以靜電紡絲技術製備一維鍺化鎂材料 之熱電性質研究

Study on Thermoelectric Properties in One-dimensional Mg Germanide Materials Fabricated Using Electrospinning Method

林協昌(Hsieh-Chang Lin)

指導教授 ： 李勝偉

國立中央大學/工學院/材料科學與工程研究所/碩士(2015年)

摘要

鍺化鎂 (Mg germanide) 是應用在中溫區間的熱電材料，由於具有窄能隙特徵、高成本效益、對環境較無害、組成元素蘊藏量豐富，被認為是具有潛力的熱電材料。本實驗利用靜電紡絲法 (Electrospinning method) 搭配高真空熱阻式蒸鍍系統 (Thermal Coater System) 分別鍍上鎂、鍺薄膜，藉由調變鎂和鍺沉積的薄膜比例，製備出鍺化鎂的一維奈米結構，並探討不同比例在300～600 K區間的熱電性質 (Thermoelectric properties)。
由靜電紡絲法製備的PVP奈米纖維在熱蒸鍍過程作用為模板，可經過熱退火移除並留下溝渠形貌的鍺化鎂薄膜。當材料電導率上升，熱導率也會上升，因此無法藉由單純的提升電導率來增加ZT值，製備成一維的奈米結構後，利用材料的表面散射 (surface boundary scattering) 和晶界散射 (grain boundary scattering) 的機制已經是一個有效降低熱導率的方法，由不同元素組成的鎂鍺化合物，合金散射 (alloy scattering) 對於阻礙高頻聲子更扮演了重要的角色，控制厚度比例製備出三種不同的奈米溝渠分別是鍺化鎂 (Mg2Ge)、鍺化鎂+鍺複合相 (Mg2Ge+Ge) 以及鍺化鎂+鎂複合相 (Mg2Ge +Mg)，而鍺化鎂+鍺複合相 (Mg2Ge+Ge) 奈米溝渠其ZT值在600 K時達到0.45。

關鍵字

鍺化鎂 ； 一維奈米結構 ； 熱電效應

並列摘要

Thermoelectric (TE) material Mg germanide, which is applicable in mid-temperature and has the advantages of narrow bandgap, cost-efficiency, environment friendly properties and the abundant constituent element, is regarded as a potentially promising thermoelectric material. In this study, we utilized electrospinning method and thermal coater system to fabricated one-dimensional Mg germanide nanostructures of different deposition ratio of germanium and magnesium. Their thermoelectric of properties different deposition ratio have been investigated in the temperature range of 300～600 K.
PVP nanofibers are synthesized by electrospinning method and used as the template in evaporation process. After being annealed, PVP nanofibers would be removed and Mg germanide nanotroughs remain. It is difficult to increase the ZT value by enhancing the conductivity due to concurrently increased thermal conductivity. Therefore, we fabricate one-dimensional nanostructures to reduce their thermal conductivity by surface scattering and grain boundary scattering. For Mg germanides consisting of different elements, alloy scattering plays an important role to hinder high-frequency phonons, and thus enhance of the ZT value. Three kind of nanotroughs can be fabricated by controlling its thickness ratio. There are Mg2Ge, Mg2Ge+Ge, and Mg2Ge+Mg, respectively. The ZT value in Mg2Ge+Ge nanotrough reaches 0.45 at 600 K.

參考文獻

[32] R. Chen, "Nanowires for Thermal Energy Conversion and Management," ProQuest, (2008).

[1] R. Viennois, P. Jund, C. Colinet, and J.-C. Tédenac, "Defect and phase stability of solid solutions of Mg 2 X with an antifluorite structure: An ab initio study," Journal of Solid State Chemistry, 193, 133-136 (2012).

[2] D. M. Rowe, "Thermoelectrics Handbook: Macro to Nano," Taylor & Francis, (2005).

[3] P. Jund, R. Viennois, C. Colinet, G. Hug, M. Fèvre, and J.-C. Tédenac, "Lattice stability and formation energies of intrinsic defects in Mg2Si and Mg2Ge via first principles simulations," Journal of Physics: Condensed Matter, 25, 035403 (2013).

[4] L. E. Bell, "Cooling, heating, generating power, and recovering waste heat with thermoelectric systems," Science, 321, 1457-1461 (2008).