Electron Emission Enhancement of a (W-Sc<sub>2</sub>O<sub>3</sub>)-Coated Impregnated Cathode by Oxidation of the Coated Thin Film

Yamamoto, Shigehiko; Taguchi, Sadanori; Watanabe, Isato; Sasaki, Susumu

doi:10.1143/jjap.27.1411

Cited by 17 publications

(8 citation statements)

References 6 publications

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“…Sc has a stronger affinity for O than does Ba, which means that Ba cannot reduce Sc 2 O 3 to Sc directly [ 9 ]. In a cathode study by Yamamoto et al [ 35 ], it was proposed that metallic Sc can be produced via a chemical reaction between Sc 2 W 3 O 12 and Ba, as described in Equation (1), which was based on their work on (W–Sc 2 O 3 )-coated [ 42 ] and (W–Sc 2 W 3 O 12 )-coated impregnated cathodes [ 35 ]. Sc 2 W 3 O 12 + 3Ba = 3BaWO 4 + 2Sc …”

Section: Discussionmentioning

confidence: 99%

Near-Surface Material Phases and Microstructure of Scandate Cathodes

et al. 2019

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Scandate cathodes that were fabricated using the liquid-solid process and that exhibited excellent emission performance were characterized using complementary state-of-the-art electron microscopy techniques. Sub-micron BaAl2O4 particles were observed on the surfaces and edges of tungsten particles, as seen in cross-section samples extracted from the scandate cathode surface regions. Although several BaAl2O4 particles were observed to surround smaller Sc2O3 nanoparticles, no chemical mixing of the two oxides was detected, and in fact the distinct oxide phases were separately verified by chemical analysis and also by 3D elemental tomography. Nanobeam electron diffraction confirmed that the crystal structure throughout W grains is body-centered cubic, indicating that they are metallic W and did not experience noticeable changes, even near the grain surfaces, as a result of the numerous complex chemical reactions that occur during cathode impregnation and activation. 3D reconstruction further revealed that internal Sc/Sc2O3 particles tend to exhibit a degree of correlated arrangement within a given W particle, rather than being distributed uniformly throughout. Moreover, the formation of Sc/Sc2O3 particles within W grains may arise from W surface roughening that occurs during the liquid-solid synthesis process.

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Section: Discussionmentioning

confidence: 99%

Near-Surface Material Phases and Microstructure of Scandate Cathodes

et al. 2019

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“…BaAl 2 O 4 + Ba (10) In this case, the equilibrium Ba partial pressure was found to vary as: Efforts have been made to apply the above approach to scandate cathodes, focusing on the hypothesis that free Sc plays a similar role to free Ba in generating surface dipoles [146]. Yamamoto et al [128], [192], [223] proposed that free Ba participated in generation of free Sc according to the reactions:…”

Section: A Formation and Transport Mechanisms Of Free Metallic Ba And Scmentioning

confidence: 99%

“…The applied Sccontaining coatings have also varied with respect to chemical composition. Initially, W+ScH 2 , W+Sc 2 O 3 , or W+Sc 2 W 3 O 12 were used [16], [27], [40], [128]. Additional compositions including mixtures with Re, e.g.…”

Section: A Fabricationmentioning

confidence: 99%

“…Other experimental studies have examined more generally the coverages, compositions, and atomic configurations of Ba, Sc and O on W that result in optimal scandate cathode performance. Yamamoto et al [108], [128], [192] reported that a monoatomic layer of Ba-Sc-O reduces the work function of impregnated cathodes initially coated with W-Sc 2 O 3 . This improvement in emission was hypothesized to originate with the oxidation of W-Sc 2 O 3 into Sc 2 W 3 O 12 , which reacts with Ba to form free Sc atoms.…”

Section: Semiconductor Modelmentioning

confidence: 99%

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A Review of Sc-containing "Scandate" Thermionic Cathodes

Seif¹,

Zhou²,

Liu³

et al. 2022

Preprint

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Although thermionic emission has been studied for more than 100 years, recent interest in novel electron devices for military and civilian use has led to a surge in demand for cathodes with enhanced emission properties (e.g. higher current density, more uniform emission, lower operating temperatures, or extended in-service longevity). Sc-containing "scandate" cathodes have been widely reported to exhibit superior emission properties compared to previous-generation thermionic cathodes, including oxide, B-, and M-type cathodes. Despite extensive study spanning several decades, the mechanism by which the addition of Sc enhances cathode emission remains ambiguous, and certain limitations -non-uniform emission, low reproducibility, inconsistent longevity -continue to prevent widespread commercial integration of scandate cathodes into electron devices. This review attempts to survey the literature to-date addressing the fabrication, structure, and properties of scandate cathodes, with particular attention to studies addressing the role of Sc in enhancing emission.

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“…In 2002, Sasaki [92] found that the electron emission of Sc-cathodes is governed by a certain amount of Sc according to experimental results. Free Sc and free Ba [93] could migrate to the surface of cathode, and the Ba-Sc-O monolayer was formed on the W grains and effectively reduced the work function during activation. On the other hand, Wright et al [94] developed a semiconductor model for oxide cathodes, and then Raju et al [95] made a further modification.…”

Section: Scandia-doped Dispenser (Sdd) Cathodementioning

confidence: 99%

A review on recent progress of thermionic cathode

et al. 2020

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As the performance of vacuum electron devices is essentially governed by the properties of their cathodes, developing efficient and durable thermionic cathode is necessary and highly desired to meet the boosting requirements of vacuum electron devices. This review summarized the progress made in the past decades with a detailed discussion on the occurred various thermionic cathodes and their features, and the understandings of the correlation between the emission properties and the composition, where structure and synthesis method are well illustrated. Furthermore, dispenser cathodes with novel structures and emission mechanism are highlighted to indicate the recent achievement in this area of research, and Sc-cathode is considered as a promising candidate for the next-generation vacuum electron devices due to the greatly improved efficiency. However, challenges still exist to meet the ever-growing demands of thermionic cathode with collaborative requirement of high performance, easy fabrication and inadequate reproducibility.

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Electron Emission Enhancement of a (W-Sc₂O₃)-Coated Impregnated Cathode by Oxidation of the Coated Thin Film

Abstract: A simple formula, based on the classical impulse approxlmation, is given for the cross section for electron detachment collisions between fast Hions and neutral atoms or molecules T h e utility of the formula IS demonstrated by comparisons of calculated and measured cross sections.

Cited by 17 publications

References 6 publications

Near-Surface Material Phases and Microstructure of Scandate Cathodes

Near-Surface Material Phases and Microstructure of Scandate Cathodes

A Review of Sc-containing "Scandate" Thermionic Cathodes

A review on recent progress of thermionic cathode

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Electron Emission Enhancement of a (W-Sc2O3)-Coated Impregnated Cathode by Oxidation of the Coated Thin Film

Abstract: A simple formula, based on the classical impulse approxlmation, is given for the cross section for electron detachment collisions between fast Hions and neutral atoms or molecules T h e utility of the formula IS demonstrated by comparisons of calculated and measured cross sections.

Cited by 17 publications

References 6 publications

Near-Surface Material Phases and Microstructure of Scandate Cathodes

Near-Surface Material Phases and Microstructure of Scandate Cathodes

A Review of Sc-containing "Scandate" Thermionic Cathodes

A review on recent progress of thermionic cathode

Contact Info

Product

Resources

About

Electron Emission Enhancement of a (W-Sc₂O₃)-Coated Impregnated Cathode by Oxidation of the Coated Thin Film