Электронная структура вариантов составов скандатных и оксидно-никелевых катодов СВЧ приборов

By methods of electron spectroscopy for chemical analysis and spectroscopy of characteristic losses of electron energy, the electronic structure of barium oxide crystallites doped with other chemical elements, including scandium from scandium-containing phases, was investigated. The physical and physicochemical conditions are formulated, the fulfillment of which allows to form the electronic structure of the scandate cathode with a high level of thermionic emission: the achievement of the minimum ratio of the surface volume concentration of oxygen vacancies and the maximum distance between the top of the valence band and the Fermi level.

Desorption from Hot Scandate Cathodes: Effects on Vacuum Device Interior Surfaces after Long-Term Operation

Scandate cathodes have exhibited superior emission properties compared to current state-of-the-art “M-type” thermionic cathodes. However, their integration into vacuum devices is limited in part by a lack of knowledge regarding their functional lifespan and behavior during operation. Here, we consider thermal desorption from scandate cathodes by examining the distribution of material deposited on interior surfaces of a sealed vacuum device after ~26,000 h of cathode operation. XPS, EDS, and TEM analyses indicate that on the order of 1 wt.% of the initial impregnate is desorbed during a cathode’s lifetime, Ca does not desorb uniformly with time, and little to no Sc desorbs from the cathode surfaces (or does so at an undetectable rate). Findings from this first-ever study of a scandate cathode after extremely long-time operation yield insight into the utility of scandate cathodes as components in vacuum devices and suggest possible effects on device performance due to deposition of desorption products on interior device surfaces.

Study on Low-Temperature Emission Performance of Scandate Cathode with Micro-Blade-Type Arrays

In order to meet the requirements of high-frequency vacuum electronic devices with small size, high current density, and low working temperature, a kind of porous tungsten scandate cathode with micro-blade-type arrays was developed. The micro-blade-type arrays were fabricated by laser engraving technology. Subsequently, the cathode was prepared by a vacuum copper removal process and impregnated with active substances at high temperature. Experimental results show that the cathode exhibits excellent low-temperature electron emission performance and that the maximum pulse electron emission current density reaches 81.18 A/cm2 at 800 °C. The cathode also shows apparent combined thermal-field emission characteristics. Further analysis shows that a high electric field strength plays an important role in the electron emission of the scandate cathode. By virtue of the electric field enhancement effect formed by the fabricated micro-blade-type arrays on the cathode surface, the prepared cathode achieves high electron emission capacity.

Near-Surface Material Phases and Microstructure of Scandate Cathodes

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.