Effet of high polarizability on mobilities in ionic melts

The effect of cations having high polarizability on the mobilities of coexisting cations as well as of the cations themselves has been studied for Ag⁺, Tl⁺ and Cs⁺ ions. We have previously found that the internal mobilities, u, of alkali ions in molten salts such as nitrates are well expressed by an empirical equation:u = [A/(V_m-V₀)] sxp(-E/RT), where V_m- is the molar volume, and A, V₀ and E are parameters nearly independent of coexisting cations. In binary melts (M, Ag)NO₃, u_M except for M=Li⁺ becomes smaller than expressed by this equation; Ag⁺ ion has a tranquilization effect on u_M. On the contrary, in (M, Tl)NO₃, u_M becomes higher than according to the equation, which means that Tl⁺ has an agitation effect on u_M. It is found that Cs⁺, having a high polarizability, also has an appreciable agitation effect.