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The nanocrystal phases in a palladium-barium cathodes of the microwave devices

DOI 10.18127/j15604128-201805-03


V.I. Kapustin – Dr.Sc.(Phys.-Math.), Professor, Leading Specialist, Technical Center «Basic Technologies of EVD», JSC «Pluton» (Moscow); Professor, Department of Nanoelectronics, RTU MIREA (Moscow)
I.P. Li – Ph.D.(Eng.), Director, Technical Center «Basic Technologies of EVD», JSC «Pluton» (Moscow)
A.V. Shumanov – Deputy Director, Technical Center «Basic Technologies of EVD», JSC «Pluton» (Moscow)
S.O. Moskalenko – Bachelor, Process Engineer of the 1st category, Technical Center «Basic Technologies of EVD», JSC «Pluton» (Moscow)

Palladium-barium cathode materials are a composition of Pd powder and Pd5Ba intermetallide powder with a barium content in the composition of 0.5−2.0%. The emission properties and durability of Pd-Ba cathodes, as well as their resistance to electron bombard-ment, depend on the technological parameters of their manufacture and activation in the instruments. At present, the notion of a «film» mechanism for the operation of the Pd-Ba cathode is widespread. However, this model does not agree with the known experimental data on the regularities of the formation of the emission properties of such cathodes.
The aim of the work is to study the role of oxygen in the formation of the BaO phase, which is responsible for the emission properties of Pd-Ba cathodes, aimed at establishing the physical mechanism of the operation of palladium-barium cathodes. Therefore, in order to elucidate the mechanism of operation of such cathodes, the research tasks were: to study the dimensions and crystallographic orientation of Pd and Pd5Ba phase crystallites by X ray diffraction analysis of high resolution; investigation of the chemical state of bari-um and palladium in a cathode material by electron spectroscopy for chemical analysis (ESA).
The results of the investigations made it possible to formulate a «crystallite» model for the operation of Pd-Ba cathodes of microwave devices, which is fundamentally different from the known «film» model for the operation of such cathodes. The essence of the model is as follows: the components of Pd-Ba cathodes have a nanocrystallite structure, while the crystallite sizes along different crystallographic directions can vary greatly and depend on the technological background of materials; technological background determines the values of the parameters of the crystal structure of nanocrystallites, which also depend on the type and concentration of microimpurities dissolved in them; the diffusion mobility of microimpurities (C, O, H), as well as components of the cathode material (Ba, Pd), depending on the dimensions and lattice parameters of nanocrystallites along the crystallographic directions, determines the efficiency of the formation of new phases during the activation of the cathode, which, in their turn, determine its emission properties;
the emission properties of Pd-Ba cathodes determine the crystallites of the BaO(1−x) phase and Ba(1−y)O(1−x) Pdy phases containing oxygen vacancies and forming at the stage of cathode production and activation, while the «supplier» of oxygen for the production of crystalline data, Pd crystallites are predominantly those that have undergone arc melting as an excess phase in the synthesis of the Pd5Ba intermetallide, and the barium suppliers are the crystallites of the Pd5Ba phase.

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