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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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[1] Duan J, Zhou T, Zhang L, Du J G, Jiang G, Wang H B 2015 Chin. Phys. B 24 096201Google Scholar
[2] Zhang H, Tang J, Yuan J, Yamauchi Y, Suzuki T T, Shinya N, Nakajima K, Qin L C 2016 Nat. Nanotechnol. 11 273Google Scholar
[3] 包黎红, 张久兴, 周身林, 张宁 2011 物理学报 60 106501Google Scholar
Bao L H, Zhang J X, Zhou S L, Zhang N 2011 Acta Phys. Sin. 60 106501Google Scholar
[4] Zhou N, Zhang W, Zhang X, Liu H, Lu Q, Xiao Y, Liu Y, Jin S, Liao N 2021 Vacuum 184 109929Google 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 682Google Scholar
[6] Wang Y, Zhao J, Yang X, Cheng H, Xu B, Ning S, Zhang J 2019 Cryst. Res. Technol. 54 1800276Google Scholar
[7] Stankiewicz J, Evangelisti M, Fisk Z 2011 Phys. Rev. B 83 113108Google Scholar
[8] Nikitin S E, Portnichenko P Y, Dukhnenko A V, Shitsevalova N Y, Filipov V B, Qiu Y, Rodriguezrivera J A, Ollivier J, Inosov D S 2018 Phys. Rev. B 97 075116Google Scholar
[9] Zhang H, Zhang Q, Zhao G P, Tang J, Zhou O, Qin L C 2005 J. Am. Chem. Soc. 127 13120Google Scholar
[10] Paul S, Dohun K, Michael S F, Johnpierre P 2015 Phys. Rev. Lett. 114 096601Google 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 016402Google Scholar
[12] Liu T, Li Y, Gu L, Ding J, Chang H, Janantha P, Kalinikos B, Novosad V, Hoffmann A, Wu R 2018 Phys. Rev. Lett. 120 207206Google Scholar
[13] Mackenzie A P, Hicks C W 2017 Nat. Mater. 16 702Google Scholar
[14] Swanson L W, Mcneely D R 1979 Surf. Sci. 83 11Google Scholar
[15] Bao L H, Zhang J X, Zhou S L, Zhang N, Xu H 2011 Chin. Phys. Lett. 28 088101Google Scholar
[16] Futamoto M, Nakazawa M, Kawabe U 1980 Surf. Sci. 100 470Google Scholar
[17] Olsen G H, Cafiero A V 1978 J. Cryst. Growth. 44 287Google Scholar
[18] Weng H M, Zhao J Z, Wang Z J, Fang Z, Dai X 2014 Phys. Rev. Lett. 112 016403Google Scholar
[19] Lu F, Zhao J Z, Weng H M, Fang Z, Dai X 2013 Phys. Rev. Lett. 110 096401Google Scholar
[20] Qin X, Liu X, Huang W, Bettinelli M, Liu X 2017 Chem. Rev. 117 4488Google Scholar
[21] Elkelany K E, Ravoux C, Desmarais J K, Cortona P, Pan Y, Tse J S, Erba A 2018 Phys. Rev. B 97 245118Google Scholar
[22] 包黎红, 那仁格日乐, 特古斯, 张忻, 张久兴 2013 物理学报 62 196105Google Scholar
Bao L H, Narengerile, Tegus O, Zhang X, Zhang J X 2013 Acta Phys. Sin. 62 196105Google Scholar
[23] Liu H, Zhang X, Ning S, Xiao Y, Zhang J 2017 Vacuum 143 245Google Scholar
[24] 刘洪亮, 张忻, 王杨, 肖怡新, 张久兴 2018 物理学报 67 048101Google Scholar
Liu H L, Zhang X, Wang Y, Xiao Y X, Zhang J X 2018 Acta Phys. Sin. 67 048101Google Scholar
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