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二元单晶稀土六硼化物(REB6)具有丰富的物理性质, 其中单晶LaB6具有优异的电子发射特性, 影响二元REB6发射性能的物理机理及其他二元REB6是否具有良好的发射特性, 需要进一步研究. 本文采用基于密度泛函理论的第一性原理计算对典型二元单晶REB6 (RE = La, Ce, Pr, Nd, Sm, Gd)的电子结构、功函数进行了理论分析, 并对区熔法制备的高质量单晶REB6的热发射性能进行了测试. 电子结构计算结果表明, 二元REB6费米能级附近具有很高的态密度, 宽域分布的稀土元素的d电子决定了REB6优异发射性能的电子态, 局域分布的f轨道对发射性能不利. 功函数理论计算表明具有d态价电子的二元REB6 (RE = La, Ce, Gd)具有较低功函数. 热发射测试结果表明, 以上单晶REB6 (100)晶面功函数热发射测试值与理论计算值基本相符. 最终理论计算结合实验结果表明, LaB6和CeB6具有良好的热发射和场发射性能, GdB6具有良好的场发射性能.Binary rare earth hexaborides (REB6) have different rare earth elements with different valence electron distributions, which lead to different strange physical properties and different emission properties. However, in the electron emission properties, whether PrB6, NdB6, SmB6 and GdB6 all have excellent emission properties remains to be further studied, and the physical mechanism affecting their emission properties needs investigating. In this paper, the electronic structures, work functions of typical binary single crystal REB6 (LaB6, CeB6, PrB6, NdB6, SmB6, GdB6) are studied by first principles calculations. The single crystal REB6 are prepared by optical zone melting method, and their thermionic electron emission properties are tested experimentally. The theoretical calculation results show that the typical binary REB6 have large densities of states near the Fermi level. The d-orbitals with broad distributions in conduction bands are beneficial to electron emission. The localized f-orbital electrons in valence bands are not conducive to their electron emission. The theoretical calculations of work functions of typical binary single crystal REB6 (100) surface are consistent with the analyses of their electronic structures. The theoretical calculation values of work functions are ordered as GdB6 (2.27 eV) < CeB6 (2.36 eV) < LaB6 (2.40 eV) < PrB6 (2.58 eV) < SmB6 (2.63 eV) < NdB6 (2.91 eV). The experimental test results of thermionic electron emission of single crystal show that the experimental thermionic electron properties are consistent with the theoretical ones. The LaB6 and CeB6 both have good thermionic and field emission properties, and the GdB6 has excellent field emission properties.
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Keywords:
- single crystal REB6 /
- first principles /
- work function /
- thermionic emission
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图 3 典型二元REB6的总态密度
Fig. 3. Calculated electronic total density of states (DOS) of binary REB6.
图 4 典型二元REB6的RE元素的分态密度
Fig. 4. Calculated electronic partial density of states (PDOS) of binary REB6.
图 5 (a) REB6 (100)晶面的Slab模型; (b)计算获得的典型二元REB6 (100)晶面的费米能级和真空能级
Fig. 5. (a) Slab model of REB6 (100) surface; (b) the calculated Fermi energy and vacuum energy of binary REB6 (100) surface.
图 6 光学区熔制备的典型二元单晶REB6 (a)实物照片; (b)摇摆曲线
Fig. 6. Single crystal REB6 prepared by optical zone melting: (a) Photos; (b) rocking curves.
图 7 单晶REB6 (100)晶面的热发射电流密度
Fig. 7. Thermionic emission current density of single crystal REB6 (100) surfaces.
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[1] Duan J, Zhou T, Zhang L, Du J G, Jiang G, Wang H B 2015 Chin. Phys. B 24 096201
Google Scholar
[2] Zhang H, Tang J, Yuan J, Yamauchi Y, Suzuki T T, Shinya N, Nakajima K, Qin L C 2016 Nat. Nanotechnol. 11 273
Google Scholar
[3] 包黎红, 张久兴, 周身林, 张宁 2011 60 106501
Google Scholar
Bao L H, Zhang J X, Zhou S L, Zhang N 2011 Acta Phys. Sin. 60 106501
Google Scholar
[4] Zhou N, Zhang W, Zhang X, Liu H, Lu Q, Xiao Y, Liu Y, Jin S, Liao N 2021 Vacuum 184 109929
Google Scholar
[5] Hoyoung J, Friemel G, Ollivier J, Dukhnenko A V, N Yu S, Filipov V B, Keimer B, Inosov D S 2014 Nat. Mater. 13 682
Google Scholar
[6] Wang Y, Zhao J, Yang X, Cheng H, Xu B, Ning S, Zhang J 2019 Cryst. Res. Technol. 54 1800276
Google Scholar
[7] Stankiewicz J, Evangelisti M, Fisk Z 2011 Phys. Rev. B 83 113108
Google Scholar
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Google Scholar
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Google Scholar
[10] Paul S, Dohun K, Michael S F, Johnpierre P 2015 Phys. Rev. Lett. 114 096601
Google Scholar
[11] Sundermann M, Yavaş H, Chen K, Kim D J, Fisk Z, Kasinathan D, Haverkort M W, Thalmeier P, Severing A, Tjeng L H 2018 Phys. Rev. Lett. 120 016402
Google Scholar
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Google Scholar
[13] Mackenzie A P, Hicks C W 2017 Nat. Mater. 16 702
Google Scholar
[14] Swanson L W, Mcneely D R 1979 Surf. Sci. 83 11
Google Scholar
[15] Bao L H, Zhang J X, Zhou S L, Zhang N, Xu H 2011 Chin. Phys. Lett. 28 088101
Google Scholar
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Google Scholar
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Google Scholar
[18] Weng H M, Zhao J Z, Wang Z J, Fang Z, Dai X 2014 Phys. Rev. Lett. 112 016403
Google Scholar
[19] Lu F, Zhao J Z, Weng H M, Fang Z, Dai X 2013 Phys. Rev. Lett. 110 096401
Google Scholar
[20] Qin X, Liu X, Huang W, Bettinelli M, Liu X 2017 Chem. Rev. 117 4488
Google Scholar
[21] Elkelany K E, Ravoux C, Desmarais J K, Cortona P, Pan Y, Tse J S, Erba A 2018 Phys. Rev. B 97 245118
Google Scholar
[22] 包黎红, 那仁格日乐, 特古斯, 张忻, 张久兴 2013 62 196105
Google Scholar
Bao L H, Narengerile, Tegus O, Zhang X, Zhang J X 2013 Acta Phys. Sin. 62 196105
Google Scholar
[23] Liu H, Zhang X, Ning S, Xiao Y, Zhang J 2017 Vacuum 143 245
Google Scholar
[24] 刘洪亮, 张忻, 王杨, 肖怡新, 张久兴 2018 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
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