From Micro- to Nanostructured Fast Ionic Conductor Li_0.30La_0.56◻_0.13TiO₃: Size Effects on NMR Properties

Abstract

This paper is devoted to the study of the changes in the NMR properties in the ionic superconductor Li0.3La0.56◻0.13TiO3 due to confinement. Stuctural studies were performed on micro- and nanostructured materials with grain sizes from 1.2 μm to 14 nm using complementary techniques such as Powder X-ray Diffraction (PXRD) analysis, the Brunauer–Emett–Teller method (BET), Transmission Electronic Microscopy (TEM), and Scanning Electron Microscopy (SEM) techniques. Thermogravimetric Analysis (TGA) linked to mass spectroscopy (TGA-MS) was used to evidence surface reactivity and quantify the mass loss, and Fourier transform Infrared (FT-IR) measurements revealed the presence of carbonate. When the size decreases toward the nanometric scale, the strong surface reactivity leads to an Li+/H+ exchange which was observed on the 1H NMR spectrum. This spectrum is similar to the one of the exchanged compound (named HLTO) with an additional contribution due to the protons attached on the surface. These surrounding modifications and the confinement bring new boundary conditions leading also to the modification of the 7Li static and dynamical properties. Below 1 mm an additional line appears in the nanometric systems, and the Zeeman relaxation measured by T1 becomes more complex. Cross relaxation effects are highlighted in the saturation recovery magnetization of the proton and the lithium.