This paper investigates the thermionic emission and adsorption properties of oxidized transition metals (Hf, Zr, Ti, and Nb) exposed to a flux of barium atoms. The surface cleanliness and oxidation kinetics were monitored using Auger electron spectroscopy under ultra-high vacuum conditions. The experimental findings reveal that despite similar initial work functions of the clean metals, their interaction with oxygen and barium is fundamentally governed by the substrate crystal lattice symmetry. In metals with a hexagonal close-packed (hcp) crystal lattice (Hf, Zr, Ti), three-dimensional interstitial suboxides are formed, where oxygen is strongly bound within the bulk lattice, resulting in weak barium adsorption on the surface. Consequently, the work functions of the Hf–O–Ba and Zr–O–Ba systems remain significantly high at 3.10–3.20 eV, thereby suppressing the thermionic emission current density by roughly 10⁴ times comparedtouncoateddispenser cathodes. In contrast, for body-centered cubic (bcc) niobium, oxygen localizes at the surface, increasing the dipole moment and markedly lowering the work function. Based on these insights, thin films of hafnium and zirconium are recommended as highly efficient anti-emission coatings operating at 1100–1300 K.