Thermionic emission properties of a single-crystal LaB6 cathode

Abstract

A new type of LaB6 cathode has been developed. It consists of a 〈001〉 oriented LaB6 single-crystal tip and a glassy carbon filament. The influence of gas pressure on the thermionic emission properties are investigated for O2, H2O, CH4, and H2. Evaporation rates and surface composition of the LaB6 cathode are also examined. Thermionic emission current decreased in all gases examined here, depending on cathode temperature and gas pressure. In O2 and H2O gas atmosphere, the cathode surface composition appears to change to La2O3 as gas pressure is increased. The evaporation rate of the LaB6 single crystals is represented by equation V=4×1014 exp [−(570×103/RT)] μm/h, for the temperature range between 1800 and 2200 K.