Effect of powder size and sintering temperature thermoelectric properties of sintered Bi0.5Sb1.5Te3 compounds

• Main Authors: Po-Chih Chen, 陳柏志
• Other Authors: Chien-Neng Liao
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/27218796880823865877

碩士 === 國立清華大學 === 材料科學工程學系 === 96 === 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.