Bi-Sb-Se-Te 熱電材料系統相圖

Bi-Sb-Se-Te四元系統有相當好的熱電應用，Bi2Te3、Sb2Te3等材料已於商業上使用一段時間，研究指出當Bi2Te3、Sb2Te3參雜Se能有效地提升熱電性質。相圖能提供相平衡資訊，是相當重要的基礎知識，我們可以透過實驗方法或是Calphad計算來得到相圖。本研究將以實驗方法來建構Bi-Sb-Se-Te及其相關子系統的相圖。此四元系統有六個二元子系統，分別為Bi-Sb, Bi-Se, Bi-Te, Sb-Se, Sb-Te 和Se-Te，以及四個三元子系統，Bi-Sb-Se, Bi-Sb-Te, Bi-Se-Te 和 Sb-Se-Te.。六個二元子系統資料將從文獻中獲得，Sb-Se-Te的三元系統相圖已有資料，本研究將根據文獻中可使用的二元相圖，以及實驗結果來建構出餘下的三個三元系統相圖。探討的溫度選定250℃及400℃。本研究以純元素鉍、銻、硒、碲配置不同組成比例的三元Bi-Sb-Se、Bi-Sb-Te、Bi-Se-Te與Sb-Se-Te合金，並以SEM(Scanning Electron Microscopy)、EPMA(Electron Probe Microanalysis)與XRD(X-ray Diffraction)進行樣品的微結構分析、組成分析與相鑑定。根據所得到的實驗結果，以及二元系統相圖邊界，來建構出三元系統的相圖。 Bi-Sb-Se三元系統液相線投影圖中，Bi-Sb二元系統為完全互溶，邊界上沒有二元相；Sb-Se二元系統邊界上有一Sb2Se3二元相；Bi-Se二元系統中有一Bi2Se3二元相，以及一系列複雜的介金屬相，統合為(Bi2)m(Bi2Se3)n相。實驗結果並沒有發現三元相的出現。此系統有四個首要析出區，分別為Bi2Se3、Sb2Se3、(Bi2)m(Bi2Se3)n、(Bi,Sb)。 Bi-Sb-Se 400℃等溫橫截面圖中，發現一三元相Bi35Sb40Se25，此三元系統有六個tie-triangles，分別為Liquid+(Bi,Sb)+ Bi35Sb40Se25、Bi35Sb40Se25+Liquid+(Bi2)m(Bi2Se3)n、Bi35Sb40Se25+(Bi2)m(Bi2Se3)n +Sb2Se3、Bi2Se3+Sb2Se3+(Bi2)m(Bi2Se3)n 、 Sb2Se3+(Bi,Sb)+ Bi35Sb40Se25以及Bi2Se3+Sb2Se3+Liquid(Se)。 Bi-Sb-Te 400℃等溫橫截面相圖中，沒有發現三元相，有四個tie-triangles，分別為Liquid+(Bi,Sb)+ δ-(Sb2Te) 、Liquid+δ-(Sb2Te)+ (Bi2)m(Bi2Te3)n、δ-(Sb2Te)+ γ-(SbTe)+ (Bi2)m(Bi2Te3)n以及 (Bi2)m(Bi2Te3)n+ γ-(SbTe)+(Bi,Sb)2Te3。 Bi-Se-Te 400℃等溫橫截面相圖中，未發現三元相，在Bi-Se及Bi-Te二元系統中的複雜二元相群，簡化成Bi2Se3、(Bi2)m(Bi2Se3)n及Bi2Te3、(Bi2)m(Bi2Te3)n。而Bi2Se3與Bi2Te3在400℃會完全互溶成Bi2(Se,Te)3 相；(Bi2)m(Bi2Se3)n及(Bi2)m(Bi2Te3)n兩者在400℃ 完全互溶，生成(Bi2)m(Bi2(Se,Te)3)n 相。在400℃的Bi-Se-Te等溫橫截面圖，有Bi2(Se,Te)3+Liquid+(Se,Te)一個三相區。 Sb-Se-Te 250℃等溫橫截面圖中，沒有三元相的生成，此三元系統具有五個tie-triangles，分別為Sb2Se3+δ-Sb2Te+Sb、Sb2Te3+Sb2Se3+(Se,Te) 、 Sb2Se3+ δ-(Sb2Te)+ γ-(SbTe) 、 Sb2Se3+Sb2Te3+ γ-(SbTe) 以及Sb2Se3+Liquid+(Se,Te)。定40%Bi 400℃的Bi-Sb-Se-Te的等值剖面圖，目前已完成了(Bi2)m(Bi2(Se,Te)3)n 單相區及(Bi2)m(Bi2(Se,Te)3)n+Bi2(Se,Te)3兩相區。

關鍵字

Bi-Sb-Se-Te ；熱電材料；相圖；液相線投影圖

並列摘要

Bi-Sb-Se-Te quaternary system has high thermoelectric application interests. The materials Bi2Te3and Sb2Te3 are commercially utilized for a while. Literatures results have indicated that their thermoelectric properties could be improved with selenium doping Phase diagrams provide phase equilibria data which are fundamentally important. Phase diagrams can be determined by experimental measurements and by Calphad-type caBITLPulation. This study determine the phase diagrams of Bi-Sb-Se-Te and its constituent systems plans by experimental method. The quaternary system has six constituent binary systems, Bi-Sb, Bi-Se, Bi-Te, Sb-Se, Sb-Te and Se-Te and four constituent ternary systems, Bi-Sb-Se, Bi-Sb-Te, Bi-Se-Te and Sb-Se-Te. The phase diagrams of all the six constituent binary systems are adopted directly from those results which are available in the literatures with proper assessment. The phase diagram of Sb-Se-Te ternary system has been done. This study builds the other ternary system phase diagrams based on binary phase and experimental results. The examined temperature in this study is 250℃ and 400℃. This study uses Bi、Sb、Se and Te elements to prepare different atomic percentage ternary Bi-Sb-Se、Bi-Sb-Te、Bi-Se-Te and Sb-Se Te alloy. The microstructures, compositions, and diffraction peaks were determined using scanning electron microscopy(SEM), electron probe microanalysis(EPMA) and X-ray Diffraction(XRD). According to the experimental results and the boundaries of binary system phase diagrams determine ternary system phase diagrams. For Bi-Sb-Se liquidus projection, Bi-Sb system is isomorphous system without binary compound at the boundary. There is a line compound Sb2Se3 at the boundary of Sb-Se binary system. For Bi-Se binary system, there are a Bi2Se3 binary compound and a series of complicated binary compounds grouped as (Bi2)m(Bi2Se3)n. No ternary compound is found. There are four primary solidification phase regions, Bi2Se3, Sb2Se3 and, (Bi2)m(Bi2Se3)n and (Bi,Sb). Experimental results show that the 400℃ isothermal section of Bi-Sb-Se ternary system exists a ternary compound and 6 tie-triangles. The ternary compound is Bi35Sb40Se25 and the 6 tie-triangles are Liquid+(Bi,Sb)+ Bi35Sb40Se25, Bi35Sb40Se25+Liquid+(Bi2)m(Bi2Se3)n, Bi35Sb40Se25+(Bi2)m(Bi2Se3)n +Sb2Se3, Bi2Se3+Sb2Se3+(Bi2)m(Bi2Se3)n, Sb2Se3+(Bi,Sb)+ Bi35Sb40Se25 and Bi2Se3+Sb2Se3+Liquid. In the Bi-Sb-Te 400℃ isothermal section, no ternary compound is found. The phase diagram shows that there are 4 tie-triangles which are Liquid+(Bi,Sb)+ δ-(Sb2Te) 、Liquid+δ-(Sb2Te)+ (Bi2)m(Bi2Te3)n、δ-(Sb2Te)+ γ-(SbTe)+ (Bi2)m(Bi2Te3)n and (Bi2)m(Bi2Te3)n+ γ-(SbTe)+(Bi,Sb)2Te3 There is no ternary compound in the Bi-Se-Te ternary system at 400℃. The complicated binary phases in the Bi-Se and Bi-Te binary systems are grouped as Bi2Se3, (Bi2)m(Bi2Se3)n and Bi2Te3, (Bi2)m(Bi2Te3)n. The Bi2Se3 and Bi2Te3 form a solid solution Bi2(Se,Te)3 at 400℃. The (Bi2)m(Bi2Se3)n and (Bi2)m(Bi2Te3)n form a continuous solid solution (Bi2)m(Bi2(Se,Te)3)n. There is one tie-triangles which is Bi2(Se,Te)3+Liquid+(Se,Te). Experimental measurements are carried to determine the 250℃ isothermal section of Sb-Se-Te ternary system. No ternary compound is found. There are five tie-triangles, which are Sb2Se3+δ-Sb2Te+Sb, Sb2Te3+Sb2Se3+(Se,Te), Sb2Se3+ δ-(Sb2Te)+ γ-(SbTe), Sb2Se3+Sb2Te3+ γ-(SbTe), Sb2Se3+Liquid+(Se,Te) and Sb2Se3+ δ-(Sb2Te)+Sb, Sb_2 Te_3+Sb_2 Se_3 + (Se,Te) . For 40%Bi-Sb-Se-Te 400℃ isoplethal section, the(Bi2)m(Bi2(Se,Te)3)n single phase region and (Bi2)m(Bi2(Se,Te)3)n+Bi2(Se,Te)3 have been determined.