Cation Distribution in Ordered Spinels of the Li2O–TiO2–Fe2O3System (original) (raw)

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

Physica Status Solidi (a), 2003

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.): (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 ( ⟷ 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.

Structural and electronic properties of the spinel Li4Ti5O12

Mongolian Journal of Chemistry

In this study, the structure and electronic properties of the spinel compound Li4Ti5O12 (LTO) are investigated both theoretical and experimental methods. The experimental studies of structural and electronic properties were performed by X-ray diffraction and UV-visible spectroscopy. The first principles calculations allowed to establish the relationship between the structure and electronic properties. The spinel type structure of LTO is refined by the Rietveld analysis using the X-ray diffraction (XRD). The band gap of LTO was determined to be 3.55 eV using the UV-visible absorption spectra. The Density functional theory (DFT) augmented without and with the Hubbard U correction (GGA and GGA +U+J0) is used to elucidate the electronic structure of LTO. We have performed systematic studies of the first principles calculations based on the GGA and GGA+U for the crystal structure and electronic properties of spinel LTO. We propose that a Hubbard U correction improves the DFT results.