Reversible perovskite-fluorite phase transition in alumina-supported CeFeO_x films

Abstract

Thin films with a stoichiometry of CeFeOx were conformally deposited on high-surface-area γ-Al2O3 by Atomic Layer Deposition (ALD). X-ray diffraction (XRD) patterns, High-Resolution Transmission Electron Microscopy (HRTEM) images, Raman spectra,...

Effect of Perovskite-Fluorite Phase Transition on the Catalytic Activity of Pt/CeFeOx

“…TPO was also performed on the reduced Pt/CeFeO x /γ-Al 2 O 3 sample and is shown in Figure S3. A prominent O 2 consumption peak occurs at 765 °C which is consistent with what was observed in our previous study of the CeFeO x /γ-Al 2 O 3 support where temperatures in excess of 650 °C were required to completely oxidize the CeFeO x film.…”

“…Based on peak widths at half maximum, the crystallite size of the LaFeO 3 perovskite phase was 8.7 nm, which is much larger than the thickness of the film. As shown elsewhere, the perovskite crystals form two-dimensional crystallites of varying orientation, and the crystallite size determined from XRD analysis is representative of the in-plane dimensions. , The XRD patterns of oxidized and reduced CeFeO x /γ-Al 2 O 3 are shown in Figure c and have been discussed in detail elsewhere . The oxidized sample exhibits primarily fluorite peaks while the reduced sample primarily perovskite peaks.…”

“…When growing a CeFeO x film, a super cycle consisting of three Fe deposition cycles, followed by five Ce cycles, was used to grow a film with a Ce–Fe ratio of one. Sixteen super cycles were required to achieve a CeFeO 3 loading of 61 wt %, which corresponds to a nominal film thickness of 2 nm . To compare the properties of CeFeO x with LaFeO 3 , a LaFeO 3 /MgAl 2 O 4 sample was also examined.…”

“…The perovskite form, CeFeO 3 , is analogous to LaFeO 3 and can be prepared with difficulty as a bulk oxide. , Unfortunately, the bulk perovskite is unstable, as shown by the fact that, after high-temperature oxidation, high-temperature reduction does not bring back the perovskite structure. However, some of us have demonstrated that thin CeFeO x films, formed by atomic layer deposition (ALD) on an alumina support, can reversibly transition from a fluorite structure upon oxidation to a perovskite structure upon reduction . Spectroscopic data suggest that it is the Ce that changes the oxidation state, between +4 and +3 in these films, while Fe remains primarily in the +3-oxidation state.…”

Thermodynamic and Structural Properties of Bulk and Thin-Film CeVO4 and LaVO4

“…In another example, thin films of CeFeO following oxidation to a perovskite structure following reduction, even though the corresponding bulk material irreversibly separated into CeO 2 and Fe 2 O 3 phases following redox treatments. 14 In the present study, we set out to investigate CeVO x films on γ-Al 2 O 3 in order to understand the structure and redox thermodynamic properties of thin films with this composition. Because the properties of the oxidized CeVO 4 film were found to be very different from that of the bulk material, both in crystal structure and the oxidation states of the metal cations, we also examined the structure and equilibrium thermodynamics of LaVO x films in order to determine the effect of the rare-earth cations on these properties.…”