| Summary: | 碩士 === 國立中興大學 === 材料科學與工程學系所 === 102 === In this study, the type Ⅷ Ba8Ga16Sn30 clathrates were synthesized by means of the vertical Bridgman method from Sn flux, with staring ompostions Ba : Ga : Sn = 8 : 16 : 50. The effects of pulling rate on the rains size of Ba8Ga16Sn30 were investigated. The crystallinity and mposition 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. When we control the nucleation stage with slower pulling rate, the greater grain size we get. And the compound has the maximum grain sizes of 6 mm.
And then the P-type type- Ⅷ Ba8Ga16-ySn30-x+yAlx clathrates were synthesized by means of the vertical Bridgman method from Sn flux. We observed that adding Al makes grain size become smaller by metallography analysis. For Ba8Ga16-ySn30-x+yAlx, the temperature dependence of thermoelectric properties including the electrical conductivity, Seebeck coefficient and thermal conductivity were measured and discussed in this study. At 160℃ the Ba8.1Ga14.0Sn30.4Al1.6 sample has the optimal Seebeck coeifficient of 126 μV/K, while the electrical conductivity is 758 S/cm and the thermal conductivity is 1.73 W/mK. The figure of merit ZT reached the maximum value of 0.3 . Thermoelectric performance was expected because of wetting phase, but this study had confirmed that Al can dissolve in the clathrates, and P-type type Ⅷ Ba8Ga16-ySn30-x+yAlx compounds by Sn flux were successfully prepared.
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