Characterization of the Materials, Phases and Morphology Typical of High-Performance Scandate Cathodes

Scandate cathodes offer the promise, and in some cases, they exhibit demonstrated capabilities, of next-generation electron emitters suitable for high-performance electron guns. However, there remains a knowledge gap related to the materials and microstructure that might be targeted in order to consistently produce scandate cathodes that reliably deliver excellent emission properties. This paper will provide an overview of a multi-year project focused on characterization of the materials, phases and microstructures observed for scandate cathodes that had performed well during close-spaced diode testing. Typical features include highly faceted tungsten grains, the presence of nanoscale barium-containing particles that decorate the surfaces of tungsten grains, and the presence of scandium at the cathode's emitting surface. Additional insights into scandate cathode materials were obtained via large-area mapping of the distribution of elements and phases through the thickness of impregnated and life-tested cathode pellets.