The properties and microstructure of GeTe based thermoelectric materials

• Main Authors: Wang, Hong-Bin, 王鴻彬
• Other Authors: Tsau, Chun-Huei
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/32020195866658422083

碩士 === 中國文化大學 === 材料科學與奈米科技研究所 === 99 === Thermoelectric material is a material which can transform heat to electric or transform electric to heat. It can be a thermo cooler or thermo generator. The related compounds (AgSbTe2)1-x(GeTe)x (known collec- tively by the acronym of their constituent elements as TAGS-X, where x designates the mole fraction of GeTe) were first reported in the1960s and have since been successfully deployed in radioisotope thermoelectric generators for deep space and remote applications. The composition (AgSbTe2)0.15(GeTe)0.85 (TAGS-85) was found to have the best combination of thermal and electrical transport properties and mechanical stability. The key feature of TAGS-x for thermoelectric applications is the very low thermal conductivity for the compositions TAGS-80 and TAGS-85. The performance of materials for either of the above mentioned applications is governed by the thermoelectric figure of merit Z=S2/ρκ where S is the Seebeck coefficient, ρ is the electrical resistivity, and κ is the thermal conductivity. The dimension less figure of merit, ZT, can be obtained by multiplying Z by the absolute temperature (T). Higher Z values lead to more efficient materials and ultimately to more highly efficient devices. The thermal conductivity is too hard to get, so the Power factor = S2/ρ, also can be the thermoelectric figure of merit. In my study I select TAGS-85 to be my research material, as the composition is varied from AgSbTe2 to GeTe, the transport properties vary smoothly, except for an anomalous double minimum in thermal conductivity at 80 and 85% GeTe. Other researchers have reported ZT values as high as 1.7 in the TAGS-80 composition, however, its inferior mechanical strength led to more widespread use of TAGS-85, (AgSbTe2)0.15(GeTe)0.85, as the preferred composition. In many studies, they have different method to product the samples, such as different pressure, ingot cool down rates, different hot-press temperatures, hot-press time, particle size. So I use 200μm particle size, hot-press to product samples, the sample size is 8mm×8mm×15mm, the pressure is 38Mpa, I change hot-press temperature 350℃, 400℃, 450℃ 500℃, and hot-press time is 10min, 20min, 30min, and the ingot cool down rate have three rates, water quenching, air quenching, furnace quenching. The Seebeck coefficients is relationship with hot-press time 10min>20min>30min, the Seebeck coefficients at hot-press temperature 450℃ have the highest value, the electrical resistivity with water quenching > air quenching > furnace quenching. Why the Seebeck coefficients relationship with hot-press time? I think because of the grain boundary, the energy gap relationship with Seebeck coefficients, the electric need more energy to through the gap so the Seebeck coefficients have high value.