Extremely slow Li ion dynamics in monoclinic Li 2TiO 3 - Probing macroscopic jump diffusion via 7Li NMR stimulated echoes

Abstract

A thorough understanding of ion dynamics in solids, which is a vital topic in modern materials and energy research, requires the investigation of diffusion properties on a preferably large dynamic range by complementary techniques. Here, a polycrystalline sample of Li 2TiO 3 was used as a model substance to study Li motion by both 7Li spin-alignment echo (SAE) nuclear magnetic resonance (NMR) and ac-conductivity measurements. Although the two methods do probe Li dynamics in quite different ways, good agreement was found so that the Li diffusion parameters, such as jump rates and the activation energy, could be precisely determined over a dynamic range of approximately eleven decades. For example, Li solid-state diffusion coefficients D σ deduced from impedance spectroscopy range from 10 -23 m 2 s -1 to 10 -12 m 2 s -1 (240-835 K). These values are in perfect agreement with the coefficients D SAE deduced from SAE NMR spectroscopy. As an example, D SAE = 2 × 10 -17 m 2 s -1 at 433 K and the corresponding activation energy determined by NMR amounts to 0.77(2) eV (400-600 K). At room temperature D σ takes a value of 3 × 10 -21 m 2 s -1. This journal is © 2012 the Owner Societies