NMR study of fast protonic conduction in layered HLa₂NbTi₂O₁₀·1.5H₂O

Abstract

Protonic motion in the layered compound HLa₂NbTi₂O₁₀ · 1.5H₂O has been studied by various NMR experiments. The ¹H NMR relaxation times T₁, T_1ρ and T₂ have been measured as functions of temperature. At 110 K, the rigid-lattice spectrum is observed which consists of a strong central signal flanked on either side by broader wings. From the line shape analysis of the spectrum it is concluded that the protons of the water molecules and the cage protons exist distinctly and do not form H₃O⁺ ions. The signals show motional narrowing beginning at ~ 190 K indicating the onset of protonic diffusion. The relaxation data have been analysed taking into account the layered structure of the material. Magic angle spinning shows a single signal at 4.47 ppm with respect to TMS. The mechanism of protonic motion in HLa₂NbTi₂O₁₀·1.5H₂O is discussed in the light of these NMR results.