Preparation, Performance, and Work Function Model of Impregnated Tungstate Cathodes

Abstract

In this paper, we report an impregnated type of tungstate dispenser cathode prepared by Ba5Sr(WO6)2. The direct-current (dc) and pulsed-current (pc) emission properties and their evaporation rates have been investigated compared with the traditional Ba-W dispenser cathodes. Experimental results show that the current densities of the impregnated tungstate cathodes are twice larger than that of a typical 6-1-2 aluminate cathode, e.g., the dc and pc emission densities of the tungstate cathode can reach up to 10.6 and 56.6 A/cm2 at $1050~^{\circ }\text{C}_{{\text {br}}}$ , respectively. The evaporation rate of the impregnated tungstate cathode is $2.02\times 10^{-{9}}\text{g}\cdot $ cm $^{-2}\cdot \text{s}^{-1}$ at $1050~^{\circ }\text{C}_{{\text {br}}}$ , which is only 54% as much as that of the aluminate cathode, as measured by a quartz crystal oscillating method. The work function model of the tungstate cathode was studied by ab initio density functional theory (DFT) calculation. It is found that free Ba is preferentially adsorbed on the hollow site of ZrO2-W (001), and on BaZrO3 (001) in a more stable way during operation, resulting from its fine emitting and evaporation characteristics.