Proton dynamics in Rb3H(SO4)2 doped with Mn2+ studied by EPR and impedance spectroscopy

The temperature dependence of the linewidth ΔBpp and spin Hamiltonian parameters of Rb3H(SO4)2 (RHS) crystals were studied by X-band continuous-wave electron paramagnetic resonance. Direction cosines of the zero-field-splitting (ZFS) tensor and the coordination of the Mn2+ impurities in the crystal lattice were determined in the temperature range 20-450 K. The EPR spectra of crystalline samples and their irreversible changes into pseudo-powder spectra after heating above the superprotonic phase transition temperature were found. Our studies of electric conductivity have shown that, for crystals doped with Mn2+ ions, the conductivity values increase after heating by about one order of magnitude at intermediate temperatures (below the transition temperature to the superionic phase) in comparison with those of the pure RHS.