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The structures of Ruddlesden–Popper n = 2 member phases Sr3−xYxFe1.25Ni0.75O7−δ with 0 ≤ x ≤ 0.75 have been investigated using neutron powder diffraction and K-edge Fe and Ni EXAFS/XANES spectroscopy in order to gain information about the evolution of the oxygen vacancy distribution and Fe/Ni oxidation state with x. Both samples prepared at 1300 °C under a flow of N2(g), with δ = 1.41–1.00, and samples subsequently annealed in air at 900 °C, with δ = 0.44–0.59, were characterized. The as-prepared x = 0.75 phase has δ = 1, the O1 atom site is vacant, and the Fe3+/Ni2+ ions have a square pyramidal coordination. With decreasing x the O3 occupancy decreases nearly linearly to 81% for x = 0, while the O1 occupancy increases from 0 for x = 0.4 to 33% for x = 0. The air-annealed x = 0.75 sample has a δ value of 0.59 and the Fe3+/Fe4+/Ni2+/Ni3+ ions have both square pyramidal and octahedral coordination. With decreasing x, the δ value decreases to 0.45 for x = 0, implying an increase in the oxidation states of Fe/Ni ions. EXAFS/XANES data show that for the as-prepared samples the coordination changes are predominantly for Ni2+ ions and that the air-annealed samples contain both Fe3+/Fe4+ and Ni2+/Ni3+ ions.

After having emerged as primary contenders in the race for highly efficient optoelectronics materials, organolead halide perovskites (OHLP) are now being investigated in the nanoscale regime as promising building blocks with unique properties. For example, unlike their bulk counterpart, quantum dots of OHLP are brightly luminescent, owing to large exciton binding energies that cannot be rationalized solely on the basis of quantum confinement. Here, we establish the direct correlation between the structure and the electronic band-edge properties of CH3NH3PbBr3 nanoparticles. Complementary structural and spectroscopic measurements probing long-range and local order reveal that lattice strain influences the nature of the valence band and modifies the subtle stereochemical activity of the Pb2+ lone-pair. More generally, this work demonstrates that the stereochemical activity of the lone-pair at the metal site is a specific physicochemical parameter coupled to composition, size and strain, which can be employed to engineer novel functionalities in OHLP nanomaterials. 2016 the Owner Societies. The study was financially supported by the Knut and Alice Wallenberg Foundation and the Swedish Research Council. Collaboration within the NanoLund consortium is acknowledged. Q. Z. and K. Z. acknowledge support from by NPRP grant # NPRP7-227-1-034 from the Qatar National Research Fund (a member of Qatar Foundation). S. E. C. acknowledges funding from SFB 1073. The help from Dr Trudy Bolin at the 9-BM beamline of APS, USA is also greatfully acknowledged. Scopus

Molecular hydrogen exists in two spin-rotation coupled states: parahydrogen and orthohydrogen. Due to the variation of energy with rotational level, the occupation of ortho- and parahydrogen states is temperature dependent, with parahydrogen being the dominant species at low temperatures. The equilibrium at 20 K (99.8% parahydrogen) can be reached by natural conversion only after a lengthy process. With the use of a suitable catalyst, this process can be shortened significantly. Two types of commercial catalysts currently being used for ortho- to parahydrogen conversion are: iron(iii) oxide (Fe2O3, IONEX®), and chromium(ii) oxide doped silica catalyst (CrO·SiO2, OXISORB®). We investigate the interaction of ortho- and parahydrogen with the surfaces of these ortho-para conversion catalysts using neutron vibrational spectroscopy. The catalytic surfaces have been characterized using X-ray absorption fine structure (XAFS) and X-ray/neutron pair distribution function measurements.

Iron-mediated synthesis of alkali metal iodides was quite unexpectedly demonstrated to be able to serve as a cost-efficient and reliable source of spherical single crystalline near-stoichiometric magnetite (Fe3O4) nanoparticles as revealed by TEM and XRD studies and also by XANES spectroscopic quantification of the Fe2+-content. Using the particles as nuclei for the Stoeber synthesis of silica nanoparticles, core-shell magnetic material has been produced. The nature of the magnetic component was probed by XANES spectroscopy. The size of the particles is dependent on the synthesis conditions and Si : Fe ratio but can be kept below 100 nm. It is the Si : Fe ratio that determines the stability of the particles in acidic medium. The latter was investigated spectrophotometrically as leaching of Fe3+-cations. Considerable stability was observed at Si : Fe > 10, while at Si : Fe >= 20 no measurable leaching could be observed in over 10 days. Magnetic nanoparticles with improved stability in acidic medium provide an attractive basis for creation of adsorbent materials for applications in harsh media.