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[Ca24Al28O64]4+(4e–)电子化合物是一种具有高载流子密度、低逸出功的透明导电氧化物, 但是繁琐的制备步骤、苛刻的工艺条件极大地限制了其实际应用. 本文以特定化学计量比的Ca12Al14O33+CaAl2O4两相为前驱体, 在放电等离子烧结系统里通过原位钙热反应成功制备了多晶C12A7:e–. 在烧结温度为1100 ℃, 保温时间为10 min的条件下, 其电子浓度基本达到理论最大值~2.3×1021 cm–3, 在2.5 eV处出现明显的紫外吸收峰, 致密度可达99%以上. 同时用顺磁共振谱仪分析了其电子结构, 结果呈Dyson特性, 这些结果充分证明了电子有效地注入到笼腔结构中. 热电子发射测试结果显示: 在阴极温度为1373 K, 外加电场为35000 V/cm的条件下, C12A7:e–的热发射电流密度为1.75 A/cm2, 有效逸出功为2.07 eV. 该工艺提供了一种新型的电子注入方法, 大幅度缩短了制备周期使大规模生产成为可能.[Ca24Al28O64]4+(4e–) eletride, as the first room-temperature stable inorganic electride, has attracted intensive attention because of its fascinating chemical, electrical, optical, and magnetic properties. However, it usually needs synthesizing through a complicated multistep process involving high temperature (e.g., 1350 °C), severe reduction (e.g., 700–1300 ℃ for up to 240 h in Ca or Ti metal vapor atmosphere) and post-purification. Owing to the H2O sensitivity of mayenite, the post-purification is quite troublesome once impurities are introduced. High-density, loosely bound encaged electrons with a low work function make it promise to possess practical applications. Therefore the facile method of massively producing the high-quality C12A7:e– with high Ne is extremely desired. In this work, C12A7:e– bulks are for the first time synthesized by simple spark plasma sintering process directly from a mixture of C12A7, CA and Ca powders under milder conditions (e.g., sintered at 1070 ℃ for 10 min in a vacuum). The obtained electride, which exhibits a relative density of 99%, an electron concentration of ~2.3×1021 cm–3 and an obvious absorption peak at 2.5 eV, is obtained via SPS process at 1100 ℃ for 10 min. Electronic structure is also investigated by electron paramagnetic resonance. The occurrence of Dysonian characteristic, a typical feature of good electronic conductors, strongly suggests that the electrons are trapped in mayenite cavities. Furthermore, the obtained C12A7:e– exhibits good sinterabilty on a crystal scale of 5–40 μm. Thermionic emission test results show that the thermionic emission begins to occur at 700 K and a large current density of 1.75 A/cm2 is obtained in the electron thermal emission from a flat surface of the polycrystalline C12A7:e– with an effective work function of 2.09 eV for a temperature of 1373 K with an applied electric field of ~35000 V/cm in a vacuum. Owing to no external reductant is needed, this developed route exhibits notable superiority over the conventional reduction method for phase-pure C12A7:e–. Therefore, these results not only suggest a novel precursor for fabricating mayenite electride but also make it possible to produce efficiently the electride in large volume.
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Keywords:
- C12A7:e– /
- calciothermic reaction /
- thermionic emission
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图 1 C12A7+CA混合前驱体烧结前后XRD与实物照片
Fig. 1. Powder X-ray diffraction patterns of precursor before and after SPS process, insets are digital pictures of the precursor and the obtained electride.
图 3 (a) 样品的顺磁共振图谱; (b) 样品的紫外吸收光谱
Fig. 3. (a) EPR spectra of the sintered C12A7 bulk; (b) optical absorption spectra of the sintered C12A7:e– powders.
图 4 (a) 不同温度下发射电流密度随电场强度的变化; (b) 零场电流密度的拟合直线; (c) Richardson直线; (d) 发射稳定性曲线
Fig. 4. (a) Emission current density as a function of electric field at various in the range of 973 to 1373 K; (b) Schottky plots at various temperatures, fitting of the curves result in zero field emission current density at each temperature; (c) Richardson plot of the sample; (d) scatter plot of the emission current density versus time.
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[1] Dye J L 2009 Acc. Chem. Res. 42 1564
Google Scholar
[2] Kim S W, Hosono H 2012 Philos. Mag. 92 2596
Google Scholar
[3] Jiang D, Zhao Z Y, Mu S L, Qian H J, Tong J H 2018 Inorg. Chem. 58 960
[4] Khan K, Tareen A K, Elshahat S, Yadav A, Khan U 2018 Dalton Trans. 47 3819
Google Scholar
[5] Matsuishi S, Toda Y, Miyakawa M 2003 Science 301 626
Google Scholar
[6] 刘洪亮, 张忻, 王杨, 肖怡新, 张久兴 2018 物理学报 67 048101
Google Scholar
Liu H L, Zhang X, Wang Y, Xiao Y X, Zhang J X 2018 Acta Phys. Sin. 67 048101
Google Scholar
[7] Kitano M, Inoue Y, Yamazaki Y, Fumitaka H, Shinji K, Satoru M, Toshiharu Y, Sung W K, Michikazu H, Hideo H 2012 Nat. Chem. 4 934
Google Scholar
[8] Kim S W, Hayashi K, Hirano M, Hosono H, Tanaka I 2006 J. Am. Ceram. Soc. 89 3294
Google Scholar
[9] Kitano M, Kanbara S, Inoue Y, Kuganathan N, Sushko P V, Yokoyama T, Hara M, Hosono H 2015 Nat. Commun. 6 6731
Google Scholar
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Google Scholar
[11] Ding Y F, Zhao Q Q, Yu Z L, Zhao Y Q, Liu B, He P B, Zhou H, Li K L, Yin S F, Cai M Q 2019 J. Mater. Chem. C 7 7433
Google Scholar
[12] Zhao Y Q, Wang X, Liu B, Yu Z L, He P B, Wan Q, Cai M Q, Yu H L 2018 Org. Electron. 53 50
Google Scholar
[13] Dye J L 2003 Science 301 607
Google Scholar
[14] Toda Y, Kim S W, Hayashi K, Hirano M, Kamiya T, Hosono H, Yasuda H 2005 Appl. Phys. Lett. 87 254103
Google Scholar
[15] Yu Z L, Ma Q R, Liu B, Zhao Y Q, Wang L Z, Zhou H, Cai M Q 2017 J. Phys. D: Appl. Phys. 50 465101
Google Scholar
[16] Zhao Y Q, Ma Q R, Liu B, Yu Z L, Yang J L, Cai M Q 2018 Nanoscale 10 8677
Google Scholar
[17] Deng X Z, Zhao Q Q, Zhao Y Q, Cai M Q 2019 Current Appl. Phys. 19 279
Google Scholar
[18] Kim K B, Kikuchi M, Miyakawa M, Yanagi H, Kamiya T, Hirano M, Hosono H 2007 J. Phys. Chem. C 111 8403
Google Scholar
[19] Kou X C, Kronmüller H, Givord D, Rossignol M F 1994 Phys. Rev. B 50 3849
Google Scholar
[20] Matsuishi S, Nomura T, Hirano M, Kodama K, Shamoto S I, Hosono H 2009 Chem. Mater. 21 2589
Google Scholar
[21] Kim S W, Matsuishi S, Nomura T, Kubota Y, Takata M, Hayashi K, Hosono H 2007 Nano Lett. 7 1138
Google Scholar
[22] Hosono H, Hayashi K, Hirano M 2007 J. Mater. Sci. 42 1872
Google Scholar
[23] Sushko P V, Shluger A, Hayashi K, Hirano M, Hosono H 2003 Phys. Rev. Lett. 9 126401
[24] Miyakawa M, Toda Y, Hayashi K, Hirano M, Kamiya T, Matsunami N, Hosono H 2005 J. Appl. Phys. 97 023510
Google Scholar
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[26] 冯琦, 张忻, 刘洪亮, 赵吉平, 李凡, 张久兴 2018 物理学报 67 047102
Google Scholar
Feng Q, Zhang X, Liu H L, Zhao J P, Xiao Y X, Li F, Zhang J X 2018 Acta Phys. Sin. 67 047102
Google Scholar
[27] Duan J, Zhou T, Zhang L, Du J G, Jiang G, Wang H B 2015 Chin. Phys. B 24 096201
Google Scholar
[28] Yu Z, Okoronkwo M U, Sant G N, Misture S T, Wang B 2019 J. Phys. Chem. C 123 11982
Google Scholar
[29] Matsuishi S, Kim S W, Kamiya T, Hirano M, Hosono H 2008 J. Phys. Chem. C 112 4753
Google Scholar
[30] Li F, Zhang X, Liu H L, Zhao J P, Xiao Y X, Zhang J X 2019 J. Am. Ceram. Soc. 102 884
[31] Li F, Zhang X, Liu H L, Zhao J P, Xiao Y X, Zhang J X 2018 Vacuum 158 152
Google Scholar
[32] 包黎红, 那仁格日乐, 特古斯, 张忻, 张久兴 2013 物理学报 62 196105
Google Scholar
Bao L H, Narengerile, Tegus O, Zhang X, Zhang J X 2013 Acta Phys. Sin. 62 196105
Google Scholar
[33] Konovalov S, Zagulyaev D, Chen X Z, Gromov V, Ivanov Y 2017 Chin. Phys. B 26 126203
Google Scholar
[34] Xue J J, Cai Q, Zhang B H, Gei M, Chen D J, Zhi T, Chen J W, Wang L H, Zhang R, Zhen Y D 2017 Chin. Phys. B 26 116801
Google Scholar
[35] Zhou S, Zhang J, Liu D, Lin Z, Huang Q, Bao L, Ma R, Wei Y 2010 Acta Mater. 58 4978
Google Scholar
[36] Zhao G P, Zhao M G, Lim H S, Feng Y P, Ong C K 2005 Appl. Phys. Lett. 87 162513
Google Scholar
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