摻In合金化和熱鍛增強的中溫熱電材料n型碲化鉍基合金的研究

熱電(TE)材料能夠實現熱和電的直接相互轉換。

由於化石燃料的在過去二十年中日益增長的能源需求，現已經無法滿足日益增長的需要。熱電材料的開發和應用受到了廣泛的關注。 熱電裝置的轉換效率是直觀的表徵數據。其中Seebeck係數，電導率和熱導率(包括晶格貢獻和載流子貢獻)，以及工作溫度都是需要考量的重點。近年來，能帶工程和聲子工程分別用於優化電子和熱輸運性能，以最大限度地提高性能，包括能帶收斂、聲子散射、納米結構和引入點缺陷等都是改良性能的好方法。在發電方面，一些良好的TE材料在700K以上的工作溫度下表現優異，如PbTe、半Heusler合金等。然而，在400-700K的溫度範圍內，鮮有報到。但是對於餘熱收集的TE材料，開發並應用於400-700K溫度內，高效的TE材料在實踐中具非常重要的應用前景。

浙江大學朱鐵軍教授、趙新兵教授課題組，通過合金化和熱變形增強等方法提升了中溫熱電材料n型碲化鉍基合金的熱電性能，相關研究成果發表在Journal of Materiomics第4卷第3期，題目為Enhanced thermoelectric performance of n-type bismuth-telluride-based alloys via In alloying and hot deformation for mid-temperature power generation。您可以點擊文末「閱讀全文」免費下載！

Feng Li, Renshuang Zhai, Yehao Wu, Zhaojun Xu, Xinbing Zhao, Tiejun Zhu. Enhanced thermoelectric performance of n-type bismuth-telluride-based alloys via In alloying and hot deformation for mid-temperature power generation,Journal of Materiomics 2018; 4 (31): 208-214.

內容概述

碲化鉍基合金是用於室溫製冷的最廣泛商用熱電材料。通過合金化摻銦和熱變形等工藝的，成功地將n型鉍-碲化鉍基熱電材料用於中溫發電的應用中。採用SbI3摻雜調節載流子濃度並協同銦合來增加帶隙，抑制中溫範圍內的雙極傳導。由於熱變形引起的多尺度微結構的產生，使得熱導率顯著降低。通過實驗表明,熱變形後的Bi1.85In0.15Te2Se+0.25wt% SbI3合金在625K處達到∼1.1的zT峰值，顯示了該合金在中溫TE發電中的巨大應用前景。

Fig. 1. Previous study on band gap of Bi2Te3-xSex

Fig.1顯示了n型Bi2Te3-x性能帶隙隨成分的變化趨勢。與先前的結果達成一致，即Eg在x=1(Bi2Te2Se)處達到最大值，而它在x=3(Bi2Se3)處卻不一致。因此，我們在本工作中選擇Bi2Te2Se作為基體組成。

Fig. 2. XRD patterns of zone melted samples of Bi2-xInxTe2Se +0.25 wt% SbI3 (x = 0–0.20).

如Fig.2所示，ZM Bi2-xInxTe2Se-0.25wt% SbI3系列樣品中沒有觀察到二次相。在製備n型Bi2Te2Se熔化鋼錠過程中，Se和Te原子由於其較低的沸點而比B元素更易揮發，從而使得VTe..和VSe..陰離子空位。過量的Bi原子會佔據Te和Se空位，形成帶負電荷的反位缺陷，導致空穴濃度的增加。

Fig. 3. (a) Carrier concentration nH, and (b) Hall mobility, as a function of In content x in Bi2-xInxTe2Se + 0.25 wt% SbI3 (x = 0–0.2) samples before and after hot deformation.

Fig. 3(a)顯示了Bi2-xInxTe2Se中載流子濃度nH隨In含量的變化。隨著In含量的增加，載流子濃度先增大後減小。取代在Bi位點不產生更多的空穴或電子。因此，載流子濃度的變化應由本徵點缺陷引起。Fig. 3(b)顯示In含量x對室溫載流子遷移率μH的影響。所有樣品的μH隨著In含量的增加而減小，這主要是由於載流子的合金散射增強所致。

Fig. 4. (a) Electrical conductivity, and (b) Seebeck coefficient as a function of temperature for the Bi2-xInxTe2Se + 0.25 wt% SbI3 (x = 0–0.2) samples before and after hot deformation.

Fig. 4(a)顯示樣品電導率的溫度和含量相關性。σ的變化與載流子濃度的In含量依賴性很好地一致)。由於移動性μH的減少, HD樣本的σ值系統地低於ZM樣本。Fig. 4(b)給出了樣品α的溫度依賴性。ZM和HD樣品的Seebeck係數α首先下降，然後隨著含量x（0-0.20）的增加而上升，對應於圖中nH的變化。HD樣品α的降低主要歸因於載體濃度的增加。

Fig. 5. Band gap variation as a function of In content in the ZM Bi2-xInxTe2Se + 0.25 wt% SbI3 (x = 0–0.2) samples.

隨著合金化的增加，帶隙明顯增大，αmax溫度升高。由於合金化過程中Se損失的變化很小，Se缺乏對帶隙增加的影響可以忽略不計。因此，In合金化直接增加了帶隙。

Fig. 6. (a) Temperature dependence of total thermal conductivity κ and (b) room temperature lattice thermal conductivity (κ-κe) as a function of In content x of all Bi2-xInxTe2Se+0.25 wt%SbI3 (x = 0–0.20) ZM and HD samples.

合金化和熱變形對所有樣品熱導率的影響如上圖所示。對於簡併半導體，ZM和HD樣品的總導熱率κ首先略有上升，然後隨著In含量x的增加而下降，這是根據Wiedemann-Franz關係預估的。

Fig. 7. (a) Crystal unit cell; (b) Extended view; (c) Simulated HRTEM image [210]; (d) HRTEM image along [210] shows five-layer layered structure, matching with model, of HD Bi1.85In0.15Te2Se+0.25 wt%SbI3 sample.

Fig. 7顯示了HD Bi1.85In0.15Te2Se+0.25wt%SbI3樣品的層狀結構，與Bi2Te3基材料的晶體結構一致。

Fig. 8. (a) Low-magnification TEM image, contrast difference due to strain field; (b) Med-magnification TEM image, like platelet precipitate, the inset is enlarged view; (c) HRTEM image from (b); (d) HRTEM image showing strain-field domain; (e) and (f) IFFT images of region in (d) marked with blue box, (e) is obtained from one set of reflection spots marked with green circle, showing dislocations; (f) is obtained from one set of reflection spots marked purple circle, showing free of dislocation. (e) and (f) reflect the strain state is anisotropy of HD Bi1.85In0.15Te2Se+0.25 wt%SbI3 sample.

Fig. 9. (a) Temperature dependence of zT of all Bi2-xInxTe2Se + 0.25 wt% SbI3 (x = 0–0.20) ZM and HD samples, (b) Temperature dependent zT values for the n-type V-VI compounds in different temperature ranges.

亮點

• In alloying successfully broadens the band gap of Bi2Te2Se alloys, suppressing the bipolar effect at higher temperatures.
• The lattice thermal conductivity was greatly reduced by multiscale phonon scattering.
• Hot deformed n-type Bi1.85In0.15Te2Se+0.25 wt% SbI3 sample shows excellent TE performance in the range of 500–700K.

作者介紹

Feng Li is a Master student of School of Materials Science and Engineering, Zhejiang University. He has been working on bismuth-telluride-based thermoelectric compounds under the supervision of Prof. Tiejun Zhu. He was awarded Bachelor of Engineering Degree in Materials Science and Engineering from Zhejiang University, China, in 2016.

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