Li Ion Dynamics in Nanocrystalline and Structurally Disordered Li₂TiO₃

Abstract

The monoclinic polymorph of Li 2 TiO 3 (β-form) is known to be a relatively poor Li ion conductor. Up to now, no information is available on how the ion transport properties change when going from well-ordered crystalline Li 2 TiO 3 to a structurally disordered form with the same chemical composition. Here, we used high-energy ball milling to prepare nanocrystalline, defect-rich Li 2 TiO 3 ; ion dynamics have been studied via impedance spectroscopy. It turned out that ball milling offers the possibility to enhance long-range ion transport in the oxide by approximately 3 orders of magnitude. Its effect on the oxide ceramic is two-fold: besides the introduction of a large number of defects, the originally μm-sized crystallites are decreased to crystallites with a mean diameter of less than 50 nm. This process is accompanied by a mechanically induced phase transformation towards the α-form of Li 2 TiO 3 ; besides that, a significant amount of amorphous materials is produced during milling. Structural disorder in nanocrystalline as well as amorphous Li 2 TiO 3 is anticipated to play the capital role in governing Li ion dynamics of the sample finally obtained.

Empirical Electronic Polarizabilities: Deviations from the Additivity Rule. II. Structures Exhibiting Ion Conductivity

“…Therefore, the VDP method cannot be applied. Although the ion conductivity has not been measured, the conductivity of the cubic α‐Li 2 TiO 3 phase is stated to be 3 orders of magnitude higher than the value 4 × 10 −6 ohm −1 cm −1 obtained on monoclinic β‐Li 2 TiO 3 = (Li 2.67 Ti 1.33 O 4 ) at 573 K . The other cubic phases Li 2.2 Mg 0.70 Ti 1.1 O 4 and Li 1.8 Mg 1.3 Ti 0.9 O 4 having the α‐Li 2 TiO 3 structure are also expected to have high ion conductivity.…”

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

“…The ball milling-induced phase transformation from β-to α-Li2TiO3 has already been mentioned by Brandstätter et al [16], but no further investigation in terms of a quantitative conversion was conducted. In Figure 7, PXRD measurements of β-Li2TiO3 before and after milling with (a) ZrO2 tools and (b) WC tools at different parameters are shown.…”

“…High energy ball milling of LiOH with rutile or anatase as titania precursors in yttrium stabilized zirconia (ZrO2) and tungsten carbide/cobalt hard metal (WC) tools leads to the formation of new reflections in the X-ray diffractogram which may be indexed by a cubic unit cell, as already noted in a previous study [19]. The new reflections could be assigned to either LiTiO2 or Li2TiO3 with NaCl type structure (SG Fm−3m) and a refined lattice parameter a varying between 4.15 and 4.16 Å , Ball milling of monoclinic β-Li 2 TiO 3 enhances the long-range ion transport, while also inducing a partial transformation to the cubic α polymorph and amorphization, but neither quantitative conversion nor details of the structural properties or phase compositions after milling have been reported yet [16]. The α polymorph may also be obtained by milling of NaOH, LiCl and TiO 2 , but subsequent washing to remove NaCl is necessary and no structural characterization of the product is given [17].…”

“…Li 2 TiO 3 represents an interesting system for high energy ball milling because of the three known polymorphs that might be converted under the milling conditions depending on the energy impact. The monoclinic low temperature modification β-Li 2 TiO 3 ( Figure 1a) with space group C2/c has a Ball milling of monoclinic β-Li2TiO3 enhances the long-range ion transport, while also inducing a partial transformation to the cubic α polymorph and amorphization, but neither quantitative conversion nor details of the structural properties or phase compositions after milling have been reported yet [16]. The α polymorph may also be obtained by milling of NaOH, LiCl and TiO2, but subsequent washing to remove NaCl is necessary and no structural characterization of the product is given [17].…”

Structure and ion dynamics of mechanosynthesized oxides and fluorides

“…macroscopic ion transport [5,7,8,[28][29][30][31]. In general, boundaries of grains or crystallites diverge in their behavior from bulk material.…”