Preparation of Bi2Te3-based thermoelectric nanocomposites by powder metallurgy method

• Main Authors: Tz-Yuan Chao, 趙子元
• Other Authors: Pee-Yew Lee
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/41148436516794176494

碩士 === 國立臺灣海洋大學 === 材料工程研究所 === 100 === Abstract During mechanical alloying of Bi and Te elemental powder mixture, it is found the Bi2Te3 compound phase can be formed in a very short time of 60 seconds, the mechanically alloyed powders was completely transformed into Bi2Te3 phase with further milling to 15mins. The Bi0.4Sb1.6Te3 and Bi2Te2.4Se0.6 compound phase with 20 nm grain size can be obtained using the same method with stoichiometric composition after 2 hours of mechanical alloying treatment. A Ti50Cu28Ni15Sn7 amorphous powder was formed by 8 hours mechanical alloying of corresponding elemental mixtures. These amorphous powders were further milling with Bi and Te elemental powders and the Ti50Cu28Ni15Sn7 / Bi2Te3 composite powders with Ti50Cu28Ni15Sn7 amorphous particles inside nanostructured Bi2Te3 matrix were successfully prepared after 2 hours ball milling. The Ti50Cu28Ni15Sn7 / Bi2Te3 composite powders can be consolidated into bulk samples with a diameter of 20 mm and thickness of 8mm using by vacuum hot pressing. The microstructure of Ti50Cu28Ni15Sn7 / Bi2Te3 bulk samples shows that micro-scale Ti50Cu28Ni15Sn7 amorphous particles were homogeneously distributed inside nanostructured Bi2Te3 matrix. In addition, the Te precipitates were observed for the bulk samples consist of low purity Te. An unknown phase around amorphous particles was also found and it is suggested that the reaction between Te precipitates and amorphous phase was responsible. The thermoelectric properties of Ti50Cu28Ni15Sn7 / Bi2Te3-based samples were measured. The results indicated a very low ZT values were detected for the Ti50Cu28Ni15Sn7 / Bi2Te3 samples due to impurity effect. However, for bulk 0.75 wt. % Ti50Cu28Ni15Sn7/ Bi0.4Sb1.6Te3 thermoelectric composite, a ZT value of 1.08 at 306℃ was obtained. This is the highest ZT values among the exists thermoelectric materials at 300℃. Keywords:,mechanical alloying, Bi2Te3, Ti50Cu28Ni15Sn7, vacuum hot pressing, thermoelectric nanocomposites, amorphous, Seebeck coefficient, ZT