Bi2Te3化合物是室溫下熱電性質最突出的熱電材料，此類合金具有特殊的層狀結構以及非等向熱電特性，雖然對於單晶型的熱電塊材，特定晶軸方向具備較佳熱電特性，但是容易脆裂的缺點，將提高熱電材料機械加工的難度。而多晶型熱電材料則具有較佳之機械切削特性。本研究想要對於多晶型熱電材料的微結構與熱電特性做一系列的研究，使用粉末冶金製程，將熔煉塊材粉碎至不同粉末粒徑之粉末，利用單軸冷壓機製成塊材，並在不同溫度進行燒結處理，探討不同粉末粒徑與真空燒結溫度，對此類型熱電材料特性的影響，並針對內部微結構及缺陷與粉末粒徑及燒結溫度間變化的關係進行探討。結果顯示粒徑25μm的粉末在375℃燒結三小時後，可得最佳熱電優值約為0.92。另外在本實驗中發現，當燒結溫度超過碲元素熔點時，試片將會產生變形而無法使用，因此本研究嘗試進行表面改質，於粉末表面鍍錫，期望能與多餘的碲反應，避免試片變形。實驗結果發現，經過鍍錫後的熱電塊材，由於形成高熔點的SnTe相，確實避免低熔點的Te相熔融所發生的變形現象。然而，鍍錫處理將提高材料的電阻率與熱傳導係數，因此，粉末經過鍍錫處理的燒結塊材，其熱電優值，降低至0.3以下，本研究亦將針對表面粉末改質對其熱電材料特性之影響，進行探討。

Bi2Te3 compound, known for its special layered structure and anisotropic thermoelectric properties, is the best thermoelectric material for room temperature applications. Single crystalline Bi-Te materials own superior thermoelectric properties along specific crystal orientation, but their brittleness raises difficulty in machining thermoelectric elements. On the other hand, polycrystalline Bi-Te materials have better cutting and machining characteristics than Bi-Te single crystals. In this study we prepared Bi0.5Sb1.5Te3 powders from a pre-melted Bi0.5Sb1.5Te3 compound using ball milling method. These powders were cold-pressed at 600 MPa and then sintered at temperature ranging from 300~450℃ for 3 hrs. The effects of powder size and sintering temperature on the microstructure, thermoelectric properties and defects of the sintered Bi0.5Sb1.5Te3 materials were investigated. It is suggested that a highest figure-of-merit value of 0.92 was achieved for the compacted alloy prepared by 25μm powders and sintered at 375℃ for 3 hrs. It is also found that the sintered specimen would deform badly when the sintered temperature is above 421 ºC, the melting point of tellurium. By coating a thin Sn layer on the powder surface, the reaction between Sn and excess Te leads to the formation of SnTe compound that can resolve the specimen deformation problem. However, the Sn coating treatment results in a large increase in both electrical resisitivity and thermal conductivity of the sintered alloy- and in turn a low ZT value of 0.3 at 300K. The effects of Sn coating treatment on the thermoelectric properties of the sintered alloy are also discussed.

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