NMR and conductivity study of the protonic conductor HPb2Nb3O10·nH2O

Electrical conductivity and 1H Nuclear Magnetic Resonance (NMR) techniques were used to investigate the ion-exchanged layered lead-niobate perovskite HPb2Nb3O10·nH2O, over the temperature range 90–350 K. Compounds were synthesized by the sol–gel method and calcinated at 650°C. Analysis of the NMR data gives activation energies for the proton motion in the range 0.14–0.40 eV, which are dependent on the water content. The frequency and temperature dependencies of the proton spin–lattice relaxation times show that the character of the motion of the water molecules is essentially two-dimensional, reflecting the layered structure of the material. The 1H line-narrowing transition and the single spin–lattice relaxation rate maximum, observed in the hydrated compounds, are consistent with a Grotthuss-like mechanism for the proton diffusion.