Materials Characterization of Surface Phases in Scandate Cathodes

Electron-transparent lamellae were extracted from a pair of scandate cathodes, each one made from L-S or L-L powders, and then examined using transmission electron microscopy (TEM). A distribution of chemically distinct phases appeared on the surface of tungsten grains, as well as inside them. While Ba and Al coexist in the same oxide particles, Sc exists separately in its own oxide phase. No evidence was found for the presence of a semiconducting layer containing both Ba and Sc, although it was specifically sought.