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

Abstract

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.