Cation ordering and order–disorder phase transitionin Co-substituted Li4Ti5O12 spinels

Abstract

In this paper we present the results of the synthesis, crystal structure investigations and in situ X-ray diffraction studies of the order−disorder phase transition in cobalt substituted lithium titanate oxide spinels, Li1.33xCo2−2xTi1+0.67xO4 (0 ≤ x ≤ 1). Depending on the chemical composition the samples crystallize in two space groups (S.G.): Fd3m (0 ≤ x ≤ 0.40 and x = 1) and P4332 (0.50 ≤ x ≤ 0.875). Samples crystallizing in the S.G. P4332 are ordered spinels with a cation ordering of the 1 : 3 type at octahedral 4b and 12d sites. The cation ordering in octahedral sites is full in the sample with x = 0.75 (Li and Ti occupy 4b and 12d sites, respectively) and decreases for samples with higher/smaller x. Changes of the extinction conditions and nonlinearities in the concentration dependence of the lattice parameter in the regions 0.40 < x < 0.50 and 0.875 < x < 1 indicate changes of the crystal symmetry (Fd3m ↔ P4332). The partially ordered spinel x = 0.50 has a convergent, reversible, order−disorder phase transition at TC = (1083 ± 10) K. Samples with x = 0.875 and 0.75 have an order−disorder phase transition out of our experimental ranges with TC(x = 0.875) < 973 K and TC(x = 0.75) > 1173 K. The mechanism of the phase transition is based on cation migration.

Spin glass formation in Li-substituted Co2TiO4spinel

“…The structure properties of Li 1.33x Co 2−2x Ti 1+0.67x O 4 samples were studied in detail and results have been reported in [8]. We shall here briefly summarize the crystal structure peculiarities which are essential for the consideration of magnetic properties.…”

“…The results on cation distribution and cation ordering, obtained according to the refined occupation number values [8], are given in table 1. It can be seen that magnetic Co 2+ ions in disordered spinel samples (x = 0.25, 0.40) are randomly distributed between two cation sites, 8a and 16d.…”

Crystal and Magnetic Structure of the System Li0.5+0.5xFe2.5−1.5xTixO4 (x=0.16, 0.44, and 0.72)

“…Similar results were found for other solid solutions with spinel structure. [15] Magnetic behaviour: Magnetic susceptibility measurements were carried out on the title samples. The results obtained for quenched and slowly cooled specimens were similar in both cases and the following discussion is devoted to the Q samples.…”

Synthesis and structural properties of lithium titanium oxide powder as-synthesized by two step calcination process

“…In the early 1990s, Dhan, Thackeray, and Ohzuku et al electrochemically characterized these oxides [4][5][6][7]. The end members of the series, that is LiTi 2 O 4 , showed metallic behavior with a dark blue color (superconducting below 11 K), and Li 4 Ti 5 O 12 showed a semiconducting behavior with a white color [2]. Despite this difference, both of these materials exhibit similar Li-insertion electrochemistry.…”

“…Li-Ti-O based materials or series are very attractive as anode candidate material because of high chemical stability at high temperature and the high reversibility of the lithium insertion reaction. This enables the development of batteries with a prolonged life cycle [2], although they have high Li-insertion voltage as shown in the series below compared with Si and Sn.…”