p型BiSbTe與n型Bi2Te3-CuSe熱電材料及其模組之製備與熱電性能評估

Abstract

本研究以p型BiSbTe與n型Bi2Te3-CuSe熱電材料為主軸，透過熔融甩帶製程（melt spinning）結合放電電漿燒結（spark plasma sintering, SPS）製備塊材熱電材料，並進一步組裝為PN熱電模組，以系統性評估其相結構、微觀形貌、表面化學狀態、熱電性質與模組輸出性能。 在p型材料方面，本研究以Bi0.5Sb1.5Te3-X為基材，探討Te含量調控與SiO2奈米粒子添加對BiSbTe熱電性能之影響。XRD分析結果顯示，樣品經球磨、退火、melt spinning與SPS製程後，仍維持BiSbTe主要晶相，且SiO2添加並未明顯破壞基材之晶體結構。SEM、EDS、STEM-EDS與HRTEM分析結果顯示，SiO2奈米粒子可分散於BiSbTe基材中，並於晶界或基材內部形成奈米尺度異質界面，提供額外聲子散射中心。進一步由XPS分析可確認BST-SiO2複合材料中Bi、Sb、Te 主要與BiSbTe基體鍵結相關，而Si 2p與O 1s訊號則可佐證SiO2奈米粒子之存在。熱電性質量測結果顯示，適量SiO2添加可在維持電性傳輸特性的同時有效降低熱導率，其中BST-2vol.% SiO2樣品展現最佳熱電性能，其ZT值於360-400K附近可達約1.52。 在n型材料方面，本研究以Bi2Te3-CuSe複合材料為研究對象，探討melt spinning與後退火處理對其相結構、微結構與熱電性質之影響。XRD分析結果顯示，Bi2Te3為主要晶相，並可觀察到CuSe相關特徵峰，證實CuSe第二相成功導入Bi2Te3基材中。SEM/EDS 分析結果顯示，甩帶後樣品於接觸面、自由面與橫截面皆具有良好的元素分布均勻性，顯示快速凝固製程有助於降低大尺度元素偏析。進一步經後退火處理後，HRTEM與FFT分析顯示樣品中可形成Bi2Se3-like nanodots。此類奈米析出相與CuSe第二相可於Bi2Te3基體中提供額外異質界面，進一步增強聲子散射，並有助於改善Bi2Te3-CuSe複合材料之熱電性能。 最後，本研究將自製p-type BST與n-type Bi2Te3-CuSe熱電腳組裝成PN熱電模組，並利用Al2O3陶瓷基板、Cu電極、Ni foil擴散阻障層與In-Sn solder建立電性串聯與熱性並聯之模組結構。模組量測結果顯示，開路電壓隨冷熱端溫差增加而近似線性上升，證實p-type與n-type熱電腳已形成有效之電性連接。I-V與P-I曲線分析進一步顯示，模組最大輸出功率隨溫差增加而明顯提升；當ΔT=120K時，最大輸出功率可達約10.84mW，為本研究量測範圍內之最高值。進一步根據一維穩態熱傳模型估算，模組於ΔT=120K時之輸入熱量約為0.405W，對應轉換效率約為2.7%。整體而言，本研究成功建立由材料製備、微結構與表面化學態分析、熱電性能量測至模組輸出與效率評估之完整研究架構，並證實自製p型BiSbTe與n型Bi2Te3-CuSe材料具有應用於低溫至中溫熱電發電模組之潛力。

This study investigates the synthesis, thermoelectric performance, and module integration of p-type BiSbTe and n-type Bi2Te3-CuSe materials. Dense bulk samples were fabricated using melt spinning combined with spark plasma sintering, followed by systematic characterization of their phase structures, microstructures, surface chemical states, thermoelectric properties, and module-level performance. For the p-type materials, Bi0.5Sb1.5Te3-X was used as the matrix to examine the effects of Te content and SiO2 nanoparticle addition. XRD results confirmed that the BiSbTe phase was retained throughout processing, while microscopic analyses revealed dispersed SiO2 nanoparticles and nanoscale heterogeneous interfaces that enhanced phonon scattering. XPS further verified the presence of SiO2 and the bonding states of Bi, Sb, and Te. An appropriate SiO2 content reduced thermal conductivity without severely degrading electrical transport. The BST-2 vol.% SiO2 sample exhibited the highest performance, reaching a maximum ZT of approximately 1.52 at 360-400 K. For the n-type materials, the effects of melt spinning and post-annealing on Bi2Te3-CuSe composites were investigated. XRD confirmed Bi2Te3 as the main phase with CuSe as a secondary phase. SEM/EDS analyses showed relatively uniform elemental distributions, indicating that rapid solidification effectively suppressed large-scale segregation. After post-annealing, Bi2Se3-like nanodots were observed by HRTEM and FFT. These nanodots and CuSe-related heterogeneous interfaces enhanced phonon scattering and improved thermoelectric performance. A PN thermoelectric module was subsequently assembled using the synthesized p-type and n-type legs. The module consisted of Al2O3 substrates, Cu electrodes, Ni diffusion barriers, and In-Sn solder, with the thermoelectric legs connected electrically in series and thermally in parallel. The open-circuit voltage increased nearly linearly with temperature difference, while the maximum output power increased significantly. At ΔT = 120 K, the module achieved a maximum output power of approximately 10.84 mW. A one-dimensional steady-state heat-transfer model estimated a heat input of approximately 0.405 W, corresponding to a conversion efficiency of approximately 2.7%. Overall, this study establishes a complete framework from thermoelectric material synthesis and characterization to module fabrication and performance evaluation, demonstrating the potential of BiSbTe and Bi2Te3-CuSe materials for low- to medium-temperature power-generation applications.