Oxide cathodes. The effect of the coating-core interface on conductivity and emission

Abstract

In an oxide cathode a coating of Ba/Sr oxide is applied to a base consisting of nickel which may contain magnesium or aluminium. It is found that a potential barrier occurs at the interface leading to a rectifier action. This restricts the current flow when electrons pass from metal to coating. It is shown that in a well-aged and well-activated coating it is this restriction which determines not only the conduction current in the coating, but also the thermionic emission which can be drawn from it. The fact that the volt drop in the coating occurs primarily across a layer of thickness less than 10 -4 cm. has important consequences as regards breakdown and the shape of the characteristic beyond saturation. The rapid decay of emission immediately following application of anode voltage is also to be associated with the barrier.