<i>In Situ</i> Emission Microscopy of Scandium/Scandium-Oxide and Barium/Barium-Oxide Thin Films on Tungsten

Vaughn, Joel; Jamison, Keith; Kordesch, Martin E.

doi:10.1109/ted.2009.2015410

Cited by 34 publications

(16 citation statements)

References 13 publications

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“…This particular investigation is motivated by the recent results of experimental studies of electron emission from scandia-coated cathodes reported in Ref. 7. In Ref.…”

Section: Introductionmentioning

confidence: 99%

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Intrinsic defects and conduction characteristics of Sc2O3in thermionic cathode systems

2012

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Recent experimental observations indicate that bulk Sc 2 O 3 (~200 nm thick), an insulator at room temperature and pressure, must act as a good electronic conductor during thermionic cathode operation, leading to the observed high emitted current densities and overall superior emission properties over conventional thermionic emitters which do not contain Sc 2 O 3 . Here, we employ ab initio methods using both semilocal and hybrid functionals to calculate the intrinsic defect energetics of Sc and O vacancies and interstitials and their effects on the electronic properties of Sc 2 O 3 in an effort to explain the good conduction of Sc 2 O 3 observed in experiment. The defect energetics were used in an equilibrium defect model to calculate the concentrations of defects and their compensating electron and hole concentrations at equilibrium. Overall, our results indicate that the conductivity of Sc 2 O 3 solely due to the presence of intrinsic defects in the cathode operating environment is unlikely to be high enough to maintain the magnitude of emitted current densities obtained from experiment, and that presence of impurities are necessary to raise the conductivity of Sc 2 O 3 to a high enough value to explain the current densities observed in experiment. The necessary minimum impurity concentration to impart sufficient electronic conduction is very small (approximately 7.5x10 -3 ppm) and is probably present in all experiments.

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“…This particular investigation is motivated by the recent results of experimental studies of electron emission from scandia-coated cathodes reported in Ref. 7. In Ref.…”

Section: Introductionmentioning

confidence: 99%

“…In Ref. 7, Sc 2 O 3 was sputter deposited onto a polycrystalline W foil. BaO was subsequently deposited on top of some of the Sc 2 O 3 regions in a square pattern with a final film thickness on the order of a couple hundred nanometers.…”

Section: Introductionmentioning

confidence: 99%

Intrinsic defects and conduction characteristics of Sc2O3in thermionic cathode systems

2012

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“…There are many remarkable advantages of scandate cathode compared with the ''M'' type cathode, i.e., the working temperature of scandate cathode can be reduced by 100-150°C, which is highly significant in vacuum electronic devices. It was found in previous work that the raw powder properties, for example morphology and particle size, greatly affected the emission property of the cathode [2][3][4][5][6][7][8][9][10][11][12][13][14][15].…”

Section: Introductionmentioning

confidence: 99%

Preparation and characterization of scandia-doped tungsten powders prepared by a spray-drying method

2011

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Scandium oxide-doped tungsten powders were prepared by a new method of spray drying combined with two-step hydrogen reduction. The particle size of doped tungsten, powder morphology, and distribution of doped scandium oxide were characterized by scanning electron microscopy, X-ray diffraction, and laser diffraction particle size analysis. Experimental results indicated that the predecessor powders prepared by spray drying were spherical in shape. Two compounds, WO 3 and Sc 2 W 3 O 12 , in the raw powder calcined at 600°C were transformed into metallic tungsten and scandia after reduction at 850°C by hydrogen for 1 h. The scandia-doped tungsten powders obtained had an average size of 950 nm and scandium oxide was distributed evenly throughout the tungsten powder. The mechanism of reduction of the doped tungsten oxide is discussed in this paper.

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“…An increase of current density cathode at a given working temperature is a main trend in the development of thermionic cathode for different in vacuum devices. Among all the electron emitters, Scandate cathodes have aroused great attention among all the thermionic cathodes due to their high current density [4][5][6].In this paper, scandate doped pressed (SDP) cathodes were prepared by a new method of spray drying combined with two-step hydrogen reduction, instead of traditional mechanical mixing of scandium oxide and barium-calcium aluminates with tungsten. The microstructure, element distribution, and emission properties of the cathodes have been characterized by scanning electron microscope, energy dispersive spectrometer, and an emission test system, respectively.…”

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confidence: 99%

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confidence: 99%

High current density Scandate doped pressed cathode fabrication

Cui

Wang

Liu

et al. 2010

2010 8th International Vacuum Electron Sources Conference and Nanocarbon

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Vacuum electron apparatus has a wide application in civil and military field, such as communication, broadcastings and aviation industry [1][2][3]. An increase of current density cathode at a given working temperature is a main trend in the development of thermionic cathode for different in vacuum devices. Among all the electron emitters, Scandate cathodes have aroused great attention among all the thermionic cathodes due to their high current density [4][5][6].In this paper, scandate doped pressed (SDP) cathodes were prepared by a new method of spray drying combined with two-step hydrogen reduction, instead of traditional mechanical mixing of scandium oxide and barium-calcium aluminates with tungsten. The microstructure, element distribution, and emission properties of the cathodes have been characterized by scanning electron microscope, energy dispersive spectrometer, and an emission test system, respectively.The SEM image of SDP cathode and corresponding EDX results are shown in Fig.l. It can be seen that the cathode prepared by spray drying method have a smooth surface and good sub-micrometer quasi-spherical tungsten grain structure with homogeneous distribution of scandia and barium-calcium aluminates, which are dispersed over and among tungsten grains.The SEM image of cathode cross section and related EDX results [ F ig.2 (a) and (b)] also show that the cathode consists of sub-micrometer quasi-spherical tungsten grains with Sc and barium-calcium aluminate which exist at the interface of the tungsten grains. The sub-micrometer microstructure of cathode is favorable for the active substance diffusing from the inside to the cathode surface and improved the distribution homogeneity of scandia in tungsten Fig.l (a) SEM image of SOP cathode surface and (b) corresponding EOX results Fig.2 (b) SEM image of SOP cathode cross section and (b) corresponding EOX results 978-1-4244-6644-3/10/$26.00 ©2010 IEEE 168

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In Situ Emission Microscopy of Scandium/Scandium-Oxide and Barium/Barium-Oxide Thin Films on Tungsten

Cited by 34 publications

References 13 publications

Intrinsic defects and conduction characteristics of Sc2O3in thermionic cathode systems

Intrinsic defects and conduction characteristics of Sc2O3in thermionic cathode systems

Preparation and characterization of scandia-doped tungsten powders prepared by a spray-drying method

High current density Scandate doped pressed cathode fabrication

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