探討元素摻雜與 急冷懸鑄法對高錳矽化物之熱電性質影響;Explore the Effects of Element Doping and Melt-Spinning on Thermoelectric Properties of Higher Manganese Silicide

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Title:	探討元素摻雜與急冷懸鑄法對高錳矽化物之熱電性質影響;Explore the Effects of Element Doping and Melt-Spinning on Thermoelectric Properties of Higher Manganese Silicide
Authors:	蔣明勳;Jiang, Ming-Xun
Contributors:	材料科學與工程研究所
Keywords:	高錳矽化合物;熱電性質;元素摻雜;急冷旋鑄法;Higher Manganese Silicide;Thermoelectric Properties;Element Doping;Melt-Spinning
Date:	2024-08-20
Issue Date:	2024-10-09 15:44:25 (UTC+8)
Publisher:	國立中央大學
Abstract:	熱電材料能夠直接轉換熱能及電能，適合廢熱回收及無震動冷卻方面的應用。其中高錳矽化物(HMS)被視作在中高溫環境中一有潛力的P型熱電材料，其具有許多優點:元素含量充足、熱穩定性佳、對環境無害……等等，其應用性往往受限於其熱電轉換效率不佳及製造成本過高，始終無法被廣泛應用。本研究透過兩種策略來提高了HMS的熱電性能。第一個研究探討錫摻雜(Mn(Si1-xSnx)1.75, x = 0, 0.001, 0.005, 0.01, 0.015)對HMS系統的影響，此研究試樣是透過電弧熔煉和火花電漿燒結(SPS)等製程來製備。透過分析可觀察到錫在 x ≥ 0.005 時於基材中析出，可推論其溶解極限約為 x = 0.001。而以錫取代矽的方式會引入點缺陷，其造成的散射顯著降低了HMS的晶格熱導率。x = 0.001樣品的晶格熱導率值在750 K時降至此材料系統的最小值 2.0 W/mK，與未摻雜的 HMS 之值相比大幅降低了 47.4%。並在750 K時測得的熱電優值(ZT)約為0.31。接續第一個研究的成果，第二個研究利用急冷旋鑄的方式來製備薄帶狀的高錳矽化物，隨後以火花電將燒結的方式製備一奈米化塊材。此材料系統會引入奈米晶界，會增加低/中波長的聲子散射。此材料系統的錫的溶解度大約落在x=0.0025左右。結合上述兩種引入缺陷造成聲子散射的方式，會造成此材料系統的熱導率於750℃大幅下降至1.30 W/mK，其ZT值有效提升至0.482，與純相相比約有60%的提升。 ;Higher manganese silicides (HMS) are regarded as promising p-type thermoelectric materials in the mid-temperature range, owing to their earth-abundance and thermal stability. The limited thermoelectric performance of HMS in terms of their low figure-of-merit (ZT), is the main bottleneck for realizing an efficient HMS-based thermoelectric generator. We report significant enhancement in the thermoelectric performance of HMS with two strategies. The first one explores the impact of tin doping on the HMS system, which was synthesized via an arc-melting process and spark plasma sintering (SPS). Our findings reveal that metallic Sn precipitates within the Mn(Si1-xSnx)1.75 matrix at x ≥ 0.005, with a determined solubility limit of approximately x = 0.001. In addition, substituting Si with Sn effectively reduces the lattice thermal conductivity (kL) of HMS by introducing point defect scattering. In contrast to the undoped HMS, kL decreases to a minimum value of 2.0 W/mK at 750 K for the Mn(Si0.999Sn0.001)1.75 sample, marking a substantial 47.4% reduction. Consequently, a figure of merit (ZT) value of ~ 0.31 is attained at 750 K. Following the results of the first study, the second one used melt-spinning to prepare ribbons of HMS and then used SPS to prepare a nanobulk. This material system will introduce nanograin boundaries, which will increase the scattering of low/medium wavelength phonons. The solubility of tin in this system is around x = 0.025. Combining the above two methods, the kL of this material system drops significantly to 1.30 W/mK at 750°C, and its ZT is effectively increased to 0.482.
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