The preparation and thermoelectric properties of the n-type BaGaSn clathrates prepared by vertical Bridgeman method.

• Main Authors: Qin-gang Hong, 洪欽港
• Other Authors: 張立信
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/96x9gy

碩士 === 國立中興大學 === 材料科學與工程學系所 === 101 === In this study, the N-type type-Ⅷ Ba8Ga16Sn30 compounds were synthesized by means of the vertical Bridgman method from Sn flux. The effects of starting composition and furnace temperature on the grains size of Ba8Ga16Sn30 were investigated. The crystallinity and composition of samples were respectively examined by X-ray and EDS. The results shows that the compound of samples formed is the type-Ⅷ clathrate Ba8Ga16Sn30. The furnace temperature was set at several temperatures in the range of 500 to 800℃ in the vertical Bridgman method. When the furnace temperature is 650℃, the compound has the maximum grain sizes of 4.5 mm and the average grain size of 2.4 mm at the atomic ratio of Ba : Ga : Sn = 8 : 16 : 50. When the temperature differs from 650℃, the grain size becomes smaller. With the increase of the initial flux amount at the atomic ratio of Ba : Ga : Sn = 8 : 16 : 60, the compound has the maximum grain sizes of 4.3 mm and average grain size of 2.0 mm when the furnace temperature is 600℃. The shape and diameter of the quartz tube were also changed in this study in order to increase the grain size. However the grain size was not increased. The temperature dependence of thermoelectric properties including the Seebeck coefficient, electrical conductivity and thermal conductivity were measured and discussed in this study. At 200℃ the Ba8Ga16Sn30 sample possesses the optimal Seebeck coeifficient of 260 μV/K, while the electrical conductivity is 167 S/cm and the thermal conductivity is 0.66 W/mK. The figure of merit ZT reached the maximum value of 0.81 at 200℃.