High-voltage conductivity of $\alpha$-Rb$_4$I$_5$, $\alpha$-KAg$_4$I$_5$, and $\alpha$-KCu$_4$I$_5$ superionic conductors

It is found that the conductivity of $\alpha$-Rb$_4$I$_5$, $\alpha$-KAg$_4$I$_5$, and $\alpha$-KCu$_4$I$_5$ solid electrolytes in the $\alpha$-phase rises with the electric field strength and tends to a limit value in fields on the order of 1 MV/m. The high-voltage limit of conductivity exceeds the low-voltage one by 100% or more. The application of an intense electric pulse raises the conductivity of the electrolytes by 35%, and the activated state exhibits an anomalously long relaxation time.