Synthesis, characterization and properties of nanostructured (LaxBa1−x)B6 cathode materials by liquid phase reactive spark plasma sintering

Rare earth hexaboride are excellent thermionic electron cathodes materials with low work function, high emission, high brightness, and a long working time. Light rare earth hexaboride have recently attracted increasing interest due to their applications in electron source of high brightness and longevity [1]. Among these hexaborides, LaB
6
was widely investigated for its superior properties. However, the low resistivity (14.2 µΩ cm [2]) of LaB
6
is a disadvantage which makes it unsuitable for the direct cathode application, because this increases the heating power. Moreover, the traditional hot sintering method for preparation of LaB6 causes coarse grains and low emission property, which is due to the long sintering time and high temperature. In this paper, we report a study on a liquid phase reactive spark plasma sintering method of fabricating the (La
x
Ba
1−x
)B
6
compound. Spark plasma sintering (SPS) is a useful method for rapid sintering ceramic nanopowders, and it is suitable for preparation of ultra-fine crystal materials. We substitute the La partly with Ba, and it can be expected that the substitution increases the resistivity. Furthermore, since the radius of Ba is bigger than that of Fe, the substitution can enlarge the lattice constant, and this will decrease the work function.