The low-frequency dynamics of the H-bonded proton glass, and its deuterated form, were investigated by using the decay of the nuclear magnetic resonance transverse nuclear-spin magnetization of 87Rb nuclei in a spatially inhomogeneous electric-field gradient, the 1H line-shape and 2H 2-dimensional exchange nuclear magnetic resonance techniques. A large difference in the time-scales of the decay of the Hahn echo and Carr-Purcell echo train was observed between room temperature and 10K. The Hahn echo decay curves exhibited an exponential decay, with the exponent being proportional to the cube of the time. This was characteristic of random atomic motion. The proton nuclear magnetic resonance spectrum indicated the presence of mobile protons which produced a motionally narrowed absorption line above 220K. Two-dimensional exchange nuclear magnetic resonance data for the deuterated glass indicated the existence of slow thermally activated deuteron hopping between different H bonds; a process which constituted ionic conductivity. The same effects were also observed in several pure compounds of the KH2PO4 family. The observed low-frequency dynamics were not peculiar to the proton glass phase, but represented a protonic inter H-bond motion and ionic conductivity that was a common feature of the KH2PO4 family.
Protonic Inter H-Bond Motion and Ionic Conductivity in Hydrogen-Bonded Proton Glasses. M.Karayanni, G.Papavassiliou, M.Fardis, F.Milia, J.Dolinšek: Physical Review B, 1999, 59, 3534-9