Epitaxial Fe3−xTixO4films from magnetite to ulvöspi

Abstract

Epitaxial films along the Fe 3-x Ti x O 4 (titanomagnetite) compositional series from pure endmembers magnetite (Fe 3 O 4 ) to ulvöspinel (Fe 2 TiO 4 ) were successfully grown by pulsed laser deposition on MgO(001) substrates. Characterization including high resolution x-ray diffraction, x-ray photoelectron spectroscopy, and synchrotron-based x-ray absorption and magnetic circular dichroism consistently shows that Ti(IV) substitutes for Fe(III) in the inverse spinel lattice with a proportional increase in lattice Fe(II) concentration. No evidence of Ti interstitials, spinodal decomposition, or secondary phases was found in the bulk of the grown films. At the uppermost few nanometers of the Ti-bearing film surfaces, evidence suggests that Fe(II) is susceptible to facile oxidation, and that an associated lower Fe/Ti ratio in this region is consistent with surface compositional alteration to a titanomaghemite-like composition and structure. The surface of these films nonetheless appear to remain highly ordered and commensurate with the underlying structure despite facile oxidation, a surface condition that is found to be reversible to some extent by heating in low oxygen environments.

Phase Dynamics on Conversion-Reaction-Based Tin-Doped Ferrite Anode for Next-Generation Lithium Batteries

“…The Fe K-edge XANES spectra of all the Fe 3−x Sn x O 4 /rGO composites lie between those of FeO and γand α-Fe 2 O 3 , as shown in Figure 1c, which indicates that the oxidation state of iron ranges between Fe 2+ and Fe 3+ , consistent with the above XPS results (Figure S4b, SI). 25,34,35 For comparison, the XANES spectra of bulk iron oxides, commercially available FeO, Fe 3 O 4 , γ-Fe 2 O 3 , and α-Fe 2 O 3 , are also displayed as a reference. The oxidation state of iron starts from being close to that of bulk Fe 3 O 4 and, more importantly, decreases with the increment in tin content.…”

Infrared optical absorption in low-spin Fe2+-doped SrTiO3

“…Similar behavior has been previously observed in Fe 2 TiO 4 spinels, with Fe 3+ present at the surface and Fe 2+ in the bulk. [18] On the other hand, given the instability of the FeO phase and its propensity to incorporate some Fe 3+ ions in the bulk, [17] it is also possible that Fe 3+ is present in the bulk of the film. For both samples, the Ti 2p spectra (Figure 1(b)) clearly reveal Ti 4+ , albeit with a slight peak broadening.…”

Ion irradiation of Fe-Fe oxide core-shell nanocluster films: Effect of interface on stability of magnetic properties

“…MgO (100) (9.35 mm diameter circular or 10 mm square) substrates were used to deposit epitaxial films of Fe 3 O 4 by pulsed laser deposition (PLD). 38 To minimize the deposition of molten droplets and particles during the laser ablation process, an off-axis growth configuration was utilized. All growths were performed in 10 mTorr of N 2 .…”