Layer-by-layer epitaxial growth of polar FeO(111) thin films on MgO(111)

We report on the structural properties of epitaxial FeO layers grown by molecular beam epitaxy on MgO(111). The successful stabilization of polar FeO films as thick as 16 monolayers (ML), obtained by deposition and subsequent oxidation of single Fe layers, is presented. FeO/MgO(111) thin films were chemically and structurally characterized using low-energy electron diffraction, Auger electron spectroscopy and conversion electron Mossbauer spectroscopy (CEMS). Detailed in situ CEMS measurements as a function of the film thickness demonstrated a size-effect-induced evolution of the hyperfine parameters, with the thickest film exhibiting the bulk-wustite hyperfine pattern. Ex situ CEMS investigation confirmed the magnetic ordering of the wustite thin film phase at liquid nitrogen temperature.Comment: 12 pages, 5 figure

latka.p65

Abstract. Intermetallic REAuSn (RE = rare earth elements) compounds were studied by means of X-ray diffraction (XRD), magnetic measurements and 119 Sn Mössbauer spectroscopy. It was shown that the majority of them exhibit complex antiferromagnetic ordering at low temperatures. The nature of hyperfine interactions has been discussed based on γ-ray absorption spectroscopy together with magnetic and structural data. Lanthanide contraction is reflected in the lattice parameters and isomer shifts. Strong experimental arguments support correlation between crystallographic type of structure and magnetic disordering in investigated compounds

Impact of Cerium Oxide on the State and Hydrogenation Activity of Ruthenium Species Incorporated on Mesocellular Foam Silica

Herein, the impact of cerium species loaded on mesoporous silica of MCF type on the state and catalytic activity of ruthenium species was studied. Up to 20 wt.% of cerium was incorporated on the silica surface, whereas the same 1 wt.% of Ru loading was applied. The samples prepared were examined by low temperature N2 adsorption/desorption, XRD, XRF, ICP-OES, XPS and H2 chemisorption. The catalytic activity of the materials obtained was investigated in the transformation of levulinic acid to γ-valerolactone. It was documented that the presence of Ce favored an increase in the dispersion of ruthenium species, which had a positive impact on the hydrogenation activity for up to 10 wt.% of Ce. Nevertheless, the highest cerium loading had a negative influence on the textural parameters of the support

Identification of iron species in FeSiBEA by DR UV–vis, XPS and Mössbauer spectroscopy : influence of Fe content

International audienceThe nature of iron in FeSiBEA zeolite was identified using DR UV-vis, XPS and Mössbauer spectroscopy. Various FexSiBEA zeolites (x = 3.8, 8.2 and 15 wt.%) were prepared by a two-step post synthesis method, which consisted in the creation of vacant T-atom sites by dealumination of tetraethylammonium BEA zeolite with nitric acid and then impregnation of resulting SiBEA with an aqueous solution of Fe(NO3)3. The incorporation of iron into the framework of SiBEA was evidenced by XRD. In Fe3.8SiBEA with low Fe content mainly framework tetrahedral Fe(III) species is present, in contrast, with high Fe content additional octahedral FeOx oligomers (Fe8.2SiBEA) and iron oxides (Fe15SiBEA) occur. The presence of iron in its 3+ oxidation state as isolated tetrahedral Fe(III) species for low metal content was demonstrated by DR UV-vis, XPS and Mössbauer spectroscopy. Moreover, the presence of Fe(III) species in two different tetrahedral environments was evidenced by Mössbauer results. For high iron content, diffuse reflectance UV-vis and Mössbauer spectra revealed additional presence of extra-framework FeOx oligomers. After calcination and rehydration significant amounts of oxide phases are formed, which were evidenced by DR UV-vis, Mössbauer spectroscopy and XPS