PbTe合金為典型的中溫型熱電材料，適用於一般工業廢熱回收，操作溫度範圍約為500~800K，一般而言提高熱電優值主要有兩個方向：(1)藉由增加材料載子濃度而提升熱電功率因子(power factor)，(2)藉由增加材料內部聲子(phonon)散射來降低其熱傳導係數，且不會降低太多導電率。國際間採用加入不同添加物或不同融煉熱壓的製程來提升熱電優值，但遇到再現性不佳的瓶頸。
而本實驗利用方向性凝固方法製備AgPb18SbTe20熱電材料，藉由給予一溫度梯度，來控制其合金凝固時材料的組成與析出等現象，且配合微觀結構與成份分析進而對材料熱電特性來做探討。一開始利用四種元素粉末 (Ag, Pb, Te, Sb) 在真空下進行熔煉，並且以Ag熔點溫度960℃為界來討論熔煉溫度970℃與920℃的差異，然後搭配不同載台下降速率做為對照，最後與先熔煉得到Pb18Te20合金再添加Ag、Sb元素粉末進行熔煉的鑄件來進行比較分析。

Lead telluride (PbTe) is one of the typical materials used in the construction of thermoelectric generators working in the intermediate temperature range (500-800K). In this temperature scope, the materials are applied to recycling exhausted heat in industry. In the literature, many efforts are made to increase figure of merit (ZT) including increasing carrier concentration to enhance thermoelectric power factor and using scattering effect of phonon to decrease thermal conductivity. With these efforts, many studies discuss adding different element as dapant to control the electrical conductivity or applying different melting methods and hot pressing processes to enhance figure of merit. However, the poor reproducibility bottlenecks are encountered in these researches.
In this study, the thermoelectric material AgPb18SbTe20 is made by using a directional solidification method. With the scheme, to control the solidified composition, precipitate structure and so on by employing a temperature gradient is the key point to investigate the thermoelectric properties of the manufactured materials with the different resulting microstructures. In beginning of the study, elemental powders (Ag, Pb, Te, Sb) are weighted, melted and then solidified in a sealed quartz tube under the vacuum condition. Different melting temperatures 920 and 970 degree Celsius with different descending platform rates are utilized in this research. Besides, the powders of the pre-made Pb18Te20 alloy mixed with the ones of Ag and Sb are also used to manufacture the thermoelectric materials. Finally, the thermoelectric properties of the materials made in the different ways are compared and analyzed.

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