
Fig. 4-3. Changes in the % theoritical density of n-type Bi2Te2.7Se0.3 and p-type Bi0.5Sb1.5Te3 specimens made of non-reduced powders, SPSed on the schedule M for 2 min as a function of sintering temperature. 50
Fig. 4-4. The SEM image of fracture surface of n-type Bi2Te2.7Se0.3 specimens made of non-reduced powders, SPSed on the schedule M for 2 min as a function of sintering temperature. 52
Fig. 4-5. The SEM image of fracture surface of p-type Bi0.5Sb1.5Te3 specimens made of non-reduced powders, SPSed on the schedule M for 2 min as a function of sintering temperature. 53
Fig. 4-6. The X-ray diffraction patterns of n-type Bi2Te2.7Se0.3 doped specimens made of non-reduced powders, SPSed on the schedule M for 2 min as a function of sintering temperature. 55
Fig. 4-7. The X-ray diffraction patterns of p-type Bi0.5Sb1.5Te3 specimens made of non-reduced powders, SPSed on the schedule M for 2 min as a function of sintering temperature. 56
Fig. 4-8. The Seebeck coefficient of n-type Bi2Te2.7Se0.3 and p-type Bi0.5Sb1.5Te3 specimens made of non-reduced powders, SPSed on the schedule M for 2 min as a function of sintering temperature. 59
Fig. 4-9. The Seebeck coefficient of n-type Bi2Te2.7Se0.3 and p-type Bi0.5Sb1.5Te3 specimens made of non-reduced powders, SPSed at 300oC for 2 min as a function of heating schedule. 61
Fig. 4-10. The electrical resistivity of n-type Bi2Te2.7Se0.3 and p-type Bi0.5Sb1.5Te3 specimens made of non-reduced powders, SPSed on the schedule M for 2 min as a function of sintering temperature. 62
Fig. 4-11. The electrical resistivity of n-type Bi2Te2.7Se0.3 andp-type Bi0.5Sb1.5Te3 specimens made of non-reduced powders, SPSed at 300oC for 2 min as a function of heating schedule. 64
Fig. 4-12. The thermal conductivity of n-type Bi2Te2.7Se0.3 and p-type Bi0.5Sb1.5Te3 specimens made of non-reduced powders, SPSed on the schedule M for 2 min as a function of sintering temperature. 65
Fig. 4-13. The thermal conductivity of n-type Bi2Te2.7Se0.3 and p-type Bi0.5Sb1.5Te3 specimens made of non-reduced powders, SPSed at 300oC for 2 min as a function of heating schedule. 67
Fig. 4-14. The figure of merit of n-type Bi2Te2.7Se0.3 and p-type Bi0.5Sb1.5Te3 specimens made of non-reduced powders, SPSed on the schedule M for 2 min as a function of sintering temperature. 68
Fig. 4-15. The figure of merit of n-type Bi2Te2.7Se0.3 and p-type Bi0.5Sb1.5Te3 specimens made of non-reduced powders, SPSed 300oC for 2 min as a function of heating schedule. 70
Fig. 4-16. The relative density of (a) n-type Bi2Te2.7Se0.3 and (a) p-type Bi0.5Sb1.5Te3 specimens made of non- reduced and reduced powders, SPSed on the schedu- le M for 2 min as a function of sintering tempera- ture. 71
Fig. 4-17. The SEM image of fracture surface for perpendicular to pressed direction(surface B) of n-type Bi2Te2.7Se0.3 specimens made of non-reduced and reduced powders, SPSed on the schedule M for 2 min as a function of sintering temperature. 72
Fig. 4-18. The SEM image of fracture surface for perpendicular to pressed direction(surface B) of p-type Bi0.5Sb1.5Te3 specimens made of non-reduced and reduced powders,SPSed on the schedule M for 2 min as a function of sintering temperature. 73
Fig. 4-19. The Seebeck coefficient of (a) n-type Bi2Te2.7Se0.3 and (b) p-type Bi0.5Sb1.5Te3 specimens made of non- reduced and reduced powders, SPSed on the schedu- e M for 2 min as a function of sintering temperature. 75
Fig. 4-20. The electrical resistivity of (a) n-type Bi2Te2.7Se0.3 and (b) p-type Bi0.5Sb1.5Te3 specimens made of non- reduced and reduced powders, SPSed on the schedu- e M for 2 min as a function of sintering temperature. 76
Fig. 4-21. The thermal conductivity of (a) n-type Bi2Te2.7Se0.3 and (b) p-type Bi0.5Sb1.5Te3 specimens made of non- reduced and reduced powders, SPSed on the schedu- le M for 2 min as a function of sintering temperature. 77
Fig. 4-22. The figure of merit of (a) n-type Bi2Te2.7Se0.3 and (a) p-type Bi0.5Sb1.5Te3 specimens made of non-reduced and reduced powders, SPSed on the schedule M for 2 min as a function of sintering temperature. 79
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