Mechanochemical Induced Structure Transformations in Lithium Titanates: A Detailed PXRD and ⁶Li MAS NMR Study

Lithium titanates are used in various applications, such as anode materials for lithium intercalation (Li₄Ti₅O₁₂) or breeding materials in fusion reactors (Li₂TiO₃). Here, we report the formation of nano-crystalline lithium titanates by a mechanochemical approach and present a deeper insight into their structural characteristics by X-ray diffraction (XRD) and solid-state NMR spectroscopy. The compounds were synthesized in a high-energy planetary ball mill with varying milling parameters and different grinding tools. NaCl type Li₂TiO₃ (α-Li₂TiO₃) was formed by dry milling of lithium hydroxide with titania (rutile or anatase) and by a milling induced structure transformation of monoclinic β-Li₂TiO₃ or spinel type Li₄Ti₅O₁₂. Heating of mechanochemical prepared α-Li₂TiO₃ induces a phase transformation to the monoclinic phase similar to hydrothermal reaction products, but a higher thermal stability was observed for the mechanochemical formed product. Microstructure and crystallographic structure were characterized by XRD via Rietveld analysis. Detailed phase analysis shows the formation of the cubic phase from the various educts. A set of two lattice parameters for α-Li₂TiO₃ was refined, depending on the presence of OH⁻ during the milling process. An average crystallite size of less than 15 nm was observed for the mechanochemical generated products. The local Li environment detected by ⁶Li NMR revealed Li defects in the form of tetrahedral instead of octahedral site occupation. Subsequent adjustment of the structural model for Rietveld refinement leads to better fits, supporting this interpretation. View Full-Text