Excellent Thermionic-emission Performances of (Ce1-xGdx)B6 with Ultra-low Work Functions

doi:10.15541/jim20150587

Abstract

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

CLC Number:

TQ174

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.

Figures/Tables 7

References 20

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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

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

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

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

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

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