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Nowadays, the output power and lifetime of a single magnetron are far from the requirements of industrial applications. So the new materials and methods are urgently needed to enhance the output power and prolong the lifetime of the magnetron. As the heart of a magnetron, cathode, whose quality directly affects the output power and lifetime of the magnetron, plays an important role. In order to enhance the output power and prolong the lifetime of the high power magnetron, a method of doping rare earth oxide Y2O3 into transition metal oxide HfO2 is used to prepare Y2Hf2O7 ceramic cathode. The thermionic emission and lifetime characteristics of the Y2Hf2O7 cathode are measured. The results show that the cathode can provide 0.15, 0.2, 0.5, 1.1, 1.8, 2.5, 3.5 A/cm2 current density for the space charge limitation at 1300, 1350, 1400, 1450, 1500, 1550, 1600 ℃br under 300 V anode voltage, respectively. Absolute zero work function of the cathode is only 1.26 eV obtained by the Richardson line method. The effective work function of the cathode is 3.10, 3.15, 3.21, 3.26 eV obtained by the Richardson-Dushman formula at 1450, 1500, 1550, 1600 ℃br respectively. The lifetime of the cathode is more than 4000 h under an initial load of 0.5 A/cm2 at 1400 ℃br, the lifetime which is much longer than the 2000 h average life span for the 2450 MHz continuous wave magnetron cathode used in production. Finally, the molecular structure, surface microstructure, element composition and content of the Y2Hf2O7 ceramic cathode are analyzed by the X-ray diffraction, scanning electron microscope, energy dispersive spectrometer, Auger electron spectroscopy with argon ion etching respectively. The analysis results show that the single Y2Hf2O7 phase forms under the high sintering temperature. When the Y3+ valence Y2O3 is doped into the Hf4+ valence HfO2, the substitutional solid solution will form. An oxygen vacancy is generated in the lattice, thus maintaining the electrical neutrality of the Y2Hf2O7 lattice. During the cathode activating, aging, and thermally testing, the oxygen vacancy is generated fast. The more the obtained oxygen vacancies, the higher the conductivity of the cathode surface will be. Besides, due to the improvement of the electro-conductivity thus enhancing the thermionic emission capability of the cathode, the work function of the cathode can be reduced.
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Keywords:
- magnetron /
- cathode /
- thermionic emission /
- lifetime /
- emission mechanism
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Chang T J, Qi X 1999 Modern Analysis Methods of Materials (Harbin: Harbin Institute of Technology Press) pp124, 125
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图 1 磁控管用新型铪酸钇陶瓷阴极剖面结构示意图
Figure 1. Section schematic of the Y2Hf2O7 ceramic cathode.
图 2 铪酸钇陶瓷阴极热发射测试装置示意图
Figure 2. Schematic of the thermionic emission testing system for the Y2Hf2O7 ceramic cathode.
图 3 直流发射电流密度随阳极电压变化曲线
Figure 3. I-V curves of the Y2Hf2O7 ceramic cathode.
图 4 阴极寿命特性曲线
Figure 4. Lifetime curve of the Y2Hf2O7 ceramic cathode.
图 5 铪酸钇陶瓷阴极
$\lg {j_{\rm{e}}} \text{-} \sqrt {{U_{\rm{a}}}} $ 曲线Figure 5.
$\lg {j_{\rm{e}}} \text{-} \sqrt {{U_{\rm{a}}}} $ curves of the Y2Hf2O7 ceramic cathode
图 6 铪酸钇陶瓷阴极理查森直线
Figure 6. Richardson curves of the Y2Hf2O7 ceramic cathode.
图 7 电子发射活性物质SEM微观结构形貌图
Figure 7. SEM image of the active substance.
图 8 电子发射活性物质EDS谱图及含量
Figure 8. EDS spectrum and element content of the active substance.
图 9 电子发射活性物质XRD谱图
Figure 9. XRD spectrum of the active substance.
图 10 铪酸钇陶瓷阴极表面SEM微观结构形貌图
Figure 10. SEM image of the Y2Hf2O7 ceramiccathode.
图 11 铪酸钇陶瓷阴极表面EDS谱图及含量
Figure 11. EDS spectrum and element content the cathode.
图 12 铪酸钇陶瓷阴极表面AES谱图
Figure 12. AES spectrum the Y2Hf2O7 ceramic cathode.
图 13 不同元素含量随阴极表面深度的变化曲线 (a) O元素; (b) Y和Hf元素
Figure 13. Element content as a function of the depth from the cathode surface: (a) O element; (b) Y and Hf element.
图 14 铪酸钇陶瓷阴极表面能带示意图
Figure 14. Energy band diagram of the Y2Hf2O7 ceramic cathode.
表 1 O, Y, Hf, C元素原子百分数与氩离子蚀刻深度的关系
Table 1. O, Y, Hf, C element content as a function of the depth using argon ion etching method.
Depth/nm Element content/at% O Y Hf C 0 47.5 21.7 13.9 17.0 3 44.2 21.8 15.0 19.0 5 36.0 20.2 20.9 22.9 10 36.1 23.0 20.0 20.9 35 31.3 32.3 23.3 13.4 100 50.0 18.0 19.4 12.5 200 49.3 23.8 18.2 8.7 500 43.0 24.5 21.9 10.6 
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[1] Jacqueline M R B, Paré J R J 2007 J. Microwave Power EE. 42 24
[2] Lester E, Kingman S, Dodds C 2005 Fuel 84 423
Google Scholar
[3] 岳松, 张兆传, 高东平 2013 物理学报 62 178401
Google Scholar
Yue S, Zhang Z C, Gao D P 2013 Acta Phys. Sin. 62 178401
Google Scholar
[4] 杨宋寒, 刘友春, 袁正勇 2014 中国专利ZL 201410193925.2
Yang S H, Liu Y C, Yuan Z Y 2014 CN Patent ZL 201410193925.2
[5] Zhang E Q 1980 IEEETrans. Elec. Dev. 27 1280
Google Scholar
[6] 电子管设计手册编辑委员会 1979 磁控管设计手册 (北京: 国防工业出版社) 第193, 211, 420页
Electronic tube design handbook editorial Committee 1979 Magnetron Design Handbook (Beijing: National Defence Industry Press) pp193, 211, 420 (in Chinese)
[7] Li SG, Yan T C, Li F L, Yang J S, Shi W 2016 IEEE Trans. Plasma. Sci. 44 1386
Google Scholar
[8] Huang H P, Huang K M, Liu C J 2018 IEEE Microw Wirel Co. 28 509
Google Scholar
[9] Buxbaum C, Gessinger G 1978 US Patent 4083811
[10] Goebel D M, Hirooka Y, Campbell G A 1985 Rev. Sci. Instrum 56 1888
Google Scholar
[11] Frank B, Gartner G 1985 US Patent 4533852
[12] Tadashi S, Kiyosaki M 1990 JP Patent 59179754
[13] Rao G S, Dharmadhikari C V, Nigavekar A S 1989 J Vac Sci Technol 7 3269
Google Scholar
[14] Wang J S, Zhou M L, Ma S Y J, Zuo T Y 2006 J. Alloys Compd. 419 172
Google Scholar
[15] Zhang J X, Zhou M L, Zhou W Y, Wang J S, Nie Z R, Zuo T Y 2002 Trans: Nonferrous Met. Soc. China 12 43
[16] Nie Z R, Zuo T Y, Zhou M L, Wang Y M, Wang J S 2000 J. Rare Earth 18 110
Google Scholar
[17] Bruining D H 1954 Physics and Application of Secondary Electron Emission (Oxford: Pergamon Press LTD) p19
[18] 刘学悫 1980 阴极电子学 (北京: 科学出版社) 第95, 97, 149, 211页
Liu X Q 1980 Cathode Electronics (Beijing: Science Press) pp95, 149, 184, 211 (in Chinese)
[19] 漆世锴, 王小霞, 罗积润, 赵青兰, 李云, 2016 物理学报 65 057901
Google Scholar
Qi S K, Wang X X, Luo J R, Zhao Q L, Li Y 2016 Acta Phys. Sin. 65 057901
Google Scholar
[20] Qi S K, Wang X X, Luo J R, Zhao S K, Zhao Q L, Li Y, Zhang Q Proceedings of IVESC Saint-Petersburg, Russia, June 30–July 4, 2014 p18
[21] Qi S K, Wang X X, Luo J R, Hu M W, Li Y 2015 Proceedings of IRMMW-THz Hong Kong, China, August 23–28, 2015 p12
[22] 漆世锴, 王小霞, 罗积润, 赵青兰, 张琪, 李云 2018 稀有金属材料与工程 473 784
Qi S K, Wang X X, Luo J R, Zhao S K, Zhao Q L, Li Y, Zhang Q 2018 Rare Metal Mat. Eng. 473 784
[23] 漆世锴, 王小霞, 罗积润, 胡明玮, 李云 2016 无机材料学报 31 987
Google Scholar
Qi S K, Wang X X, Luo J R, Hu M W, Li Y 2016 J. Inorg. Mater. 31 987
Google Scholar
[24] Hu M W, Wang X X, Qi S K 2019 IEEE Trans. Elec. Dev. 66 3592
Google Scholar
[25] Wang X X, Liao X H, Luo J R, Zhao Q L, Zhang M, Wang Q F, Li Y 2012 IEEETrans. Elec. Dev. 59 491
[26] 常铁军, 祁欣 1999 材料近代分析测试方法 (哈尔滨: 哈尔滨工业大学出版社) 第124, 125页
Chang T J, Qi X 1999 Modern Analysis Methods of Materials (Harbin: Harbin Institute of Technology Press) pp124, 125
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