碲化鍺(GeTe)為現今中高溫型熱電材料中的發展主流，其優異的熱電傳輸性質和特殊的晶體結構吸引了許多研究團隊的目光。高熵工程(Entropy engineering)為一具有高度潛能改善熱電材料性質的手法，除了能同時提升熱電功率因子並降低晶格熱導率外，還能有助於材料結構的簡化。本研究以碲化鍺材料為出發，並加入熱電特性與其具有高度互補性之單硫化物(Monochalcogenides)的主要元素硫以及硒，再搭配其他元素製備出三個組成不同的(Ge/Sb/Ag/Sn)(S/Se/Te)新型高熵熱電材料，分別稱之為GSSST-Agx% (x = 0, 1, 4, 6)、GSSST-2 和GASST。首先，GSSST-Agx% (x = 0, 1, 4, 6)成功的藉由高熵效應(HEA effect)的引入將熱導率下降至極具有競爭力的範圍，最低之熱導率表現為GSSST-Ag4%於673 K時僅有~0.65 W/m·K。同時，其Seebeck係數也因能帶簡併(Band degeneracy)而有大幅度的改善，於673 K時提升到261 μV/K左右。接著，第二個系統GSSST-2則藉由控制其中GeS相的晶體取向(Crystallographic orientation)，將導電率提升了接近一個數量級，從原先GSSST-Agx%之~30 S/cm上升至110 S/cm左右。最後，本研究設計並製備出了晶體結構為單一相的的高熵熱電系統GASST，不同於前兩個系統的(GeTe/GeS)雙相結構，其展現了極佳的導電率，於30 – 400 C之溫度區間內皆保持在2000 S/cm左右，為一顯著的熱電優勢。

GeTe is an attractive material of high tunability in electrical/thermal transport properties. Thermoelectric property of GeTe-based compounds can be greatly improved with reducd thermal conductivity and enhanced power factor through a multielement alloying approach. In this work, we synthesized GeTe-based high-entropy alloys (HEAs) with notable (S, Se) substitution at Te sites and (Ag, Sb, Sn) at Ge sites by powder metallurgy. The influence of lattice distortion on phase transformation and transport properties was investigated. Three HEA thermoelectrics with different compositions were synthesized and designated as GSSST-Agx% (x = 0, 1, 4, 6), GSSST-2 and GASST respectively. The GSSST-Ag4% exhibits an extremely low thermal conductivity of 0.65 W/m·K by HEA effect at 673 K. Simutaneously, a highly improved Seebeck coefficient of ~261 μV/K is also achieved by band degeneracy. Next, The GSSST-2 has a modified element composition, which enhances the electrical conductivity from 30 S/cm to 110 S/cm over the whole temperature range. The promotion was attributed to the increased mobility by controlling the crystallographic orientation of GeS phase in the GSSST-2. The GeS (200) texture was beneficial to enhance the electrical mobility of the GSSST-2 sample. Herein, the mobility of GSSST-2 was 17 cm2/V⋅s compared to that of GSSST (6.4 cm2 /V⋅s). Finally, GASST, the third derivative of GSSST, was synthesized, which revealed a GeTe single phase rather than GeTe/GeS two-phase mixture. The GASST shows a competitive electrical conductivity of ~2000 S/cm over a temperature range of 30 – 400 C.

壹、 緒論 11
1.1研究背景 11
1.2研究動機 14
貳、 文獻回顧 16
2.1 高熵工程於熱電領域之應用 17
2.1.1 高熵合金定義 17
2.1.2 高熵合金之四大效應於熱電材料結構與性質的影響 18
2.1.3 高熵熱電材料之回顧 20
2.2 碲化鍺之基本性質 23
2.2.1 碲化鍺之晶體結構 23
2.2.2 碲化鍺之能帶結構 24
2.2.3 碲化鍺之晶體缺陷 27
2.2.4 碲化鍺之材料劣勢 28
2.3 二維單硫化物之基本性質 29
2.3.1 二維單硫化物之晶體結構 30
2.3.2 二維單硫化物之熱導性與Seebeck係數 31
2.3.3 二維單硫化物之材料劣勢 33
2.3.4 二維單硫化物之商用價值 35
參、 實驗步驟與分析方法 38
3.1 試片製備 39
3.2分析與量測方法 40
3.2.1 Seebeck係數與導電率之量測 40
3.2.2 霍爾量測(Hall measurement) 41
3.2.3 熱傳導係數量測 43
3.2.4 微結構、析出物及成分分析 44
3.2.5 X光繞射及Rietveld Refinement分析 44
3.2.6 熱重分析儀(Thermogravimetric analysis) 45
肆、 結果與討論 46
4.1 高熵熱電合金GSSST-Agx%之微結構、晶體結構與熱電性質分析 46
4.1.1 高熵熱電合金GSSST-Agx%之微結構 48
4.1.2 高熵熱電合金GSSST-Agx%之晶體結構 53
4.1.3 高熵熱電合金GSSST-Agx%之熱電性質 55
4.2 高熵熱電合金GSSST-2之微結構、晶體結構與熱電性質分析 59
4.2.1 高熵熱電合金GSSST-2之微結構 60
4.2.2 高熵熱電合金GSSST-2之晶體結構 61
4.2.3 高熵熱電合金GSSST-2之熱電性質 64
4.2.4 Ag摻雜對於高熵熱電合金GSSST-2之影響 68
4.3 高熵熱電合金GASST之微結構、晶體結構與熱電性質分析 73
4.3.1 高熵熱電合金GASST之微結構 74
4.3.2 高熵熱電合金GASST之晶體結構 76
4.3.3 高熵熱電合金GASST之熱電性質 77
伍、 結論 82
陸、 參考文獻 83

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