보고서 정보
주관연구기관 |
대구경북과학기술원 Daegu Gyeongbuk Institute of Science and Technology |
보고서유형 | 연차보고서 |
발행국가 | 대한민국 |
언어 |
한국어
|
발행년월 | 2013-12 |
과제시작연도 |
2013 |
주관부처 |
미래창조과학부 Ministry of Science, ICT and Future Planning |
등록번호 |
TRKO201500002250 |
과제고유번호 |
1711008660 |
사업명 |
대구경북과학기술원연구운영비지원(0.5) |
DB 구축일자 |
2015-05-16
|
키워드 |
열전.열전소재.결정배향.모듈.변환효율.나노기술.열전성능지수.전기전도도.제벡계수.열전도도.Thermoelectrics.Thermoelectric material.Crystal alignment.Module.Power conversion efficiency.Nanotechnology.Figure of merit.Electrical conductivity.Seebeck coefficient.Thermal conductivity.
|
DOI |
https://doi.org/10.23000/TRKO201500002250 |
초록
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1. 열전소재 제조 기술(나노벌크 및 신물질 제조 기술 개발)
- 중저온용 BiTe계 나노열전소재: ZT≥1.0@300~423 K
- 신규 열전소재 발굴: 저온용 I-III-VI계 열전소재 합성, 물성 측정 및 scale-up
(≥30g/batch)
2. 열전소재 가공 기술(결정방향 제어 및 소결기술 개발)
- 열전소재의 결정방향 제어(10T 초전도 자석 이용) → 결정방향 일치도 60% 수준 확보
- 결정배향체 소결기술 개발 및 열전특성 측정
3. 열전소자 제조 기술(열전모듈 설계, 제조 기술
1. 열전소재 제조 기술(나노벌크 및 신물질 제조 기술 개발)
- 중저온용 BiTe계 나노열전소재: ZT≥1.0@300~423 K
- 신규 열전소재 발굴: 저온용 I-III-VI계 열전소재 합성, 물성 측정 및 scale-up
(≥30g/batch)
2. 열전소재 가공 기술(결정방향 제어 및 소결기술 개발)
- 열전소재의 결정방향 제어(10T 초전도 자석 이용) → 결정방향 일치도 60% 수준 확보
- 결정배향체 소결기술 개발 및 열전특성 측정
3. 열전소자 제조 기술(열전모듈 설계, 제조 기술 개발)
- 64-chip 모듈용 기판 및 소결체 크기 설계
- 접합부(전극, 소결체, 확산방지층) 설계 및 제조
- 64-chip 모듈성능 평가(ZTmodule ≥ 0.7 ZTmaterial)
Abstract
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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].
With the meteoric development in nanotechnology, many groups have been trying to build low-dimensional structures to use as a type of PGEC material. Reports have shown that ZT can be enhanced in quantum dots (QD) and superlattice (SL) thin films both because of the increase in the power factor (α2σ) and the decrease in κ, which result from quantum confinement and the phonon scattering effect, respectively [13-21]. Relatively high ZT values are often exhibited in these QDs or SL structures, but the commercial use of these substances is difficult because of complicated production processes and high costs. Therefore, some groups have focused on using nanobulk structures, such as nanoparticles [22-24], nanotubes [25-27], and nanowires [28-30]. Not only do these nanostructures still exhibit the phonon scattering effect, which reduces κ, but they can also be prepared by cheaper methods.
TE materials are usually classified according to the temperatures at which they are operated. For low-temperature operations (0 to 250 ℃), Bi2Te3-type semiconductors have primarily been investigated because of their favorable ZT value in this temperature range. The p-type semiconductor, bismuth antimony telluride (BixSb2-xTe3), has a high α2σ, resulting in an excellent ZT value (normally about 1.0 at 50 to 150 ℃) [14,31-33].
In addition, some research groups have endeavored to fabricate nanobulk Bi0.5Sb1.5Te3 to reduce κ [34-38]. Thus, the highest ZT value, 1.4 at 100 ℃ 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 (Bi2TeySe3-y), are relatively rare, likely because of their low ZT values. In addition, the study of a Bi2TeySe3-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 adjust some of the parameters of the preparation process, which caused large variations in the carrier density, the electrical resistivity, and the Seebeck coefficient. The whole process was optimized by choosing the predominant physical and transport properties.
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 MnSi2-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.
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