Internal Cation Mobilities in the Molten Systems (Li-Rb)N03 and (Li-Cs)NOs

The relative differences in internal cation mobilities are measured for the molten systems (Li—Rb)N03 and (Li—Cs)N03 over a wide range of temperatures and concentrations with a countercurrent electromigration method, and the internal mobilities are calculated from these results and the available data on the electrical conductivity. The following phenomena are observed: (a) under some conditions the electrical mobility of Li+ is lower than that of the larger cation, (b) at a given temperature the mobility of Li+ decreases with increasing molar volume of the mixture, and (c) at low temperatures the isotherms of the mobility of the large cation show a maximum at some low concentration of that ion. These phenomena are interpreted in terms of the free space and the pair potential between cation and anion.