低逸出功Ce1-xGdxB6单晶体的制备及其热发射性能

doi:10.15541/jim20150587

无机材料学报 ›› 2016, Vol. 31 ›› Issue (8): 797-801.DOI: 10.15541/jim20150587

低逸出功Ce_1-_xGd_xB₆单晶体的制备及其热发射性能

王杨¹, 张忻¹, 张久兴^{1, 2}, 刘洪亮¹, 江浩¹, 李录录¹

(1. 北京工业大学材料科学与工程学院, 新型功能材料教育部重点实验室, 北京 100124; 2. 合肥工业大学材料科学与工程学院, 合肥 230009)

收稿日期:2015-11-30 修回日期:2016-01-30 出版日期:2016-08-20 网络出版日期:2016-07-20
作者简介:王杨(1988–), 女, 硕士研究生. E-mail: wangyang132@emails.bjut.edu.cn
基金资助:
国家自然科学基金(51371010);北京市教育委员会科技计划面上项目(KM201510005001)

Excellent Thermionic-emission Performances of (Ce_1-_xGd_x)B₆ with Ultra-low Work Functions

WANG Yang¹, ZHANG Xin¹, ZHANG Jiu-Xing^{1, 2} , LIU Hong-Liang¹, JIANG Hao¹, LI Lu-Lu¹

(1. College of Materials Science and Engineering, Beijing University of Technology, Key Laboratory of Advanced Functional Materials, Ministry of Education, Beijing 100124, China; 2. School of Materials Science and Engineering, Hefei University of Technology, Hefei 230009, China)

Received:2015-11-30 Revised:2016-01-30 Published:2016-08-20 Online:2016-07-20
About author:WANG Yang. wangyang132@emails.bjut.edu.cn
Supported by:
National Natural Science Foundation of China (51371010);Beijing Education Commission Project on Science and Technology (KM201510005001)

摘要/Abstract

摘要：

以三元稀土硼化物Ce_1-_xGd_xB₆为研究对象, 系统研究Gd掺杂对CeB₆阴极材料热发射性能的影响规律。采用放电等离子烧结结合光学区域熔炼法成功制备了高质量的Ce_1-_xGd_xB₆(x=0~0.3)单晶体。借助360度Phi扫描单晶衍射仪对生长后的单晶进行了测试, 结果显示单晶质量良好。采用劳埃定向仪确定出(100)晶面, 并测试了该晶面在1673 K、1773 K、1873 K下的热电子发射电流密度。测试结果表明, Ce_0.9Gd_0.1B₆成分单晶体具有最优异的热发射性能, 在1873 K工作温度下, 4000 V电压条件下发射电流密度达到82.3 A/cm², 零场电流发射密度为24.70 A/cm², 平均有效逸出功为2.30 eV, 与相同条件下CeB₆单晶体热发射性能(热发射电流密度为78.2 A/cm², 零场电流发射密度为13.32 A/cm²)相比, 其具有更大的发射电流密度和更低的逸出功。因此, 采用该制备技术获得的Ce_1-_xGd_xB₆单晶体具有良好的发射性能, 作为热阴极材料将会有更好的应用前景。

关键词: 光学区域熔炼法, Ce1-xGdxB6单晶体, 热发射性能

Abstract:

CeB₆ with simple cubic CaB₆-type structure has attracted much interest owing to its promising scientific and technological characteristics like high brightness, high melting point, low vapor pressure, long service life, and low work function. High-quality Ce_1-_xGd_xB₆(x=0~0.3) single crystals with ultra-low work function are successfully synthesized via the spark plasma sintering combining floating zone technique. The quality, chemical composition and thermionic emission properties of the Ce_1-_xGd_xB₆ single crystals were systematically investigated by 360° phi scanning X-ray single crystal diffraction, X-ray fluorescence and emission measurements. Based on the testing results, the prepared single crystals exhibit good quality. The emission current density of Ce_0.9Gd_0.1B₆on (100) crystal surface is up to 82.3 A/cm² higher than that of CeB₆ under 4000 V at 1873 K, while the current density under zero voltage condition is 24.70 A/cm², about two-fold higher than that of CeB₆. The average value of effective work functions at different temperatures is reduced to 2.30 eV lower than 2.93 eV of CeB₆. Such excellent performances suggest that the ternary hexaborides can be used as a promising cathode emitter source for exploration and research in the electron emitter field.

Key words: floating zone method, (Ce1-xGdx)B6 single crystal, thermionic emission property

中图分类号:

TQ174

王杨, 张忻, 张久兴, 刘洪亮, 江浩, 李录录. 低逸出功Ce_1-_xGd_xB₆单晶体的制备及其热发射性能[J]. 无机材料学报, 2016, 31(8): 797-801.

WANG Yang, ZHANG Xin, ZHANG Jiu-Xing,LIU Hong-Liang, JIANG Hao, LI Lu-Lu. Excellent Thermionic-emission Performances of (Ce_1-_xGd_x)B₆ with Ultra-low Work Functions[J]. Journal of Inorganic Materials, 2016, 31(8): 797-801.

图/表 7

图1 Ce0.9Gd0.1B6单晶的实物照片

Fig. 1 Photograph of Ce0.9Gd0.1B6 single crystal

图2 Ce0.9Gd0.1B6单晶的断口SEM照片

Fig. 2 Fracture SEM image of Ce0.9Gd0.1B6 single crystal

图3 二次区熔Ce0.95Gd0.05B6晶体的衍射图谱

Fig. 3 Diffraction photographs of second zone melting crystal Ce0.95Gd0.05B6 (a) 360° rapid scanning; (b) slow scanning alone the [001] direction

图4 (a) Ce0.95Gd0.05B6单晶切割后的(100)晶面劳埃照片和 (b) Ce0.95Gd0.05B6单晶摇摆曲线

Fig. 4 (a) Laue pattern of cutting (100) plane and (b) rocking curves of Ce0.95Gd0.05B6 single crystal

图5 肖特基直线外延法计算Ce1-xGdxB6单晶体零场电流密度

Fig. 5 Calculate J0 of Ce1-xGdxB6 single crystal by method of Schottky line

表1 Ce1-xGdxB6单晶体的成分及物理性能

Table 1 Component and physical properties of the single crystal Ce1-xGdxB6

Theory component	Actual component	Lattice constant/nm	Vickers hardness/GPa	Ralative density/％
CeB₆	CeB₆	4.140	26.4	99.98
Ce_0.9Gd_0.1B₆	Ce_0.95Gd_0.05B₆	4.137	26.7	99.99
Ce_0.8Gd_0.2B₆	Ce_0.92Gd_0.08B₆	4.131	26.5	99.99
Ce_0.7Gd_0.3B₆	Ce_0.88Gd_0.12B₆	4.099	26.0	99.98

表2 ReB6单晶体(100)晶面的电流发射密度和平均有效逸出功

Table 2 Thermionic emission current density and average effective work functions of ReB6 single crystal (100) plane

Component	j₀/(A·cm^-2)			Average work function/eV	Reference
Component	1673 K	1773 K	1873 K	Average work function/eV	Reference
LaB₆	8.13	12.80	18.34	2.67	[13]
CeB₆	4.48	7.73	13.32	2.42	This work
PrB₆	2.56	7.79	11.16	2.74	—
GdB₆	5.28	6.33	7.58	2.45	—
La_0.2Ce_0.8B₆	4.89	12.30	36.30	2.66	[19]
Ce_0.8Pr_0.2B₆	6.28	18.36	24.55	2.61	[15]
Ce_0.95Gd_0.05B₆	12.69	17.53	24.70	2.30	This work
Ce_0.92Gd_0.08B₆	10.35	15.13	18.70	2.36	This work
Ce_0.88Gd_0.12B₆	7.12	10.42	14.42	2.37	This work

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低逸出功Ce_1-_xGd_xB₆单晶体的制备及其热发射性能

Excellent Thermionic-emission Performances of (Ce_1-_xGd_x)B₆ with Ultra-low Work Functions

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