초록 ▼

1. 열전소재 분야 연구결과
- 적용온도별 특화형 열전소재 제조 기술
· 상온용 열전소재 :
- 상용 Bi-Te계 열전소재의 대량 제조공정 확보 및 소재성능 round robin test 완료
(n-type : ZT≃0.91, p-type : ZT≃1.12)
- 나노기반 Bi-Te계 대량 제조공정 확보
- Bi-Te/polymer hybrid 소재 개발 (ZT≃0.6@RT~150˚C)

· 중온용 열전소재 :
- Zn4Sb3, ZnSb. W-Se, Mg2Si, SnSe 소재 제조기술

1. 열전소재 분야 연구결과
- 적용온도별 특화형 열전소재 제조 기술
· 상온용 열전소재 :
- 상용 Bi-Te계 열전소재의 대량 제조공정 확보 및 소재성능 round robin test 완료
(n-type : ZT≃0.91, p-type : ZT≃1.12)
- 나노기반 Bi-Te계 대량 제조공정 확보
- Bi-Te/polymer hybrid 소재 개발 (ZT≃0.6@RT~150˚C)

· 중온용 열전소재 :
- Zn4Sb3, ZnSb. W-Se, Mg2Si, SnSe 소재 제조기술 개발
(Zn4Sb3 : ZT≃1.35@400˚C)
- Bi/CNT doped ZnSb 소재 제조기술 개발

2. 열전소자 제조분야 연구결과
- 10T 자기장을 이용한 결정방향 제어공정 확보
- 245chip Bi-Te계 열전소자 제조기술 확보
- 1chip Mg2Si 소자 제조공정 확보

3. 열전시스템 분야 연구결과
- 냉온수 열전발전시스템 설계 및 시제품 개발

4. 열전소재/소자 평가기술 분야 연구결과
- 열전소재/소자 round robin test 실시
- 열전소자 특성평가장치 제작

( 출처 : 보고서 초록 3p )

Abstract ▼

Thermoelectric (TE) materials have been intensively researched because of their attractive applications, such as waste heat-to-electricity conversion and solid-state cooling [1-7]. In this field, one of the main topics of research has been the improvement of the performance of TE materials(n- and p-

Thermoelectric (TE) materials have been intensively researched because of their attractive applications, such as waste heat-to-electricity conversion and solid-state cooling [1-7]. In this field, one of the main topics of research has been the improvement of the performance of TE materials(n- and p-type semiconductors) to increase the efficiency of TE devices. The comprehensive performance of such materials is evaluated via the dimensionless figure of merit ZT=α²σT/κ, where α is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature, and κ is the thermal conductivity [5-10]. Therefore, an excellent TE material should have both a high σ and a low κ,characteristics indicative of a so-called phonon-glass/electron-crystal (PGEC) [1,7,8-15]. A variety of high ZT materials have been developed and many thermoelectric materials have an upper temperature limit of operation, above which the materials unstable.
Therefore, no single material is best for all temperature ranges, so different materials should be selected for different applications based on the temperature operation.

TE materials are usually classified according to the temperatures at which they are operated. For low-temperature operations (0 to 250 °C), Bi₂Te₃-type semiconductors have primarily been investigated because of their favorable ZT value in this temperature range. The p-type semiconductor, bismuth antimony telluride (Bi_xSb_2-xTe₃), has a high α² σ, resulting in an excellent ZT value (normally about 1.0 at 50 to 150 °C) [14,31-33].
In addition, some research groups have endeavored to fabricate nanobulk Bi_0.5Sb_1.5Te₃ to reduce κ [34-38]. Thus, the highest ZT value, 1.4 at 100 °C has been achieved with this material [24]. P-type semiconductors have been actively investigated, but research into the n-type semiconductors, bismuth telluride (Bi₂Te₃) or bismuth tellurium selenide(Bi₂Te_ySe_3-y), are relatively rare, likely because of their low ZT values. In addition, the study of a Bi₂Te_ySe_3-y nanocompound for κ reduction has never been done, to the best of our knowledge. Therefore, we intended to synthesize the binary and ternary nanocompounds via a brief chemical synthetic route and to examine the effect of their nanostructure on κ. Moreover, we attempted to scale-up the preparation process for the commercialization and thermoelectric module fabrication. Unignorable variations in transport properties such as carrier density, electrical resistivity, Seebeck coefficient, and thermal conductivity were detected after the scale-up; thus, we tried to optimize the process by choosing predominant physical and transport properties. We also fabricated the hybrid thermoelectric materials between Bi2Te3 and conjugated polymers. Conjugated polymers can have narrow bandgap because of their π-bond, and thus they can be used as conducing substances. In addition, they basically show low thermal conductivity, therefore they are recognized as typical phonon glass electron crystal (PGEC) materials. It is why we attempted to hybridize them with Bi2Te3.

For mid-temperature operations (0 to 250 °C), we preferentially chose some candidates such as Zn4Sb3 and WSe2 because they are relatively inexpensive and harmless. It is generally known that n-type Zn4Sb3 has not been reported, and thus we attempted to adopt n-type characteristic via theoretical physical analyses followed by empirical fabrication and observation. Meanwhile, we successfully prepared WSe2 via a solid-state reaction and found its p-type property and low electrical conductivity. We lately tried to increase its carrier concentration by employing appropriate dopants.

In polymeric and ceramic materials of paramagnetism and/or diamagnetism with magnetic anisotropy, highly textured microstructures have been fabricated by colloidal processing under strong magnetic field followed by appropriate heat and/or mechanical treatments. The textured microstructure improved physical and mechanical properties [39,40]. Several thermoelectric materials like MnSi_2-x [41], aluminum doped ZnO [42], and calcium–cobalt oxide [43] have been investigated with the above magnetic texturing method. Their results showed a possibility to reduce the electrical resistivity owing to the uni-directionally aligned crystals. Bi–Te compounds possess a layered hexagonal structure comprised of five atom stacks of Te–Bi–Te–Bi–Te, and the Te–Te layers are bonded by a weak van der Waals force. It is well known that these materials have thermoelectric anisotropy originated from this structural anisotropy [44]. Delves and co-workers first reported on the anisotropy of the electrical resistivity with single crystalline Bi₂Te₃ between along van der Waals boding plane and along the direction perpendicular to the bonding plane [45]. Their experimental measurements indicated that the electrical resistivity along the van der Waals bonding plane was smaller than that along the direction perpendicular to the bonding plane. These observations on the single crystalline BiTe system reveal a possibility that electrical conductivity can be enhanced by adjusting the crystal orientation of grains in polycrystalline BiTe materials. Hence, we endeavored to apply high magnetic field to the fabricated BiTe materials for improving electrical conductivity.

Based on the above the literature surveys and the experimental trials, we propose a hypothesis to improve thermoelectric performance such that nanostructures with uni-directionally aligned crystals may enjoy both lowering thermal conductivity coming from nanostructure and increasing electrical conductivity from crystal alignment.
Namely, Wiedemann–Franz relationship can be overcome and this results in the improvement of thermoelectric performance.

Before we fabricate thermoelectric devices (modules), we predicted the performance of modules by considering physical variables in modules such as temperature, heat flux, and contact resistance. Based on the results of the physical analysis, we designed thermoelectric modules. Preferentially, we adopted commercial thermoelectric materials prepared by a conventional melting process to fabricate the modules. When we stabilize the fabricating technology of the modules, the crystal-aligned thermoelectric nanomaterials will be adopted.

( 출처 : SUMMARY 12p )

목차 Contents

• 표지 ... 1
• 제 출 문 ... 2
• 보고서 초록 ... 3
• 요 약 문 ... 4
• S U M M A R Y ... 12
• C O N T E N T S ... 15
• 목차 ... 16
• 제 1 장 연구개발과제의 개요 ... 17
• 제 1 절 연구개발 목적 및 필요성 ... 17
• 1. 기술적 측면 ... 17
• 2. 경제·산업적 측면 ... 19
• 제 2 절 연구개발 범위 ... 21
• 1. 연구개발의 최종목표 ... 21
• 2. 연구개발의 성격 및 내용 ... 21
• 제 2 장 국내외 기술개발 현황 ... 22
• 제 1 절 국내외 기술개발 현황 ... 22
• 제 2 절 현보유 기술대비 국내외 기술개발 현황 비교 ... 25
• 제 3 장 연구개발 수행내용 및 결과 ... 29
• 제 1 절 연구개발 수행내용 및 연구결과 ... 29
• 1. 열전소재 제조기술 ... 29
• 2. 열전소자 제조기술 ... 50
• 3. 열전시스템 개발 ... 55
• 4. 열전소재/소자 평가기술 개발 ... 55
• 제 2 절 대표연구실적 사례 ... 60
• 제 4 장 목표달성도 및 관련분야에의 기여도 ... 61
• 제 1 절 목표 달성도 ... 61
• 제 2 절 관련분야에의 기여도 ... 66
• 제 5 장 연구개발결과의 활용계획 ... 67
• 제 1 절 활용계획 ... 67
• 제 2 절 기대효과 ... 67
• 제 6 장 차년도 연구계획 ... 69
• 제 1 절 국내외 관련분야의 환경변화 ... 69
• 제 7 장 연구개발과정에서 수집한 해외과학기술 정보 ... 70
• 제 8 장 참고문헌 ... 86
• 끝페이지 ... 89