Protonic inter-H-bond motion and ionic conductivity in hydrogen-bonded proton glasses

Low-frequency dynamics of the hydrogen-bonded proton glass Rb1-x(NH4)(x)H2A sO4 and its deuterated form has been investigated by measuring the decay of the NMR transverse nuclear-spin magnetization of Rb-87 nuclei in a spatial ly inhomogeneous electric-field gradient, H-1 line shape and H-2 two-dimens ional exchange NMR techniques. A large difference in the time scales of the decay of Hahn echo and Carr-Purcell echo train was observed between room t emperature and 10 K. The Hahn echo decay curves showed an exponential decay with the exponent proportional to the cube of time that is characteristic for random stochastic atomic motions. The proton NMR spectrum demonstrates the presence of mobile protons which produce a motionally narrowed absorpti on line above 220 K. Two-dimensional exchange NMR experiment on the deutera ted glass demonstrated the existence of slow thermally activated deuteron h opping between different hydrogen bonds, the process that represents the io nic conductivity. The same effects were observed also in several pure compo unds of the KH2PO4 family. The observed low-frequency dynamics is not a pec uliarity of the proton glass phase but represents the protonic inter-H-bond motion and ionic conductivity that is a common feature of the KH2PO4 famil y. [S0163-1829(99)02705-8].