Thermionic emission behavior of rare-earth lanthanum hexaboride polycrystal and single crystal

IF 3.9 2区材料科学 Q2 MATERIALS SCIENCE, MULTIDISCIPLINARY Vacuum Pub Date : 2025-03-22 DOI:10.1016/j.vacuum.2025.114277

Zengjie Gu , Yanhui Jia , Hong Gao , Xinyu Yang

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Abstract

The spark plasma sintering and optical floating zone melting techniques were used to prepare the rare-earth lanthanum hexaboride (LaB₆) polycrystal and single crystal, respectively. LaB₆ polycrystal achieved a maximum relative density of 98.5 % and an average grain size of 11.65 ± 3.21 μm at T = 1950°C, P = 40 MPa and t = 13min. The corresponding highest thermionic current density was 10.13 A/cm². The surface height of the internal grain exceeded that of the grain boundaries, indicating a faster consumption rate at the grain boundaries due to their lower work functions. The LaB₆ [100] single crystal, characterized by a full width at half-maximum (FWHM) of 0.13°, exhibited the highest current density of 13.1 A/cm²achieved at 1673 K, surpassing that of the LaB₆ polycrystal measured at 1873 K. The height difference on the surface of the single crystal was significantly lower than that of the polycrystal, suggesting improved thermionic emission uniformity for LaB₆ [100] single crystal.

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稀土六硼化镧多晶和单晶的热离子发射行为

采用火花等离子烧结和光学浮区熔炼技术分别制备了稀土六硼化镧（LaB6）多晶和单晶。在温度为1950℃，温度为40 MPa，温度为13min时，LaB6多晶的最大相对密度为98.5%，平均晶粒尺寸为11.65±3.21 μm。相应的最高热离子电流密度为10.13 A/cm2。内部晶粒的表面高度超过晶界的表面高度，表明晶界处的消耗速度更快，因为它们的功函数更低。LaB6[100]单晶在1673 K时的电流密度最高，为13.1 a /cm2，超过了在1873 K时测得的LaB6多晶。单晶表面的高度差明显小于多晶表面的高度差，表明LaB6[100]单晶的热离子发射均匀性得到了改善。

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来源期刊

Vacuum 工程技术-材料科学：综合

CiteScore

6.80

自引率

17.50%

发文量

审稿时长

34 days

期刊介绍： Vacuum is an international rapid publications journal with a focus on short communication. All papers are peer-reviewed, with the review process for short communication geared towards very fast turnaround times. The journal also published full research papers, thematic issues and selected papers from leading conferences. A report in Vacuum should represent a major advance in an area that involves a controlled environment at pressures of one atmosphere or below. The scope of the journal includes: 1. Vacuum; original developments in vacuum pumping and instrumentation, vacuum measurement, vacuum gas dynamics, gas-surface interactions, surface treatment for UHV applications and low outgassing, vacuum melting, sintering, and vacuum metrology. Technology and solutions for large-scale facilities (e.g., particle accelerators and fusion devices). New instrumentation ( e.g., detectors and electron microscopes). 2. Plasma science; advances in PVD, CVD, plasma-assisted CVD, ion sources, deposition processes and analysis. 3. Surface science; surface engineering, surface chemistry, surface analysis, crystal growth, ion-surface interactions and etching, nanometer-scale processing, surface modification. 4. Materials science; novel functional or structural materials. Metals, ceramics, and polymers. Experiments, simulations, and modelling for understanding structure-property relationships. Thin films and coatings. Nanostructures and ion implantation.