Crystalline compounds found at the surface of model Ba-Sc-O-W thermionic cathodes (“scandate”) are uniquely identified using Raman spectroscopy. Thin films of sputtered BaO and Sc2O3 on W have been observed in thermionic emission microscopy, field emission scanning electron microscopy, optical microscopy, and Raman Spectroscopy. While the best thermionic electron emission is observed from areas that at the end of the cathode life are completely devoid of thin film BaO, Sc2O3 or observable bulk oxide or tungstate material, the poor emission areas are characterized by BaWO4, Ba2WO5 and long chain linear tungstates (νas = 860 cm−1) that are related to Scx-WOy components. There is no evidence from Raman spectroscopy that tetrahedral Sc2(WO4)3 is present or forms on the surface of the model cathode, or for the presence of Ba3WO6.

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