Proton mobility in liquid and frozen HClO₄·5.5H₂O: NMR and conductivity measurements

²H NMR spectra and conductivity of liquid and frozen HClO₄·5.5H₂O have been obtained over the temperature range of 140-300 K. The ²H NMR spectra show a gradual broadening of an isotropic resonance at lower temperature from Δν_1/2 = 2 Hz at ∼300 K to ∼50 kHz at 170 K. At even lower temperatures, flat-top spectra of breadth ∼170 kHz were observed. The presence of isotropic spectra above 170 K indicates that the deuterons (protons) are relatively mobile even in the frozen state. A plot of ln (1/Δν_1/2) vs (1/T), the Arrhenius plot, further reveals the presence of two phase transitions centered at 228 ± 2 and 180 ± 5 K. Conductivity measurements agree well with the NMR results. The activation energies were determined from NMR (conductivity) measurements to be 0.27 eV (0.29 eV) from 228 to 180 K and 0.40 eV (0.36 eV) from 180 to 140 K.