Emission properties of compounds in the BaO · Sc 2O 3 · WO 3 ternary system

Abstract

It has been established that the addition of scandium in a variety of forms to thermionic cathodes, both oxide and dispenser types, results in a reduction of work function. The improved emission behavior has been found to be relatively short-lived, however, as ion bombardment causes a loss of the scandium necessary for the enhanced emission properties. While a variety of scandate cathode configurations have been investigated, several compounds have been observed to be common to the various types. The presence of one or more of these compounds appears to be necessary to establish the appropriate surface chemistry and structure. The eight binary compounds and one ternary compound determined to exist in the BaO · Sc 2O 3 · WO 3 ternary system have been evaluated with regard to work function and emission current density. Samples were evaluated with and without an ‘activating’ layer of BaO on the surface. Selected compounds were also mixed with 10 wt% tungsten and evaluated with and without a BaO layer. Finally the emission characteristics of the ternary compound, Ba 3Sc 2WO 9, were investigated as a function of tungsten content (5, 10, 20 and 30 wt%), both with and without a BaO layer on the surface. Comparisons are made between the various samples and data obtained from pure tungsten and Sc 2O 3 10 wt% W , both activated with BaO.