| Summary: | 碩士 === 國立中興大學 === 材料科學與工程學系所 === 107 === In the study, the N type Ba8Ga16Sn30 type-VIII clathrate was synthesized by the vertical solution Bridgeman method, and sliver was doped to Ba8Ga16Sn30. The effects of adding sliver on the crystal process and thermoelectric properties were investigated. Adding sliver to the raw solution reduces the grain size of Ba8Ga16Sn30 grown by the vertical solution Bridgeman method. When silver is doped into the Ba8Ga16Sn30 by thermal diffusion from surface layer coated by thermal evaporation ,the grain size of the Ba8Ga16Sn30 is not affected. The composition and crystallinity of samples were examined by energy-dispersive X-ray spectrometer, inductively coupled plasma mass-spectrometer and X ray-diffraction. The results shows that the compound formed is the type VIII clathrate.
The temperature dependence of thermoelectric properties including the Seebeck coefficient and electric conductivity of the samples were respectively measured. The thermal conductivity, power factor and thermoelectric figure of merit zT were calculated. At room temperature
the carrier concentration increases and the carrier mobility increases first and then decreases with the increase of silver content. The electrical conductivity increases first and then decreases with the increase of silver content. The Seebeck coefficient decreases with the increase of silver content. At 225 ℃, the sample with the sliver concentration of 380 ppm possessed the Seebeck coefficient of -169 μV/K, while its electrical conductivity is 240 S/cm and its thermal conductivity 0.79 W/m·K. The figure of merit zT is 0.43.
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