Maria Angeles Arillo

Crystal structure and electrical properties of LiFeTiO4 spinel

Abstract The complex oxide LiFeTiO 4 was prepared by an usual solid state method and its crystal structure has been refined by Rietvelds analysis of powder X-ray diffraction data. These results indicate a spinel-type structure in which all titanium cations are in octahedral sites whereas lithium and iron cations are distributed on tetrahedral and octahedral sites, nearly in the same ratio, that could be expressed by the formula: (Li 0.47 Fe 0.53 )[Li 0.53 Fe 0.47 Ti]O 4 . The ionic conductivity measured on polycrystalline samples has been obtained by ac techniques in the temperature range of 473–873 K.

Surface characterisation of spinels with Ti(IV) distributed in tetrahedral and octahedral sites

The differences of the binding energy of the Ti 2p 3/2 electron obtained by X-ray photoelectron spectroscopy (XPS) in ternary spinels such as LiFeTiO 4 , LiMnTiO 4 and LiCrTiO 4 have been studied. X-ray diffraction patterns for these spinels and neutron powder diffraction data for LiFeTiO 4 , LiMnTiO 4 and LiCrTiO 4 reveal that Fe(III) is in octahedral and tetrahedral sites, and Cr(III) and Mn(III) are exclusively in octahedral sites. However, Ti(IV) cations are distributed 100% in octahedral sites for LiFeTiO 4 , 66% in octahedral sites and 34% in tetrahedral sites for LiMnTiO 4 , and 88% in octahedral sites and 12% in tetrahedral sites for LiCrTiO 4 . XPS studies confirm the oxidation state of the cations Fe(III), Cr(III), Mn(III) and Ti(IV); and using high resolution XPS (5.85 eV pass energy) it is possible to decompose the Ti 2p 3/2 signal in two peaks at 458.0 eV (68%) and at 458.7 eV (32%) assigned to octahedral and tetrahedral Ti(IV), respectively for LiMnTiO 4 . In the case of LiCrTiO 4 , the Ti 2p 3/2 signal could be decomposed in two peaks at 458.4 eV (87%) and 459.3 eV (13%) with a similar assignation than that observed for LiMnTiO 4 . A single Ti 2p 3/2 peak at 458.1 eV and corresponding to octahedral Ti(IV) was observed for LiFeTiO 4 .

Structural and electrical characterization of new materials with perovskite structure

Abstract The series M 1 − 3 x La 1 + x (MgW)O 6 , where M = Na, K and x = 0.0, 0.11, and 0.22, was obtained by solid state reacti air at 723 and 1273 K. The formulae were inferred from different techniques and they were in good agreement with the structure determinations. The structures could be referred to a perovskite-type and show an ordered arrangement of MgO 6 and WO 6 octahedra in the B-sites and also Na and La cations are ordered in layers into the A-sites. The electrical behaviour of these phases show that the activation energies are relatively high and they could be related to the previous structural analysis.

Electrochemical behaviour of LiCr1−xAlxTiO4 (0≤x≤0.4)

Abstract The electrochemical behaviour in lithium cells of the spinel oxides Li 1+ y Cr 1− x Al x TiO 4 is reported. This behaviour is based on the structural features and the electrical conductivity of these phases. The mobile Li + cations are located on tetrahedral 8 a sites and the remaining cations (Cr, Al, Ti) on the octahedral 16 d ones, and the host materials successfully undergo reversible Li intercalation at 1.5 V, which is attributed to the pair Ti 4+ /Ti 3+ . The inclusion of Al 3+ in the spinel structure enhances the electrochemical stability of these materials upon cycling although the specific capacity is lowered.

Electrical properties of LiCr1-xAlxTiO4 (0≤x≤0.4)

Abstract The conductivity measurements on polycrystalline samples have been obtained by ac techniques and the ionic transference number has been calculated by charge/discharge d.c. technique. In the LiCr 1- x Al x TiO 4 (0≤ x ≤0.4) spinel systems, at low x , the solid solutions are predominantly electronic conductors but on increasing x , the level of electronic conductivity decreases giving rise to materials that are mixed conductors.