NMR and conductivity study of the protonic conductor HPb2Nb3O10 center dotnH(2)O

Electrical conductivity and H-1 Nuclear Magnetic Resonance (NMR) techniques were used to investigate the ion-exchanged layered lead-niobate perovskite HPb2Nb3O10. nH(2)O, over the temperature range 90-350 K. Compounds were sy nthesized by the sol-gel method and calcinated at 650 degreesC. 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 t emperature dependencies of the proton spin-lattice relaxation times show th at the character of the motion of the: water molecules is essentially two-d imensional, reflecting the layered structure of the material. The H-1 line- narrowing transition and the single spin-lattice relaxation rate maximum, o bserved in the hydrated compounds, are consistent with a Grotthuss-like mec hanism for the proton diffusion. (C) 2000 Elsevier Science B.V. All rights reserved.