Effect of Sc<sub>2</sub>O<sub>3</sub> doping on thermal emission properties of rare-earth refractory yttrium salt cathode

QI Shikai; WANG Xingqi; LI Yun; ZHANG Qi; WANG Yu

doi:10.7498/aps.74.20250520

Abstract

To improve the thermionic emission performance of the rare-earth refractory yttrium salt cathode used in the magnetron, the influence of Sc₂O₃ doping on its thermionic emission properties is investigated. Cathodes are fabricated by incorporating different weight percentages of Sc₂O₃ into the rare-earth refractory yttrium salt matrix, and their thermionic emission properties are systematically evaluated. The experimental findings reveal that the doping of Sc₂O₃ significantly enhances the thermionic emission capability of the cathode. Notably, Sc₂O₃ with a doping concentration of 3% has the most significant improvement in emission performance. The 3% Sc₂O₃-doped cathode can achieve a thermionic emission current density of 3.85 A/cm² under an anode voltage of 300 V at 1600 ℃. In contrast, under the same conditions, the undoped cathode provides a current density of only 1.66 A/cm², indicating a 132% increase in thermionic emission efficiency when doped with 3% Sc₂O₃. By using the Richardson line method coupled with data-fitting algorithms, the absolute zero work functions for undoped and Sc₂O₃-doped cathodes (3%, 7%, and 11%) are determined to be 1.42, 0.93, 0.98, and 1.11 eV, respectively. The lifespan assessment indicates that at 1400℃ the cathode doped with 3% Sc₂O₃ remains stable for over 4200 h under an initial load of 0.5 A/cm² without significant degradation. Finally, those cathodes are analyzed by the XRD, SEM, EDS, AES respectively. The analyses show that during thermionic emission testing, the Sc₂O₃ and Y₂Hf₂O₇ undergo substitutional solid solution reactions, forming the Sc_xY_(2–x)Hf₂O_[7+(3/2)x] solid solution. This process causes lattice distortion in the Y₂Hf₂O₇, which makes it in a high-energy state, thus reducing the work function on the cathode surface. At the same time, Sc from Sc₂O₃ displaces Y in the Y₂Hf₂O₇ unit cells, with the displaced Y existing in the form of metal, which enhances the electrical conductivity of the cathode surface. Additionally, the Sc_xY_(2–x)Hf₂O_[7+(3/2)x] solid solution generates a substantial number of Vo²⁺ oxygen vacancies and free electrons, thereby further augmenting surface conductivity. All in all, these mechanisms contribute to significantly improving the thermionic emission capability of the cathode.

Keywords:

Authors and contacts

1.
School of Electronic and Information Engineering, Jiujiang University, Jiujiang 332005, China
2.
Jiangxi Provincial Key Laboratory of Material Surface Engineering, Jiujiang University, Jiujiang 332005, China
3.
Key Laboratory of High-Power Microwave Sources and Technologies, Aerospace Information Innovation Research Institute, Chinese Academy of Sciences, Beijing 100094, China

Corresponding author: QI Shikai, kaishiqi@126.com

Funds: Project supported by the National Natural Science Foundation of China (Grant No. 62161014) and the Key Laboratory of Material Surface Engineering of Jiangxi Province, China (Grant No. 2024SSY05072).

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References

[1]	Vyas S K, Verma R K, Maurya S 2016 Frequenz 70 455 Google Scholar
[2]	Patibandla A, Dobbidi P, Tiwari T 2023 24th International Vacuum Electronics Conference (IVEC) Chengdu, China, April 25–28, 2023 p1
[3]	Lim H, Jeong D H, Lee M, Ro S C 2017 IEEE Trans. Plasma. Sci. 45 2734 Google Scholar
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[5]	Timofeev N A, Sukhomlinov V S, Georges Z 2021 IEEE Trans. Plasma Sci. 49 2387 Google Scholar
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[11]	Wang X X, Meng M F, Zhang R Q, Li Y, Zhang Q 2023 IEEE Proceedings of IVEC Chengdu, China, April 25-28, 2023 p1145
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[13]	Zhang R Q, Wang X X, Ren F, Yin S Y 2024 IEEE Trans. Elec. Dev. 71 2078 Google Scholar
[14]	Zhang R Q, Ding S X, Wang X X, Ren F, Yin S Y 2025 IEEE Trans. Elec. Dev. 72 1427 Google Scholar
[15]	Mujan N S, Zhou Q F, Liu X T, John B, Matthew J B 2022 IEEE Trans. Elec. Dev. 69 3513 Google Scholar
[16]	Wang J S, Dong L R, Liu W, Yang F 2017 Sci. China Technol. Sc. 60 1439 Google Scholar
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[18]	Yang F, Wang J S, Liu W, Zhou M L 2015 Mater. Chem. Phys. 149–150 288 Google Scholar
[19]	Wang X Q, Wang X X, Luo J R, Qi S K, Li Y 2023 IEEE Trans. Elec. Dev. 70 2883 Google Scholar
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Cited By

图 1 阴极的剖面结构示意图

Figure 1. Cross-sectional structure schematic of the cathode.

DownLoad: Full-Size Img PowerPoint

图 2 不同质量分数Sc₂O₃掺杂稀土难熔钇盐阴极的伏安特性曲线　(a) 未掺杂Sc₂O₃; (b) 3% Sc₂O₃掺杂; (c) 7% Sc₂O₃掺杂; (d) 11% Sc₂O₃掺杂

Figure 2. I -V curves of the Sc₂O₃ doped rare-earth refractory yttrium salt cathodes: (a) Undoped Sc₂O₃; (b) 3% Sc₂O₃; (c) 7% Sc₂O₃; (d) 11% Sc₂O₃.

DownLoad: Full-Size Img PowerPoint

图 3 3% Sc₂O₃掺杂阴极实验寿命曲线

Figure 3. Lifetime curve of the 3% Sc₂O₃ doped cathode.

DownLoad: Full-Size Img PowerPoint

图 4 阴极的lg j -U ^1/2曲线　(a) 未掺杂Sc₂O₃; (b) 3% Sc₂O₃掺杂

Figure 4. lg j -U ^1/2 curves of the cathode: (a) Undoped Sc₂O₃; (b) 3% Sc₂O₃.

DownLoad: Full-Size Img PowerPoint

图 5 阴极的Richardson直线　(a) 未掺杂Sc₂O₃; (b) 3% Sc₂O₃掺杂

Figure 5. Richardson line of the cathode: (a) Undoped Sc₂O₃; (b) 3% Sc₂O₃.

DownLoad: Full-Size Img PowerPoint

图 6 未掺杂Sc₂O₃阴极活性物质表面SEM及XRD图　(a) SEM形貌; (b) XRD谱

Figure 6. SEM and XRD of the active material’s surface for the undoped Sc₂O₃: (a) SEM; (b) XRD.

DownLoad: Full-Size Img PowerPoint

图 7 阴极表面SEM形貌图　(a) 未掺杂Sc₂O₃; (b) 3% Sc₂O₃掺杂; (c) 7% Sc₂O₃掺杂; (d) 11% Sc₂O₃掺杂

Figure 7. SEM morphology of the cathode’s surface: (a) Undoped Sc₂O₃; (b) 3% Sc₂O₃; (c) 7% Sc₂O₃; (d) 11% Sc₂O₃.

DownLoad: Full-Size Img PowerPoint

图 8 阴极顶表面AES谱图

Figure 8. AES spectrum of the topmost layer on the cathode’s surface.

DownLoad: Full-Size Img PowerPoint

图 9 元素含量与氩离子蚀刻深度之间的关系

Figure 9. Elements content as a function of the depth using argon ion etching method.

DownLoad: Full-Size Img PowerPoint

图 10 晶胞结构示意图　(a) 未掺杂Sc₂O₃; (b) 掺杂Sc₂O₃

Figure 10. Schematic diagram of unit cell structure: (a) Undoped Sc₂O₃; (b) doped Sc₂O₃.

DownLoad: Full-Size Img PowerPoint

表 1 未掺杂、3%、7%、11% Sc₂O₃掺杂阴极表面元素成分及其原子百分比

Table 1. Element contents of the undoped, 3%, 7%, 11% Sc₂O₃ doped cathode and their atomic percentage.

Cathode type	Element type/%
Cathode type	Sc	Y	Hf	O
Undoped Sc₂O₃	0	19.88	25.23	54.89
3% Sc₂O₃ doped	0	22.03	26.35	51.62
7% Sc₂O₃ doped	6.37	16.99	18.25	58.39
11% Sc₂O₃ doped	15.10	12.81	18.98	53.11

DownLoad: CSV

表 2 O, Y, Hf, Sc, C元素原子百分比与氩离子蚀刻深度的关系

Table 2. O, Y, Hf, Sc, C atomic percentage as a function of the depth using argon ion etching method

Depth/nm	O/%	Y/%	Hf/%	Sc/%	C/%
0	31.1	22.3	15.6	3.8	27.2
5	22.5	33.5	20.0	3.2	20.8
10	31.4	30.0	17.4	2.5	18.7
20	34.2	24.7	19.0	3.2	18.9
50	37.6	21.4	17.7	4.3	19.0
100	46.3	17.5	14.8	4.8	16.6
200	54.9	15.8	14.4	4.7	10.2
300	52.8	15.0	14.2	5.2	12.8

DownLoad: CSV

[1]	Vyas S K, Verma R K, Maurya S 2016 Frequenz 70 455 Google Scholar
[2]	Patibandla A, Dobbidi P, Tiwari T 2023 24th International Vacuum Electronics Conference (IVEC) Chengdu, China, April 25–28, 2023 p1
[3]	Lim H, Jeong D H, Lee M, Ro S C 2017 IEEE Trans. Plasma. Sci. 45 2734 Google Scholar
[4]	Shang J H, Yang X Y, Wang Z Y, Hu M Y, Han C L, Zhang J X 2020 IEEE Trans. Elec. Dev. 67 2580 Google Scholar
[5]	Timofeev N A, Sukhomlinov V S, Georges Z 2021 IEEE Trans. Plasma Sci. 49 2387 Google Scholar
[6]	Bergner A, Scharf F H, Kühn G, Ruhrmann C, Hoebing T, Awakowicz P, Mentel J 2014 Plasma Sources Sci. T. 23 054005 Google Scholar
[7]	Makarov A P, Zemchikhin E M 2019 IEEE Proceedings of IVEC Busan, Korea (South), April 28–May 1, 2019 p112
[8]	Djubua B C, Polivnikova O V 2003 Appl. Surf. Sci. 215 242 Google Scholar
[9]	Djubua B C, Kultashev O K, Kultashev A P, Polivnikova O V 2012 IEEE Proceedings of IVESC Monterey, CA, USA, April 24–26, 2012 p185
[10]	Hu M W, Wang X X, Qi S K 2019 IEEE Trans. Elec. Dev. 66 3592 Google Scholar
[11]	Wang X X, Meng M F, Zhang R Q, Li Y, Zhang Q 2023 IEEE Proceedings of IVEC Chengdu, China, April 25-28, 2023 p1145
[12]	Wang X X, Liu Y W, Luo J R, Zhan Q L, Li Y, Zhang Q 2014 IEEE Trans. Elec. Dev. 61 605 Google Scholar
[13]	Zhang R Q, Wang X X, Ren F, Yin S Y 2024 IEEE Trans. Elec. Dev. 71 2078 Google Scholar
[14]	Zhang R Q, Ding S X, Wang X X, Ren F, Yin S Y 2025 IEEE Trans. Elec. Dev. 72 1427 Google Scholar
[15]	Mujan N S, Zhou Q F, Liu X T, John B, Matthew J B 2022 IEEE Trans. Elec. Dev. 69 3513 Google Scholar
[16]	Wang J S, Dong L R, Liu W, Yang F 2017 Sci. China Technol. Sc. 60 1439 Google Scholar
[17]	Yang F, Wang J S, Liu W, Liu X, Zhou M L 2013 Appl Surface Sci. 270 746 Google Scholar
[18]	Yang F, Wang J S, Liu W, Zhou M L 2015 Mater. Chem. Phys. 149–150 288 Google Scholar
[19]	Wang X Q, Wang X X, Luo J R, Qi S K, Li Y 2023 IEEE Trans. Elec. Dev. 70 2883 Google Scholar
[20]	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
[21]	Sakharov K A, Simonenko E P, Simonenko N P 2018 Ceram. Int. 44 7647 Google Scholar
[22]	周宏明, 易丹青 2008 无机材料学报 23 247 Google Scholar Zhou H M, Yi D Q 2008 J. Inorg. Mater. 23 247 Google Scholar
[23]	袁志谦, 周增林, 李艳, 何学良, 陈文帅, 张婉婷 2024 材料导报 39 24100155 Yuan Z Q, Zhou Z L, Li Y, He X L, Chen W S, Zhang W T 2024 Materials Reports 39 24100155
[24]	Prashar G, Vasudev H, Thakur L 2023 Prot. Met. Phys. Chem. Surf. 59 461 Google Scholar
[25]	Wang J S, Chen M D, Li C Z, Chen L Y, Yu Y S, Wang Y H, Liu B, Jing Q S 2021 Surf. Coat. Technol. 428 127879 Google Scholar
[26]	Guo Y Q, Guo L, Liu K Y, Qiu S Y, Guo H B, Xu H B 2024 J. Mater. Sci. Technol. 182 33 Google Scholar

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Effect of Sc₂O₃ doping on thermal emission properties of rare-earth refractory yttrium salt cathode

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Effect of Sc2O3 doping on thermal emission properties of rare-earth refractory yttrium salt cathode

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Effect of Sc₂O₃ doping on thermal emission properties of rare-earth refractory yttrium salt cathode