Tungstate formation in a model scandate thermionic cathode

Wan, Congshang; Kordesch, Martin E.

doi:10.1116/1.4772007

Cited by 16 publications

(5 citation statements)

References 35 publications

(29 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The formation of Sc 2 W 3 O 12 is required since cathode activation/operating temperatures are not high enough to decompose Sc 2 O 3 directly [193], [194]. Other studies by Sasaki et al [21], Wan and Kordesch [195], and Liu 112) [99] et al [19] support the idea that free Sc atoms at the surface supplied by chemical reactions inside the W matrix form a surface monolayer consisting of Ba, Sc, and O. Additional discussion of plausible reactions for the production of free cations is included in the Appendix.…”

Section: Semiconductor Modelmentioning

confidence: 98%

A Review of Sc-containing "Scandate" Thermionic Cathodes

Seif¹,

Zhou²,

Liu³

et al. 2022

Preprint

View full text Add to dashboard Cite

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.

show abstract

Section: Semiconductor Modelmentioning

confidence: 98%

A Review of Sc-containing "Scandate" Thermionic Cathodes

Seif¹,

Zhou²,

Liu³

et al. 2022

Preprint

View full text Add to dashboard Cite

show abstract

“…This result that the emitted current density varies across different grains due to the difference in their work function values is consistent with experimental thermionic electron emission microscopy (ThEEM) images obtained in the TL region. [16,[18][19][20][21][22][23][24][25][26][27] As the schematic figures show, in the TL (Fig. 6a) and the transition region (Fig.…”

Section: Two-dimensional Emission Mapmentioning

confidence: 99%

“…[3,5,6,[14][15][16][17] The non-uniform nature of thermionic electron emission from polycrystalline W has been observed experimentally by using thermionic electron emission microscopy (ThEEM). [16,[18][19][20][21][22][23][24][25][26][27] In a representative ThEEM image, at a particular temperature, certain grains of the W surface are bright while others remain dark, indicating that some grains are more emissive than others, due to factors such as lower work function, surface topography, etc.…”

Section: Introductionmentioning

confidence: 99%

Physics-based Model for Nonuniform Thermionic Electron Emission from Polycrystalline Cathodes

Chen¹,

Jacobs²,

Petillo³

et al. 2021

Preprint

View full text Add to dashboard Cite

A new physics-based model is developed that predicts the emitted current from thermionic emission that accurately spans from the temperature-limited (TL) to the full-space-charge-limited (FSCL) regions. Experimental observations of thermionic electron emission demonstrate a smooth transition between TL and FSCL regions of the emitted-current-density-versus-temperature (J − T ) (Miram) curve and the emitted-current-density-versus-voltage (J − V ) curve. Knowledge of the temperature and shape of the TL-FSCL transition is important in evaluating the thermionic electron emission performance of cathodes, including predicting the lifetime. However, there have been no firstprinciples physics-based models that can predict the smooth TL-FSCL transition region for real thermionic cathodes without applying physically difficult to justify a priori assumptions or empirical phenomenological equations. Previous work detailing the nonuniform thermionic emission found that the effects of 3-D space charge, patch fields (electrostatic potential nonuniformity on the cathode surface based on local work function values), and Schottky barrier lowering can lead to a smooth TL-FSCL transition region from a model thermionic cathode surface with a checkerboard spatial distribution of work function values. In this work, we construct a physics-based nonuniform emission model for commercial dispenser cathodes for the first time. This emission model is obtained by incorporating the cathode surface grain orientation via electron backscatter diffraction (EBSD) and the facet-orientation-specific work function values from density functional theory (DFT) calculations. The model enables construction of two-dimensional emitted current density maps of the cathode surface and corresponding J − T and J − V curves. The predicted emission curves show excellent agreement with experiment, not only in TL and FSCL regions but, crucially, also in the TL-FSCL transition region. This model provides a method to predict the thermionic emission from the microstructure of a commercial cathode, and improves the understanding on the relationship between thermionic emission and cathode microstructure, which is beneficial to the design of vacuum electronic devices.

show abstract

“…Then researchers paid a lot of effort to increase the electron emission capability by controlling the introducing approaches of Sc and the microstructure of the obtained cathodes, and advanced strategies including the liquid-liquid (L-L) precipitation method, liquid-solid (L-S) precipitation method [73] and pulse laser deposition (PLD) technology [74] are developed to improve the distribution uniformity of the scandium oxide. Up to now, Sc-cathodes have been considered as one of the most potential candidates for the next generation cathodes with high current density [75][76][77], and could be divided into three different types [45]: the top-layer scandate cathode [72], impregnated scandate cathode (Sc 2 O 3 was mixed with Ba-Ca-aluminate impregnant) and scandia-doped dispenser (SDD) cathode [78].…”

Section: Sc-cathodementioning

confidence: 99%

A review on recent progress of thermionic cathode

et al. 2020

View full text Add to dashboard Cite

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.

show abstract

Tungstate formation in a model scandate thermionic cathode

Cited by 16 publications

References 35 publications

A Review of Sc-containing "Scandate" Thermionic Cathodes

A Review of Sc-containing "Scandate" Thermionic Cathodes

Physics-based Model for Nonuniform Thermionic Electron Emission from Polycrystalline Cathodes

A review on recent progress of thermionic cathode

Contact Info

Product

Resources

About