Influence of Mn2+ doping level on conductivity of (NH4)3H(SO4)2 superprotonic conductor

AC conductivity at frequencies 20 Hz–30 MHz on pure and Mn2+ doped (NH4)3H(SO4)2 single crystals and powdered samples was measured. A significant influence of Mn2+ dopant on the conductivity value especially below the temperature of fast-proton phase transition has been found. EPR measurements allow one to find the optimal doping level (4500 ppm) for the best conductivity properties. Molecular mechanism for conductivity enhancement is suggested and discussed.