The minimum collector work function and the possibility of the existence of negative Cs ions on the collector surface [thermionic conversion]

Negative alkali metal ions are observed in some condensed phases; for example, ammonia solutions, tungsten bronzes, etc. Therefore, one cannot exclude them from the set of basis functions for alkali metals adsorbed on the electrode surfaces in thermionic converters. On inhomogeneous surfaces, Cs⁺ and Cs^- can be separate species. On homogeneous surfaces, they can be treated as a resonance configuration of Cs_ad. Stabilization of the work function φ(n_Cs) when n_Cs>10¹⁴ cm ^-2 can be explained by the coexistence of Cs⁺ and Cs^- on the surface. Suppose, for example, that φ decreases. In such a case, the concentration of Cs^- on the surface must increase and that of Cs⁺ decrease. Such processes lead to a net decrease in φ. To obtain a lower value of φ it is necessary to have on or in the metal surface defects or impurity atoms which increase the adsorption energy of Cs⁺ or decrease the adsorption energy of Cs^$