具反蛋白石結構之碲化鉍電鍍膜層微結構與熱電性質研究

Microstructure and thermoelectric properties of electrodeposited Bi2Te3 films with inverse opal structure

楊孟璇(Meng-Hsuan Yang)

指導教授 ： 廖建能

國立清華大學/工學院/材料科學工程學系/碩士(2014年)

摘要

熱電材料是一種可將熱能與電能進行相互轉換的綠色材料，碲化鉍(Bi2Te3)化合物是在室溫應用範圍具最佳熱電優值的材料。本研究採用定電流模式(2.5 mA/cm2)電鍍製備三種不同孔徑尺寸的反蛋白石結構(直徑分別約為300 nm (PS-300)、400 nm (PS-400)和600 nm (PS-600)及無孔洞的完整碲化鉍膜層，由於反蛋白石結構具有以最密堆積方式排列的規則孔洞，可明確推知孔洞的數量及面積，因此可對此類型膜層的結構與性質做有系統的分析及探討。本研究探討退火製程對於不同孔徑尺寸的反蛋白石結構膜層間晶體微結構與熱電性質之影響，並與完整膜層互相比較。X光繞射實驗結果顯示，所有試片皆具有(110)優選方向，並在退火製程初期發生消除空位缺陷的回復過程導致(110)方向結晶性成長。而延長退火時間將發生再結晶行為，膜層(110)方向的繞射峰強度開始減弱，其他方向的繞射峰強度則開始變大。推測在退火製程中，反蛋白石結構膜層由於鉍原子含量比例較多，富鉍相的析出與晶格內部形成錯位缺陷的兩種機制將因微結構的差異而相互競爭，因此擁有單位體積孔洞數量最少與界面總面積最小的PS-600試片，在退火過程中空位缺陷消除的幅度最大。此外，由於反蛋白石結構膜層內部大量的孔洞與界面薄區限制晶粒的成長及載子傳輸路徑，導致退火過的試片其載子遷移率無法如完整碲化鉍膜層大幅提升而有較高的電阻率。然而，反蛋白石結構碲化鉍膜層較佳的晶體結構與載子散射界面將呈現較高的Seebeck係數。

關鍵字

反蛋白石結構 ； 碲化鉍 ； 熱電 ； 電鍍

並列摘要

Thermoelectric material, that can convert thermal energy into electrical energy and vice versa, is one potential candidate of green materials. Bismuth telluride based compounds have superior thermoelectric figure of merit at room temperature regime. In this research, Bi2Te3 thin film with inverse opal structure that have three different pore sizes (PS-300 ( = 300 nm), PS-400 ( = 400 nm), and PS-600 ( = 600 nm)) as well as dense Bi2Te3 films were prepared by electrodeposition under a fixed current density of 2.5 mA/cm2. Owing to ordered pore arrangement (closed packing), a systematic study of structure and thermoelectric properties of Bi2Te3 films with the inverse opal structure can be conducted. The aim of this research is to investigate the influence of annealing process on crystallographic microstructure and thermoelectric properties of Bi2Te3 film with different pore sizes, and compare it with the results of dense Bi2Te3 films. The x-ray diffraction results reveal that all the as-deposited specimens have (110) preferred orientation. The intensity of (110) reflection increases with annealing in the early stage due to elimination of vacancies. With extended annealing time, the intensity of (110) reflection decreases while those of other reflections increases due to recrystallization process in the Bi2Te3 films. It is speculated that precipitation of Bi-rich phase and formation of p-type antisite defects compete with each other in the inverse opal structure with different pore size during annealing process. The PS-600 specimen has the smallest number of pores and the best crystallinity, resulting in the largest amount of vacancies eliminated during thermal annealing. Owing to the large number of pores and the thin walls between the pores restrict grain growth and transport of charge carriers, the annealed Bi2Te3 films with inverse opal structure have smaller mobility and in turn higher electrical resistivity than the dense Bi2Te3 films. However, the Bi2Te3 films with inverse opal structure show an enlarged Seebeck coefficient caused by good crystallinity and abundant scattering interfaces.

並列關鍵字

inverse opal structure ； bismuth telluride ； thermoelectric ； electrodeposition

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