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系统研究了多功能多元稀土六硼化物La1–x Srx B6纳米粉末的光吸收及多晶块体的热电子发射性能. 纳米粉体光吸收结果表明, 多元稀土六硼化物La1–x SrxB6透射光波长从591 nm至658 nm连续可调. 多晶块体热电子发射结果表明, 外加电压2000 V, 阴极温度为1773 K时, 热电子发射电流密度从2.3 A/cm2线性增大至19.36 A/cm2, 表现出了热发射性能增强效果. 因此, 多元稀土六硼化物La1–x Srx B6为一种多功能材料, 在光吸收材料及热阴极材料领域具有潜在的应用前景. 此外, 为了揭示上述光吸收及热发射机理, 采用第一性原理系统计算体等离子共振频率能量和费米能级变化规律.The optical absorption property of the nanocrystalline La1–x Srx B6 powder and thermionic emission property of the La1–x Srx B6 polycrystalline bulk are investigated. As a result, the transmission wavelength of LaB6 is red-shifted from 591 nm to 658 nm with the increase of Sr doping content. The emission tests indicate that the thermionic emission current density of La1–x Srx B6 polycrystalline bulk increases from 2.3 A/cm2 to 19.36 A/cm2 with the increase of La doping content under an applied voltage of 2000 V. The first-principle calculation results reveal that Sr doping LaB6 leads plasma frequency energy and Fermi level to decrease, resulting in the tunable characteristics of transmission wavelength and enhancement of thermionic emission. Therefore, the Sr-doped LaB6 as a multifunctional ceramic has a potential application in the field of optical filter or becomes a promising cathode for microwave device.
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Keywords:
- LaB6 nanocrystalline /
- optical absorption /
- thermionic emission
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图 1 La0.825Sr0.125B6晶体结构示意图
Fig. 1. Schematic diagram of the La0.825Sr0.125B6 crystal structure.
图 2 (a)不同反应温度下制备的La0.4Sr0.6B6纳米颗粒的XRD谱图; (b) 1150 ℃下制备的La1–x Srx B6纳米颗粒的XRD谱图
Fig. 2. (a) XRD pattern of La0.4Sr0.6B6 nanoparticles prepared at different reaction temperatures; (b) XRD pattern of La1–x Srx B6 nanoparticles prepared at 1150 ℃.
图 3 不同反应温度下所制备的纳米La1–x Srx B6 (x = 0.2, 0.4, 0.6, 0.8)粉末SEM照片 (a)—(d)反应温度为1150 ℃; (e)—(h)反应温度为1200℃. 最底层为纳米La0.4Sr0.6B6粉末元素分布及EDS分析
Fig. 3. SEM image of La1–x Srx B6 (x = 0.2, 0.4, 0.6, 0.8) nanoparticles (a)−(d) prepared at 1150 ℃, (e)−(h) prepared at 1200 ℃. The lowest side shows the elements mapping and EDS analysis of La0.4Sr0.6B6 nanoparticles.
图 4 纳米La0.4Sr0.6B6粉末的(a) TEM照片、(b)单颗粒形貌照片、(c) HRTEM照片; (d)图(c)的傅里叶(FFT)变换; (e)—(g)所选择的单晶颗粒的La, Sr, B元素分布图
Fig. 4. (a) TEM image of La0.4Sr0.6B6 nanoparticles; (b) selected single crystal morphology; (c) HRTEM image for selected single crystal; (d) indexing FFT patterns from panel (c); (e)−(g) La , Sr , B element mapping for selected single crystal .
图 5 纳米La1–x Srx B6 (x = 0 (a), 0.2 (b), 0.4 (c), 0.6 (d), 0.8 (e))粉末的光学吸收曲线
Fig. 5. Optical absorption spectrum of La1–x Srx B6 (x = 0 (a), 0.2 (b), 0.4 (c), 0.6 (d), 0.8 (e)) nanoparticles.
图 6 La0.875Sr0.125B6晶体的态密度的第一性原理计算结果
Fig. 6. First-principle calculation results of density of states of La0.875Sr0.125B6 crystal.
图 7 La0.875Sr0.125B6晶体的(a)介电函数和(b)能量损失谱
Fig. 7. (a) Dielectric function and (b) loss function spectra of La0.875Sr0.125B6 crystal.
图 8 单晶SrB6的(a) (100)面、(b) (110)面、(c) (111)面、(d) (210)面的结构示意图及逸出功计算结果; (e) SrB6多晶块体的热电子发射电流密度随外加电压变化曲线; (f) SrB6多晶块体的lgJ-U 0.5曲线
Fig. 8. Schematic diagram of (a) (100) surface, (b) (110) surface, (c) (111) surface, (d) (210) surface of single crystal SrB6 and the calculated results of escape work; (e) thermionic emission current density of SrB6 polycrystalline bulk with applied voltage; (f) lgJ-U 0.5 curves of SrB6 polycrystalline bulk.
图 9 La1–x Srx B6多晶块体的热电子发射电流密度 (a) x = 0.8; (b) x = 0.6; (c) x = 0.4; (d) x = 0.2
Fig. 9. Thermionic emission current density of La1–x Srx B6 bulks: (a) x = 0.8; (b) x = 0.6; (c) x = 0.4; (d) x = 0.2.
图 10 La1–x Srx B6多晶块体肖特基外延曲线 (a) x = 0.8; (b) x = 0.6; (c) x = 0.4; (d) x = 0.2
Fig. 10. Typical Schottky plots for La1–x Srx B6 bulks: (a) x = 0.8; (b) x = 0.6; (c) x = 0.4; (d) x = 0.2.
图 11 所提出的La1–x Srx B6增强热电子发射机理示意图
Fig. 11. Proposed mechanism of the La1–x Srx B6 enhanced thermionic emission.
表 1 La1–x Srx B6 (x =1, 0.8, 0.6, 0.4, 0.2)多晶块体的零场发射电流密度J0和有效逸出功φe
Table 1. Zero field emission current density J0 and the effective escape work φe of the polycrystalline block La1–x Srx B6 (x = 1, 0.8, 0.6, 0.4, 0.2).
Compound 零场发射电流密度(J0) 有效逸出功
φe/
eV1673 K 1773 K SrB6 0.97 1.79 2.845 La0.2Sr0.8B6 1.67 4.73 2.691 La0.4Sr0.6B6 3.5 8.7 2.585 La0.6Sr0.4B6 4.1 8.3 2.573 La0.8Sr0.2B6 5.39 10 2.552 
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[1] Kirley M P, Novakovic B, Sule N, Weber M J, Knezevic I, Booske J H 2012 J. Appl. Phys. 111 063717
Google Scholar
[2] Xu J Q, Hou G H, Li H Q, Zhai T Y, Dong B P, Yan H L, Wang Y R, Yu B H, Bando Y, Golberg D 2013 NPG Asia Mater. 5 547
Google Scholar
[3] Kumari M, Gautam S, Shah P V, Pal S, Ojha U S, Kumar A, Naik A A, Rawat J S, Chaudhury P K, Harsh, Tandon R P 2012 Appl. Phys. Lett. 101 4995
Google Scholar
[4] Yuan Y F, Zhang L, HuLJ, Wang W, Min G H 2011 J. Solid State Chem. 184 3364
Google Scholar
[5] Tang H B, Su Y C, Tan J, Hu T, GongJY, Xiao L H 2014 Superattice Microst. 75 908
Google Scholar
[6] Chao L M, Bao L H, Wei W, Tegus O, Zhang Z D 2016 J. Alloys. Compd. 672 419
Google Scholar
[7] Mattox T M, Agrawal A, Milliron D J 2015 Chem. Mater. 27 6620
Google Scholar
[8] Chen M C, Lin Z W, Ling M H 2016 Acs Nano 10 93
Google Scholar
[9] Chen C J, Chen D H 2012 Chem. Eng. 180 337
Google Scholar
[10] Tang S L, Huang W C, Gao Y, An N, Wu Y D, Yang B, Yan M, Cao J Y, Guo C S 2021 J. Mater. Chem. B 9 4380
Google Scholar
[11] Takeda H, Kuno H, Adachi K 2008 J. Am. Ceram. Soc. 91 2897
Google Scholar
[12] Schelm S, Smith G B 2003 Appl. Phys. Lett. 82 4346
Google Scholar
[13] Adachi K, Miratsu M, Asahi T 2010 J. Mater. Res. 25 510
Google Scholar
[14] Schelm S, Smith G B, Grrett P D, Fisher W K 2005 J. Appl. Phys. 97 124314
Google Scholar
[15] Smith G B 2002 Mater. Forum. 26 20
[16] Bao L H, Qi X P, Ta N, Chao L M, Tegus O 2016 Phys. Chem. Chem. Phys. 18 19165
Google Scholar
[17] Bao L H, Chao L M, Wei W, Tegus O 2015 Mater. Lett. 139 187
Google Scholar
[18] Bao L H, Qi X P, Bao T N, Tegus O 2018 J. Alloy. Compd. 731 332
Google Scholar
[19] Zhou S L, Zhang J X, Bao L H, Yu X G, Hu Q L, Hu D Q 2014 J. Alloys. Compd. 611 130
Google Scholar
[20] Hasan M M, Cuskelly D, Sugo H, Kisi E H 2015 J. Alloy. Compd. 636 37
Google Scholar
[21] Hohenberg P, Kohn W 1964 Phys. Rev. 136 B864
[22] Vanderbilt D 1990 Phys. Rev. B 41 7892
Google Scholar
[23] Perdew J P, Burke K, Ernzerhof M 1996 Phys. Rev. Lett. 77 3865
Google Scholar
[24] Chao L M, Bao L H, Shi J J, Wei W, Tegus O, Zhang Z D 2015 J. Alloy. Compd. 622 618
Google Scholar
[25] Liu H L, Zhang X, Ning S Y 2017 Vacuum 143 245
Google Scholar
[26] Bao L H, Ming M, Tegus O 2015 J. Inorg. Mater. 30 1110
Google Scholar
[27] Xiao L H, Su Y C, Zhou X Z, Chen H Y, Tan J, Hu T, Yan J, Peng P 2012 Appl. Phys. Lett. 101 041913
Google Scholar
[28] Kimura S, Nanba T, Kunii S, Kasuya T 1990 Phys. Rev. B 59 3388
Google Scholar
[29] Kauer E 1963 Phys. Lett. 7 171
Google Scholar
[30] Kimura S, Nanba T, Kunii S, Suzuki T, Kasuya T 1990 Solid State Commun. 75 717
Google Scholar
[31] Bao L H, Qi X P, Ta N, Chao L M, Tegus O 2016 Cryst. Eng. Comm. 18 1223
Google Scholar
[32] Xin S W, Liu S C, Wang N, Han X Y, Wang L M, Xu B, Tian Y J, Liu Z Y, He J L, Yu D L 2011 J. Alloy. Compd. 509 7927
Google Scholar
[33] Zheng S, Zou Z, Min G, Yu H S, Han J D, Wang W T 2002 J. Mater. Sci. Lett. 21 313
Google Scholar
[34] Wang J, Zhu C, Meng F S, Liu G B, Gu Y, Wang H D, Gao S S, Wang K M 2018 Mod. Phys. Lett. B 32 1850007
Google Scholar
[35] Futamoto M, Nakazawa M, Kawabe U 1980 Surf. Sci 100 470
Google Scholar
[36] Swanson L W, Mcneely D R 1979 Surf. Sci 83 11
Google Scholar
[37] 周身林, 张久兴, 刘丹敏 2010 强激光与离子束 22 171
Google Scholar
Zhou S L, Zhang J X, Liu D M 2010 High Power Laser and Particle Beams 22 171
Google Scholar
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