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/sup +/ and Cs/sup -/ can be separate species. On homogeneous surfaces, they can be treated as a resonance configuration of Cs/sub ad/. Stabilization of the work function /spl phi/(n/sub Cs/) when n/sub Cs/<10/sup 14/ cm/sup -2/ can be explained by the coexistence of Cs/sup +/ and Cs/sup -/ on the surface. Suppose, for example, that /spl phi/ decreases. In such a case, the concentration of Cs/sup -/ on the surface must increase and that of Cs/sup +/ decrease. Such processes lead to a net decrease in /spl phi/. To obtain a lower value of /spl phi/ it is necessary to have on or in the metal surface defects or impurity atoms which increase the adsorption energy of Cs/sup +/ or decrease the adsorption energy of Cs/sup $/.
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