Superprotonics–crystals with rearranging hydrogen bonds

Interest in superprotonic crystals M$_m$H$_n$(XO$_4$)$_{(m+n)/2}$ (M = K, Rb, Cs, NH$_4$; X = S, Se, P, As) is associated with the solution of the fundamental problem of modern condensed state physics, i.e., with the determination of the effect of the hydrogen subsystem on physicochemical properties of materials, including phase transitions. From the viewpoint of practical applications, these crystals are promising materials for developing various electrochemical devices, including fuel cell, and are actively studied for the purpose of stabilizing superprotonic phases. Based on experimental data, conclusions are drawn about structural mechanisms of variations in physical properties of a number of crystals of this family.